Natural Stone Moisture Management

Natural Stone Moisture Management

Published By: Masonry Magazine Natural Stone Guide | Date: November 2017 | Author: John Koester

Download Article

Stone: The Original Building Material

Structures built of stone have stood the test of time, both structurally and aesthetically. Stone is strong, available just about anywhere, and has an undeniable visual appeal. The economics of recent centuries have shifted from building structures primarily with rocks to only using real stone on the facades of high dollar edifices, and a smaller number of experienced stone masons are keepers of the generational knowledge of building with stone.

What’s Different About Building With Stone Today?

Buildings constructed today with natural stone function differently from those of centuries past in many ways. Much like how unit masonry changed from mass construction to masonry veneers, stone based construction no longer relies on stone for structural strength. Anchored stone and adhered thin stone veneers have become the new normal, relying on a structural backup wall instead of the stone for strength. These changes along with significant changes to the backup wall assembly over the past 50 years have sometimes had unintended consequences.

We’ve understood for a long time that reducing air leakage and improving thermal resistance of the building enclosure were beneficial to occupant comfort and energy consumption – but we haven’t fully appreciated the value of that air and energy flow on managing moisture in the building materials. The rush to air seal, insulate, reduce vapor drive and incorporate materials with reduced moisture capacity has led to an epidemic of moisture related wall failures that costs the industry billions of dollars each year. The wall failure epidemic has bounced around to EIFS, stucco, siding, brick, adhered stone, etc. anywhere it rains. We need to digest the lessons from these historic and ongoing problems. The recurring theme in these failures is that we need to help walls dry out, and get the detailing right.

Full Stone Bottom Of Wall Full Stone Bottom of Wall Sure Cavity creates a consistent and predictable drainage & ventilation gap along the entire wall. Self spaced Stone Cavity Weep creates frequent weep tunnels to drain moisture.

Full Stone Window Full Stone Window Windows & penetrations are high risk zones for moisture problems. Belt & suspenders approach: divert incidental moisture away from the window opening, provide weeps and a drip plate above the window.

Science of Managing Moisture

Most wall failures are caused by a small amount of water that can’t dry out. Anchored and adhered stone veneers are reservoir claddings – in other words, they have the ability to hold a lot of moisture. Masons have long known that using rainscreen design with a simple air gap behind a veneer is an effective water control that protects the backup wall. With adhered masonry systems and even anchored stone veneers the industry has traded the air gap (a physics based solution) for a WRB (water resistive barrier - a chemistry based solution).

Take note: physics beats chemistry. Water resistive barriers are imperfect – they are perforated by fastener holes, subject to cracking, and can lose water repellency when exposed to surfactants in cementitious materials and wood. Without an air gap, capillary action allows water to move up the wall, against gravity. Without an air gap, water trapped between the veneer and the WRB will find its way to the weak points and wreak havoc.

A predictable and continuous rainscreen drainage plane over the water resistive barrier, with weeps at the base, drains liquid water.

Ventilating that air gap creates a small amount of airflow that allows the wall to dry out. As long as the air gap is at least 1/8” (to ensure a capillary break) gravity drains the wall to keep it dry. And by the way, gravity (physics) isn’t compromised by fastener holes, cracking, or loss of repellency. Gravity works all the time.

High quality manufactured rainscreen drainage planes can be used to create and maintain a rainscreen air gap behind any veneer, including anchored and adhered stone.

Cavities in Anchored Masonry

The classic rainscreen approach was to maintain a clear 1” air space behind the veneer. The problem is the “clear” part. In stone and unit masonry mortar squeezings clog the cavity and block weeps. Including a one-inch minimum thickness of cement grout between the backing and the stone veneer complicates the situation further as subsequent courses are laid. Using mesh to suspend mortar above the weeps just moves the mortar dam up the wall 10”, stifling airflow and obstructing drainage. The solution that ensures the air gap is continuous is a manufactured rainscreen drainage plane from the top of the wall to the weeps.

Good Details for Managing Moisture

Building Consultant Mark Parlee cautions that “A wonderful drainage mat turns out to be a complete waste of money if you leave out weeps at the base of the wall.” The details matter. Anyone looking at a wall section should be able to do the pen test for drainage to verify the moisture management plan.

Starting at the top of the wall assembly, use a pen to trace the rainscreen drainage gap down to the bottom of the wall. Any time the pen is lifted, or travels outside of the assembly (like at a window) the system needs to either weep out of the wall or deflect moisture away from the discontinuity.

Write Your Reputation in Stone

The realm of stone masonry presents an opportunity to improve your resume and develop a reputation for high-level craftsmanship. Protect your reputation and reduce your risk by ensuring that moisture management is a priority on each project you take.

Full Stone Vented At Soffit Full Stone Vented At Soffit Ventilation increases the drying power of the wall system with air flow. Ventilated wall systems have vents at the top and bottom of the wall.

Full Stone Veneer Run To Grade On Wood Full Stone Veneer Run To Grade The premium appearance with run to grade stone takes good detailing. Follow the stone line with flashing and create weep tunnels on top of flashing. Ensure weeps drain above grade.

Getting to the Bottom of Moisture Management

Getting to the Bottom of Moisture Managment

Published By: Construction Canada | Date: February 2015 | Author: John Koester

Download Article

Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

There are numerous factors/phenomena that create misunderstandings that result in improper or inadequate moisture management design for the exterior building envelope. Let’s take a look at two of them, gravity and temperature.

It’s the lowest point that’s the wettest. Why, because that’s where the water is! (see figure 1) That’s because of the influence of gravity. Now the low point of an exterior wall system of a building doesn’t necessarily have to be the top of the footing (see figure 2) or the top of the stem wall. (see figure 3)

A low point in an exterior building envelope is a location that stops or slows moisture in liquid form from proceeding in a gravity-induced downward direction.  Sometimes this is intentionally done with a designed flashing system and sometimes it is just the result of other components of the exterior building envelope system coming together to stop or seriously slow the downward path of liquid water.  (see figure 4 and figure 5)

It’s the highest point that’s the wettest.  Why, because that’s where the water is!  (see figure 6) That’s because of the influence of temperature.  Everyone, or at least I hope every construction professional, can understand why a low point of a construction detail would be the wettest, but why would a high point/the top of a wall system be the wettest?  The answer is found in the fact that H2O can be in three forms:  a solid (ice), a liquid (water) and a gas (water vapor).

The most obvious conclusion is that there is a leak, a source of liquid water coming down and in from a higher point, and in most cases, that is exactly what is happening.  But there may be a number of other scenarios that could explain water and water patterns at a high point of an exterior wall detail.

One of them is that H2O in vapor form will move upward with warm air to a higher point of a construction detail and come in contact with air or a surface that is cool enough to be a dew point and condense into water droplets and liquid water and wet a construction detail. (see figure 7)

Figure 7 Figure 8 Figure 9 Figure 10

This can happen on exterior surfaces of a construction detail or on the interior surfaces of a construction detail (inside a wall).  (see figure 8)  The other part of the answer has to do with why a high point of a wall would be cool enough to be a dew point when hot air rises and the top of the wall and ceilings should be warmer.  This phenomenon is usually the result of a thermo bridge from the cold exterior of an exterior building envelope to a warm interior of an exterior building envelope with enough intensity to overcome the ability of the interior ambient air temperature to warm the construction detail. (see figure 7 and  figure 8)

The ingredients required to allow this to happen are an opening to allow a sufficient amount of cool air to pass into or through the construction detail at this point or a material that can transfer this difference in temperature, “good conductors” such as steel, glass, solid concrete, or water (water transmits temperature 25 times better than open air). Wet construction materials are good conductors of temperature and poor insulators. The best insulations that are wet are very poor insulators. So when a wet pattern in a high point of a construction detail is contributing to condensation, there very well may be an associated water source or wet material that has promoted cold temperature transfer (a water source that causes a temperature transfer and a dew point and a condensation wetting pattern but is not actually leaking or absorbing into a construction detail to wet it). (See figure 7 and figure 8)

Another mechanism that transports moisture in liquid form into and through construction details is absorption.  The general rule/law of physics says moisture will usually move from a high concentration of water into and through materials to a lesser concentration of water (drier materials) in an attempt to equalize the concentration of water.  The distances that this moisture can travel into and through construction materials is truly surprising!  (see figure 9)

If certain conditions exist, continuous source of liquid moisture, absence of driving mechanism and construction materials that funnel and or encapsulate (two or more) vapor retarders in the same exterior building envelope; the travel distance can be great. (see figure 10)

These distances will be expanded proportionally with the volume of the liquid moisture source. A large volume of liquid water has greater weight (pull of gravity) propelling the liquid moisture into and through construction materials.

It should be apparent that designing an exterior building envelope moisture management system brings a number of factors into consideration.

  • The potential amounts of moisture to be managed
  • How often the construction detail is exposed to this amount of moisture
  • The duration of the exposure
  • The physical form of the moisture (liquid, solid, gas)

The first, and most important, moisture management design requirement for your building’s details is “Do not let them get wet!”   They get wet quickly but they dry out slowly.  The second moisture management requirement is “Get the moisture away from, off of and out of your construction detail as quickly as possible.”  It’s about “Time.” The amount of time moisture is in, on or near your construction detail is really what you are managing.

Drainage is “the movement of moisture from one point where it is not desired to a preferred location.”  In most cases this is from a high point in a construction detail or surface on a construction detail to a lower point out of, or off of that construction detail.  In the interior of a wall of an exterior building envelope, this is a code compliant requirement.  Section 1403.2, Weather Protection, of the 2012 IBC states, “Exterior walls shall provide the building with a weather-resistant exterior wall envelope.  The exterior wall envelope shall include flashing, as described in Section 1405.4.  The exterior wall envelope shall be designed and constructed in such a manner as to prevent the accumulation of water within the wall assembly by providing a water-resistive barrier behind the exterior veneer, as described in Section 1404.2, and a means for draining water that enters the assembly to the exterior.  Protection against condensation in the exterior wall assembly shall be provided in accordance with Section 1405.3.”

Figure 11

The moisture that may enter the exterior building envelope must be provided with a designed passageway to move it from a high point of entry to a lower point and allow it to exit the exterior building envelope to the exterior of the building.  The technology that allows liquid moisture to move downward in the interior of an exterior building envelope is a core, cavity or a rainscreen drainage plane material.  The technology that stops the downward movement of liquid moisture is a waterproof flashing material.  The technology that gives liquid moisture a reason to go in one direction or another is slope-to-drain/elevation variation – “high to low.”  The technology that creates the opening from the interior of the wall to the exterior of the veneer/rainscreen material (brick, stone, stucco, etc.) is the weep.  (See figure 11)

All of these four components are absolutely critical for an exterior building moisture management system to work.  Weeps do not work until the liquid moisture gets to them.  If the moisture that is attempting to move downward in a core, cavity or rainscreen is obstructed or slowed, it may just absorb into adjoining construction material and/or deeper into the exterior building envelope.  If and when the liquid moisture gets to a flashing/water stop, if there isn’t any slope-to-drain to the exterior of the exterior building envelope, it may just accumulate and absorb into the adjoining construction material or find its way deeper into the exterior building envelope through a void in imperfect flashing or out through veneer material through an undesigned pathway.  If the weep holes are not at the lowest point of the core, cavity or rainscreen drainage plane, liquid water may accumulate and find its way deeper into the exterior building envelope or through veneer materials through an undesigned pathway.

All of these consequences of an improperly designed moisture management system are potentially very serious and may result in exterior building envelope component failure or total system failure, up to and including structural failure.  An exterior building envelope moisture management system’s reliance on all components of the system to function in concert with each other cannot be stressed enough!

Figure 11

Figure 13 Figure 14

The last and lowest (but certainly not “lowliest”) components are in many cases the least understood and prioritized – these are the weeps and weep screeds. (See figure 12 and figure 13)

In the case of weeps, materials used, the number used and their location is completely without reason.  Materials that are often used are thought to wick water out of a core or cavity.  Here is some really good advice – Do not get into a wicking contest with masonry materials!  A weep of any kind, good or bad, every 48 inches is of little value.  A weep of any kind that is not at the lowest point of a core or cavity which is at the top surface of the flashing or water stop, is of little value.  A weep that creates a hole in a veneer from the interior of the core or cavity to the exterior of the veneer is just another hole in the veneer that may let liquid moisture into the wall as well as let it out of the wall if there is no slope-to-drain that keeps it out and drains it out of the wall.

Weep screeds have very similar moisture management responsibilities, but in many cases they do not function appropriately.  The notion that a shrinkage crack between the metal and cementitious material (scratch coat, brown coat and bedding and grouting mortar) is a dependable moisture management detail is ludicrous. (see figure 14)

But for many popular/commonly installed weep screeds, that’s exactly what the literature says.  An example taken from a manufacturer’s weep screed literature states, “The ‘V’ stop is punched with holes primarily intended as keying mechanisms.  These also offer minor moisture weeping capabilities.  As stucco cures it shrinks slightly away from the ‘V’ stop allowing moisture to flow down the building paper and exit down the sloped surface.”

A weep and weep screed must have compatible moisture moving capacity with the core, cavity or rainscreen drainage plane above.  If not, the slowing of moisture movement will cause an accumulative effect with all the negative consequences.

Figure 15

What makes a good weep?  There are specific criteria to follow when choosing weep technology.  Masonry Design and Detailing (Bell, 1987) defines weep holes as “Openings placed in mortar joints of facing material at the level of the flashing to permit the escape of moisture.”  The voids/tunnels and channels that a weep creates through the bed joint of mortar, scratch coat, adhering mortar, etc. must be at the lowest point of a core, cavity or rainscreen drainage plane – where the water is – and must be no further than 12 inches apart. (see figure 15)

There is no need to consider modular configuration of masonry units because the voids/tunnels and channels are in the bottom side of the bed joint of mortar and do not affect layout or coursing.

What makes a good weep screed?  There are specific criteria to follow when choosing weep technology.   According to, “A weep screed is a type of building material used along the base of an exterior stucco wall.  The screed serves as a vent so that the moisture can escape the stucco wall finish just above the foundation.”  It is a device used to terminate the bottom of a cementitious-based thin veneer rainscreen.  This device should allow liquid moisture that drains down the back side of a thin veneer rainscreen and on the surface of the weather resistant barrier in the rainscreen drainage plane to freely exit the thin veneer 1.5” to 2” below the bottom of the framed wall system and the top of the stem wall.

Figure 16

Section 2512.1.2, Weep Screeds, of the 2012 International Building Code states, “A minimum 0.019-inch (0.5 mm) (No. 26 galvanized sheet gage), corrosion-resistant weep screed or plastic weep screed, with a minimum vertical attachment flange of 3.5 inches (89 mm) shall be provided at or below the foundation plate line on exterior stud walls in accordance with ASTM C 926.  The weep screed shall be placed a minimum of 4 inches (102 mm) above the earth or 2 inches (51 mm) above paved areas and shall be of a type that will allow trapped water to drain to the exterior of the building.  The weather-resistant barrier shall lap the attachment flange.  The exterior lath shall cover and terminate on the attachment flange of the weep screed.”  (see figure 16)

Figure 17-18

It is critical that the drainage holes/weep holes be numerous and not more than 1 inch (or so) apart and located at the bottom of the weep screed and against the 3.5” back flange to allow for direct contact with the bottom of the rainscreen drainage plane.  (see figure 17, figure 17A, and figure 17B) This is critical for two reasons:  First, the liquid moisture that drains down the rainscreen drainage plane will have an immediate exit point.  Second, the cementitious materials used to create the thin veneer will not have access to block them.  (see figure 18, figure 18A, and figure–– 18B)


There is little doubt that moisture will enter the building envelope and that it needs to be drained.  This has become more and more the accepted practice, and in many cases, code mandated.  Unfortunately, the liquid moisture gets drained to the bottom of the wall with little thought given as to how it will get out.  This article has presented pragmatic solutions to getting the moisture out at the bottom.  It is up to the reader to make prudent choices in the materials and methods they choose to employ.

Knowing the Unknown – Insights on the Ostrich Syndrome

Knowing the Unknown - Insights on the Ostrich Syndrome

Published By: Masonry Magazine | Date: December 2014 | Authors: John H. Koester,  and Mark A. Johnson,  Illustrations: Adam Skoda, Senior Graphic Designer

Download Article 

Who would have ever thought that could happen? How could they have known that would happen? No one could have known that would happen. No one could have predicted that! These common phrases are often heard after something bad has taken place. They are meant to lessen someone’s sense of responsibility and/or feelings of guilt related to a negative event or action. They are nice, humane gestures, but in many of these cases there is someone responsible, and they could have and should have known.

In the construction industry, many premature failures are a result of shortcuts taken to circumvent good standard practices. The reasons or excuses for taking these shortcuts are that they save time, they save material and that means they save money! The term “value engineering” sounds professional, but in many cases it is short-term gain with long-term negative consequences. If it is truly the same quality and quantity for less money, that is value gained. If it is just less quantity and quality for less money, there is no value gained, there is actually value lost! When construction professionals and others involved with a building project make a decision to take shortcuts on materials, quality and labor, the construction details involved don’t last as long and often end in catastrophic failure. The phrase “Who could have known that would happen?” doesn’t alleviate the situation!

When it comes to value engineering moisture management components, details and systems, you had better know what you are doing. Sometimes there are very good reasons for choosing a less expensive system; sometimes the owner’s budget just can’t afford the better, more expensive system. If the system is of the type that can be upgraded in the future when funds are available to do so, or if its service life can be extended with a good maintenance plan that allows for a “pay-as-you-go” solution, then choosing the less expensive system makes sense/cents. However, if it is the type of moisture management system that is incorporated into the exterior building envelope and not accessible at a later date for an upgrade or for maintenance, then the decision making process needs to be different.

The irony is that it is just this type of moisture management system that gets downgraded during some of the value engineering efforts. Not being accessible can mean it is buried (covered up) in a wall or roof system, or it can mean it is just hard to get to or just out-of-sight like in a high roof system. In any case these are not the parts of an exterior building envelope to cheapen up or cut corners. When moisture management systems fail prematurely, there are very few building materials in close proximity to this type of failure that will do well. Water is the universal solvent; given time all things succumb to water. And while it is happening, they look bad and in some cases, smell bad. They can also be hazardous to health and safety.

When Will Moisture Failures Show?

Mushrooms Growing on Stone WallAnother factor that needs to be considered when choosing a moisture management system is: “If it was to fail or if it was in the process of failing, when will it show? The real problem with some moisture management systems is that they can be in a failure mode for a long time, sometimes even for years, before the failure becomes outwardly apparent. In many cases the complete structure is in failure mode by the time it shows up as a cosmetic surface blemish. This has been the case with some major failures of the two coat stucco systems. The building owners started to notice discoloration on interior sheetrock or plaster or discoloration on exterior veneers. When the walls were opened up, the damage was so extensive the building could not be saved so they were condemned and demolished. The news reports have focused on stucco systems, but these types of catastrophic failure can, and do, occur in other veneer systems such as thin and full stone, thin and full brick and many other siding systems.

A real life example of this occurred in a home on Lake Michigan. A homeowner was doing some yard work around his 4 ½ year-old, 4 million dollar, full stone veneer house when he happened to notice a toad stool mushroom protruding from the surface of the stone around the chimney. When the wall was opened, the exterior building envelope forensic experts concluded the home was beyond repair! Unfortunately, this scenario is all too common. The surface blemish, either on the interior or exterior, that initially looks like a very minor problem is, in reality, a moisture management failure that has been in progress for a long period of time. And what at first looked like a cosmetic surface issue, is really an extensive and expensive structural failure problem. A very expensive home, with a high-quality full stone veneer, is jeopardized by a low cost or non-existent exterior building envelope moisture management system. Gee, who would ever have seen that coming?

Rot below housewrap behind thin stone veneer

Compatability & Systems Thinking

The terms material compatibility and holistic building are not just hot button topics. The selection of compatible building materials is critically important in sustainable building. The structural failure in the building envelope of the $4 million dollar Lake Michigan home was the result of incompatible building materials and a lack of holistic design and planning. A full stone veneer rainscreen is not a barrier system; therefore, the moisture that egressed through the full stone veneer was trapped behind the stone veneer and at the face of the weather resistant barrier (WRB). The moisture was trapped there for extended periods of time, allowing some of it to be absorbed into and through the WRB. Some of this moisture continued moving inward into and through the sheathing, reaching as far as the rim joists and rim joist plates. This trapped moisture spread like a cancer through the building envelope resulting in such devastation that the demolition contractor was able to scoop out ruined sheathing, studs and rim joists with his bare hands!

As bad as this sounds, it is not an uncommon entrapped moisture scenario. The IBC, Section 1403.2 “Weather Protection” states that there must be a method to drain water from the wall assembly. The IRC, Section 703.1.1 “Water Resistance” states that the wall assembly (building envelope) must include a method to drain any accumulated water. In other words if the rainscreen of the exterior building envelope is not a barrier system, the design of the exterior building envelope must provide a passageway for moisture that enters the system to efficiently drain back out of the system. An effective drainage plane system with a good weep system is needed. (B)Figure B

It is an unfortunate reality that the construction industry seems to need to be sued into compliance. The masonry industry receives many calls each year from legal firms inquiring about the availability of rainscreen drainage plane technology to the construction industry. The logical conclusion that can be reached from these inquiries is that someone is about to be sued for failing to include a rainscreen drainage system in the exterior building envelope resulting in structural failure from entrapped moisture. Construction professionals can, under limited circumstance, plead ignorance, but at a certain point, they will be held accountable.

Over the last 30-40 years the construction industry has experienced increased entrapped moisture problems in the exterior building envelope. These recurring moisture management problems have increased for a number of reasons: a less-skilled labor force, many new materials that often went unchecked for compatibility with other materials, deviations from standard construction practices (and in some cases, from code), and the lack of coordination between all parties involved in the construction project. The good news is that there are now ways to solve these issues both for financial gain and for the betterment of the construction industry, and a well-designed rainscreen drainage system is at the top of that list.

Figure CRainscreen drainage planes that are properly designed and installed in conjunction with the appropriate weep system and other required detail components, greatly diminish the risk of entrapped moisture in the exterior building envelope. (C) The rainscreen veneer of an exterior building envelope is the most exterior surface of a building envelope. It is the first surface that attempts to change the exterior ambient conditions to the desired interior ambient conditions. In many cases they are not barrier systems and are not designed to be barrier systems (see IBC, Section 1403.2 “Weather Protection” and IRC, Section 703.1.1 “Water Resistance”), and they do take on moisture. In most scenarios they do a number of things:

  • They protect other exterior building envelope components from UV damage.
  • They absorb and resist the kinetic energy of wind and wind-driven materials (snow, rain, hail, etc.).
  • They provide aesthetic appeal.
  • They facilitate maintenance.
  • They enhance durability (however, in most cases they are not structural).

Figures D-HCommon rainscreen veneers include stone, brick, stucco, man-made thin-stone, man-made thin-brick, thin stone, cladding and more. The layer immediately behind these rainscreen veneer materials should be a void or plane that separates the backside of the rainscreen from the other exterior building envelope components. In rainscreen walls with full brick or full stone veneers, this void/plane is commonly called a cavity. These cavities vary in width from a code compliant 1” to larger cavities of 2” to 4”. Some designs include rigid insulation installed in part of the cavity. For example the cavity will start off as a 4” void and then 2” of rigid insulation is installed in the cavity leaving a 2” air space. The 2” air space in this example (D) is the cavity.

For years stucco and other thin veneers (thin stone, thin brick, etc.) relied heavily on the use of lath to create a separation/void. In many cases this system consisted of 1” x 2” strips of wood nailed vertically onto the exterior sheathing and over the weather-resistant barrier (WRB); they were aligned with the studs. (E) This was an expensive solution because it was so labor-intensive. Its functionality was also closely tied to the labor force installing it.

The other most common rainscreen drainage detail involved two layers of weather resistant barrier material (WRB). Originally, this detail consisted of 1” x 12” wood boards laid horizontally over wood studs with little or no insulation. Two layers of asphalt-impregnated construction paper were placed on top of the wood backup wall. Next, expanded metal lath was fastened on top of the two layers of construction paper. The final layer consisted of three-coat stucco. (F) The theory behind the two layers of construction paper was that when moisture penetrated the stucco veneer and migrated into the construction paper, the top layer would wrinkle creating a drainage space or void for the moisture to travel downward and out of the building envelope. The drainage/drying capabilities of this configuration were generally satisfactory.

As time progressed the sheathing changed to 4’ x 8’ sheets of plywood and eventually to 4’ x 8’ sheets of OSB. The WRBs changed to various types of synthetics, and the studs changed to a 2” x 6” with a great deal of insulation. (G) Even the stucco changed with one or two coats becoming the norm; less material means less protection from moisture intrusion into the building envelope. The drainage/drying capabilities of this new configuration were generally less than satisfactory.

The rush to increase profits (or in some cases, just to maintain profits and stay competitive) had short-term gains, but long-term liabilities. There were lots of lawsuits because these systems failed. The products and systems also incurred a negative image in the construction industry. Customers suffered and so did the building industry.

In Canada these failures led to new codes that established requirements for rainscreen drainage planes (2005 National Building Code of Canada, Subsection, Minimum Protection from Precipitation Ingress. (H) In April 2010, Oregon began enforcing a code required rainscreen drainage plane (or gap) of at least 1/8”. (Oregon Residential Specialty Code 2008 sections R703.1 and R703.2) Many other states have pledged to enact building codes requiring rainscreen drainage and some U.S. municipalities have interpreted existing code to mean that building envelopes that don’t contain a barrier system must include rainscreen drainage.

Many large U.S. homebuilders and apartment builders have also begun to include rainscreen drainage in their projects. Unfortunately, this movement has been spurred on by extensive warranty claims and insurance losses. They are beginning to realize that the risk of entrapped moisture leading to structural failure far outweighs the cost of prevention secured by including a well-designed and installed rainscreen moisture management system (rainscreen drainage plane/mat, weeps and appropriate accessories).


There is a wealth of evidence pointing to the necessity of rainscreen building envelope moisture management systems. Records of structural failure and the resulting lawsuits and awards are easily found, and the number of countries, states and municipalities demanding their inclusion continues to grow. Any professional in the construction industry who continues to ignore their importance does so at his or her own peril. Do not be that character gazing at a moisture-related structural failure muttering those hollow words, “Who could have seen that coming?” You can’t afford it and neither can the construction industry. Be proactive and include a well designed, ICC and CCMC-R evaluated rainscreen drainage plane (with the appropriate weep system and accessories) in your next project, and say “Goodbye!” to the Ostrich Syndrome forever!

Living At The Edge

Living at the Edge

Published By: Construction Canada | Date: September 2014 | Author: John Koester

Download Article

The construction industry has witnessed an ongoing trend towards large dimension material panels over the last 60 to 70 years. 4’ x 8’ sheets of OSB and plywood have replaced 1” x 10” or 1” x 12” shiplap board stock as the sheathing material of choice for the exterior building envelope. The factors driving this trend include labor savings, better utilization of materials and the positive structural characteristics of these larger panels. Sheet stock construction material sizing has also increased, and for the same reasons. The use of 9’ to 10’ wide rolls of synthetic WRB in place of 40” to 54” rolls of asphalt impregnated roll stock is increasingly common.

All the components of the exterior building envelope are connected and have an impact on one another. While this impact may be slight, it’s still a factor. In the case of material panels, the expansion-contraction characteristics of a 4’ x 8’ sheet of plywood or OSB need to be considered and the appropriate detail needs to be designed. The reason this new detail design is required is “not” because plywood or OSB expands or contracts that much more or that much less than shiplap board stock; it’s because the expansion-contraction of the 4’ x 8’ sheet panels (32 sq. ft. area) is directed and occurs at the edges (joints) of the 4’ x 8’ panels. (see detail 1)

The same area of wall, roof or floor decking covered with the shiplap board stock may expand or contract a similar amount, but this expansion and contraction will not all accumulate and occur at the outside edge of the 32 sq. ft. area. Instead, it will be dispersed within this area between each 1” x 10” or 1” x 12” shiplap board stock. (see detail 2) This dispersion minimizes the movement, and therefore, minimizes the stress at the joints. (see detail 2)

This movement, and the stress it creates, impacts the other components of the exterior building envelope including the fastening mechanisms, structural members, covering membranes, coatings, etc.

There is another phenomenon that happens at the perimeter of the construction material panels; they curl up or down. When these panels of material experience a variance in moisture content and temperature (wet/dry, warm/cool) they expand and contract. This expansion and contraction creates stress patterns in the field of the panels. When the stress occurs in the center of the panels, there is adjoining material with similar stress patterns that oppose and neutralize the stress in the center. However, the perimeter doesn’t have this oppositional stress on all sides, and this allows the edges to distort and curl up or down. (see detail 3)

The edges of these construction material panels are also exposed to a third phenomenon, moisture penetration. Even if there isn’t any additional moisture at the perimeter of the panels, there is more surface for moisture to penetrate. (see detail 4) The surfaces of these edges may be more open to moisture because of saw cuts, exposure during shipping and poor storage methods at the job site. (see detail 5)

We stated earlier that all things in the building envelope are connected. So what’s the cumulative effect of moisture penetration and the expansion/contraction phenomena and the stress they create on the other components of the building envelope? The primary area of concern is the fastening mechanism (i.e. adhesives, welds or mechanical fasteners). If everything is known and the appropriate design details are correctly engineered and executed, the fastening details will withstand the stress put on them. If the fastening details are incorrectly designed or poorly executed, they will be overwhelmed by these stressors and the holistic synergy of the building envelope will be compromised. Additionally, the fastening mechanisms can fail at these general locations: Zone 1, Zone 2 and Zone 3. (see details 6 and 7)

Fastening mechanisms are required to hold materials in place. They are also required to do so following a certain “fastening pattern,” and that fastening pattern needs to be correctly engineered. (see detail 8)

Most fastening mechanism failures follow a “zipper-like” pattern. Stress is incorrectly compensated for and one or more fastening mechanisms stress to failure causing the released stress to transfer to the adjoining fastening mechanisms that in turn are overstressed to failure. This ultimately leads to overall system failure.

Fasteners are also affected by poor or improper installation techniques. Improper installation issues include adhesives that are installed on contaminated surfaces and do not bond (see detail 9) and mechanical fasteners that are carelessly installed causing them to miss the structural members, leaving them with little, if any, holding ability. These mechanical fasteners (screws, nails, staples, etc.) if not seated into structural members, tend to float and back out. This can cause point-pressure stress that may damage other components of the exterior building envelope such as moisture resistant materials and/or waterproof coatings. (see detail 10)

They also create unnecessary penetrations through the WRBs and act as thermo conductors through the sheeting and into stud, rafter and joist cavities. If these exposed fastener shafts or heads convey a dew point temperature, they may accumulate condensed moisture in the form of water droplets or frost. (see detail 11)

Large panels of construction materials also impact the exterior building envelope by directing air pressure equalization requirements to their perimeters. (see detail 13) This is generally true with all materials of any dimension, small or large, (see detail 14)but similar to the expansion-contraction movement of larger panels of material, it is directed and accumulates at the edges. (see detail 13) As with the expansion-contraction movement, there aren’t necessarily more or fewer pressure equalization requirements, it’s that they all occur at the perimeters of the larger area. This concentration in a smaller, more restricted area causes a unique phenomenon.

The negative results of a contaminant (in this case moisture) are directly connected to its physical form and its amount of concentration in a material or location. An example would be a gallon of water in vapor form dispersed throughout a house as opposed to a gallon of water in liquid form concentrated in a single window sill detail.

This phenomenon starts to occur immediately upon placement of a large dimension construction panel. The surfaces that are covered by these panels will have some degree of moisture concentration. Upon placement, a large construction panel begins restricting free air movement over a large area, and impacts the pressure of that volume of area. If the encompassed area holds high pressure, the high pressure will attempt to equalize with a lower pressure. If this lower pressure is located outside the perimeter of this construction panel, air from the high pressure area will move to the low pressure area and will take some moisture with it. (see detail 13 and 14)

This pressurized air, moving to a lower pressure and carrying moisture with it, is funneled through the perimeter edge joints of the large construction panels.(see detail 15)

When certain conditions prevail, such as dew points caused by the temperature of the ambient air or temperatures on the surfaces of material that the moisture-laden air moves past, water vapor may condense on and accumulate in the panel joints and on the surface adjacent to these joints. (see detail 16)

This liquid water will wet the surfaces in these joints and will absorb into their edges and into materials adjacent to the edges of the construction panels. This wetted material will, in turn, conduct temperature more readily than dry material thereby amplifying the negative condition. The failure of tape at the taped joints of large construction material panels may be attributed to this phenomenon. The joints are contaminated with moisture (a very good bond-breaker) before the tape is applied, and the tape’s ability to bond is degraded from the inside out. (see details 17 and 18) This condition is exacerbated when the taped seams (joints) fail and moisture is allowed into and behind the large construction panels from the outside in.

Smaller dimension sheeting and decking materials of the past (1” x 10” and 1” x 12” shiplap boardstock) had more seams (joints) to help disperse both expansion-contraction stresses and air pressure equalization requirements. (see detail 19)

Today’s larger construction panels need assistive technology to help them achieve maximal performance. This technology comes from drainage planes and rainscreen drainage planes, technology that has a twofold benefit. (see details 20 and 21) First, the void (or separation) that this technology creates between the layers of the exterior building envelope (exterior sheathing, outbound rigid boardstock insulation and exterior veneers) has, to a small degree, had a positive impact on expansion-contraction characteristics by allowing the movement to be smoother and more evenly dispersed. (They act as slip-sheets.)

The more important impact is that they are designed pathways for moisture that may attempt to accumulate between these layers of construction materials in the exterior building envelope to exit the system in a timely manner. (see detail 22) The design of the rainscreen drainage planes and drainage planes gives fluids (air and water) a more convenient pathway to follow past and away from the more vulnerable construction joints. (see detail 23)

No one can turn back those proverbial “hands of time,” and in the case of large dimension material panels used in the exterior building envelope, it’s neither possible nor necessary. It is possible and necessary that the construction industry understands that whenever a new material with either a new dimension or composition is introduced into any system, it may (and often will) have a negligible impact on the other materials used with it. We must focus on “holistic” building if we truly want to achieve “sustainable” buildings!

Weeps – The Why, When and Where

Weeps - The Why, Where, When

Published By: MTI | Date: March 2014 | Author: John Koester

Download Article

The MTI article “Weep Now or Weep Later” addressed the function (or in many cases the “dysfunction”) of various types of weep materials and devices. This article addresses the “why, where and when” of weeping masonry walls.

The why part is easy; it’s just a good standard practice to follow and not that expensive. The where part should be obvious – at the lowest point of a cavity or core – where the water is! The when part takes a little more thought. A general rule to follow is, “If there is a relatively open vertical void in the interior or the back side of a veneer (rainscreen) and it has a bottom, it needs to be weeped.

In reality most weeps are installed or not installed, and the masons don’t know (or care) why! Where the weeps are installed has virtually no reasoning, scientific or otherwise. And the when part seems to be “just as little as possible.”

So why is it that an inexpensive, relatively easy process that can lead to such serious consequences if not included in the exterior building envelope is so often done incorrectly or completely overlooked? The answer may be that it is so inexpensive and insignificant in appearance that it is easily omitted.

  • So inexpensive that no one spends much, if any, time talking about their importance.
  • So inexpensive that no one invests any time educating and training the industry on correct design and installation.
  • So inexpensive that no one has a vested financial incentive to explain their function and defend them in any forensic investigation of a premature failure of an exterior building envelope involving entrapped moisture.

In many cases involving premature failure of the exterior building envelope, where entrapped moisture was identified as the main contributing factor, the forensic investigator’s conclusions are “just plain wrong!” In too many of these cases, the failure of waterproofing components (roofing membrane, flashing system, waterproof coating, etc.) is incorrectly identified as the main contributing factor. However, the real culprit is often a poorly designed and/or incorrectly installed drainage system. Waterproofing systems exposed to long-term ponding water will not produce a positive outcome.

“Detailing” the Solution

The focus of this article is weeps and weep systems and the waterproofing materials that are used with them to create an effective moisture management (drainage) system for the exterior building envelope. It’s inconceivable that including an effective weep and flashing system can break the budget for a masonry wall, yet it happens all the time. So the explanation for the industry’s repeated failure to include them or to accept such poor design and materials must be found elsewhere.

The answer, at least in part, is that the industry just doesn’t know or understand how moisture impacts exterior building envelopes and the veneers that adorn them. If the industry doesn’t know the potential cost of neglecting this detail, why would they budget and pay for it? Another possible reason for reoccurring problems with weep details (or the lack thereof) is insufficient oversight; no one is watching! It is time for the weep issue to come to the forefront in the quest for more sustainable buildings. This issue is too important to the long-term viability of the building envelope to simply be an act of happenstance.

Creating a Moisture Management Plan

Any good moisture management design starts with a good plan of attack. This plan should start once there is a preliminary design. This is the first opportunity to understand the concept of moisture management “risk zones.” It’s also early enough in the design process to modify the design to avoid unmanageable “risk zones.” Moisture management “risk zones” are determined by a variety of factors.

  • The building site
  • Climate of site location
  • The structures orientation on the building site
  • The structure itself (multistory, low and sprawling, etc.)
  • Materials used in the exterior building envelope
  • Veneer materials (brick, stone, manmade, etc.)
  • Number of openings in the veneer and external building envelope (windows, doors, etc.)

All of these factors must be considered both separately, and collectively, to properly determine the moisture management “risk zones.” The details then need to be designed to manage or reduce the identified risks.

What constitutes a moisture management “risk zone?” It is a section of the exterior building envelope that has a specific, unique exposure to moisture. (see Sample Building) The moisture management risk can vary in intensity from very low to extremely high. One of the main reasons for identifying the various “risk zones,” and the degree of moisture management risk they represent, is to design the appropriate risk management detail. A second reason for this process is to understand and outline the boundaries of the risk zones to design details in a way that separates them from one another.

There are many examples of premature failure of the exterior building envelope that illustrate entrapped moisture has migrated from one location (zone) to another. This migration, along with the costs associated with premature failure, can be prevented with the appropriate detailing.

The process of determining moisture management “risk zones” can start at any part of the exterior building envelope. In most cases since moisture moves from a high point of entry to a low point in the exterior building envelope, starting at the top just makes sense. Although this article concentrates on the wall portion of the exterior building envelope, it is important to know that many serious wall moisture management problems are actually caused by roof leaks, both low-sloped and high-sloped; however, because of space issues that subject will be addressed in another article.

Sample Building

In some cases the determination process may be a two-step procedure: a determination of a “general risk zone” and a second determination of “associated moisture management risk zones” within the original identified “risk zones.” Examples of this two-step determination process include parapet walls and window openings.

The sample building is an example of assessing moisture management “risk zones” for the purpose of designing the appropriate flashing and weep detail to help modify the moisture management risk. The sample building has numerous identified moisture management “risk zones” on and in its exterior building envelope.

  • Parapet wall
  • A decorative cornice belt
  • Window openings
  • Door openings
  • Louver openings
  • Intersection of a top of a non-frost affected concrete stoop and masonry wall
  • Intersection at grade of a masonry wall and frost affected sidewalk
  • Intersection at grade of a masonry wall and landscaping

Details 1A & 1BRisk Zone #1 is an example of a parapet wall “risk zone” (See Sample Building and Detail 1A) with multiple associated moisture management details.

  1. Coping
  2. Roof flashing and counter flashing
  3. Transition point from bottom of parapet wall to top of exterior building envelope that encloses the interior spaces – “the decorative stone cornice band”

The coping on the parapet wall is the roof of the parapet and must be waterproofed. (See Detail 1B) Coping stones are one of a number of exterior building envelope details that has numerous responsibilities and are positioned, in many cases, virtually out-of-sight and out-of-mind. The intersection of the roof and parapet on the bottom back side of the parapet is another moisture management detail with numerous responsibilities. The roof flashing and the parapet wall counter flashing must be designed to be both a waterproof detail and a movement absorbing detail that can accommodate expansion and contraction of the roof assembly. (See Detail 1A)

Detail 2, Photos A & BThe point where the bottom of the parapet wall ends and the top of the exterior building envelope that encloses the interior spaces of the building begins is sometimes unclear. Risk Zone #2 is the top of the decorative stone cornice band. (See Sample Building and Detail 2) Do not be mislead by the term “decorative.” It is also a moisture diverting detail and a wall “roof” for the wall and windows below it. (See Detail 2)

There is an industry-wide misconception that patterns on the exterior of the building envelope veneers (stucco, wood, brick, stone, etc.) are simply decorative. In truth their primary function is protection. They direct moisture away from sensitive details such as windows and doors. (Picture A) In the past the construction industry understood this multipurpose concept and had the sense to make them both functional and aesthetically appealing. The current trend seems to concentrate solely on the aesthetic aspect. The unintended consequence of this singular focus is the creation of surface patterns (or details) that actually cause moisture management problems. (See Picture B)

Details 3 & 4Risk Zone #3 is the group of six windows on the second and first floors on the right and left sides of the exterior building envelope. (See Sample Building and Detail 3) In many cases windows or numbers of windows should be grouped into one “risk zone” because their moisture management details are so interconnected and interdependent; one moisture management risk zone with multiple, associated moisture management details! (See Detail 3)

Risk Zone #4 is the pair of louvers and windows on each side of the entryway. (See Sample Building and Detail 4) Obviously, louvers and windows are different, but the moisture management detail is virtually the same, and their proximity to one another joins them into one moisture management “risk zone.” In many circumstances the wall opening that is directly above another wall opening will have an impact on the wall opening detail below it even though they may be of different types. The explanation is obvious – “water runs downhill!” (See Detail 4)

Detail 5, Pictures C &DRisk Zone #5 is the arch above the front entry. (See Sample Building and Detail 5) The arch is probably the most misunderstood moisture management detail of all the wall-opening details. When I see weeps protruding from the radius of an arch, it is so ridiculous it almost makes me smile. However, there is nothing humorous about the construction industry’s lack of understanding when it comes to moisture management! (See Picture C)

If the weeps installed on the radius were to be functional at all, there would need to be an upturned stop flashing at that point of the arch flashing to stop moisture, and the weep would need to be installed at the bottom of the valley in the flashing. It would also have to have the same elevation in the masonry joint. (see Detail 5) The skill to execute this type of detail is difficult, if not virtually impossible, to find.

Detail 6Like many good practices and details in the construction industry, the moisture management detailing for arches has been lost to history. Arches have been in common use since the time of the Romans, and so has the moisture management detailing required to preserve them; however, most people today simply pass it off as decoration. The gaping mouths in the heads of animals and gargoyles that serve as column caps supporting arches on ancient and medieval structures are actually the weep exits (holes) for the arches’ moisture management system. (See Picture D)

Risk Zone #6 is the decorative band stone that separates the bottom of the first floor exterior building envelope from the garden level exterior building envelope. (See Sample Building and Detail 6) This veneer detail has a number of responsibilities. It is a moisture diversion detail that diverts moisture out, over and away from the windows and wall below it. (See Detail 6) This decorative band stone also has an aesthetic appearance aspect.

Details 7 & 8

Risk Zone #7 is the intersection of the vertical wall and the top surface of the non-frost affected stoop platform. (See Sample Building and Detail 7) This vertical wall veneer surface will be subject to water splash back from the top surface of the platform of the stoop. Also, various types of ice control chemicals (salts, deicers, etc.) may contaminate it, and snow removal tools (shovels, scrapers, etc.) may contract it. This wall detail needs to be durable, aesthetically pleasing and backed by a waterproofing system because it is an exterior wall system with an interior living space behind it. (see Detail 7)

Risk Zone #8 is the front stoop steps and stoop platform. (See Sample Building) The 7th and 8th risk zones are the perfect example of the interdependence of moisture management systems. In the case of the stoop platform and steps, the slope-to-drain of the surfaces and their ability to resist moisture penetration is absolutely critical. A detail that will allow for replacement of the stoop platform and steps without major impact on the veneer wall system is the appropriate design. (see Detail 7) This is an example of how a comprehensive understanding of moisture management risk zones influence the original building design and its detailing to allow for future maintenance, repair and replacement of the exterior building envelope components with the least amount of interruption to adjoining details.

In this instance, the stoop platform is the construction detail that has the most exposure to moisture and will, in all likelihood, need to be repaired or replaced before the other adjoining details. The band of stone at the bottom of the vertical brick wall should be more durable than the brick. It separates the edges of the top surface of the stoop platform from the brick veneer and diverts water away from the intersection of this moisture sensitive detail. (see Detail 7)

Risk Zone #9 is the set of two garden level windows on each side of the front entryway stoop. (See Sample Building and Detail 8) Window openings at this elevation on an exterior building envelope have a number of unique moisture management concerns. Their proximity to grade level and the moisture that may accumulate there is of real concern. The potential for splash up moisture is an additional negative. Designing/detailing the grade surface that adjoins these types of grade level windows is a very important factor that will play out in the day-to-day maintenance and their long-term sustainability. The other obvious concern with windows in this location is security. A damaged window is also not very waterproof. (see Detail 8)

Details 9 & 10

Risk Zones #9 and #10 are the two on-grade details that contact the bottom perimeter of the building on each side of the front stoop. (See Sample Building and Details 9 and 10) The grade surface on Detail 9 is a frost-affected sidewalk; the grade surface on Detail 10 is landscaping stone.

These two very different “on grade” materials need to follow many of the same rules of good moisture management.

  • They both need to maintain good slope-to-drain away from the structure they contact
  • Their top surface elevation must not interfere with the drainage “weeps” of other exterior building envelope components (these risk zones) and their movement up or down in elevation due to expansion or contraction of soils that support them (because of the wetting or drying of supporting fill material, or because of the freeze-thaw cycle in supporting fill material, or because of the characteristics of expansive soils that may be supporting) must be taken into consideration. (See Details 9 and 10)
  • These details cannot at any time, or for any reason, become attached to the structure they abut. The attachment and potential movement of these details will result in severe damage to the structure and the “at grade” details. (See Details 9 and 10)


The importance of identifying unique moisture management risk zones on and in the exterior building envelope is key to creating and maintaining a sustainable building. However, though these moisture management risk zones can be identified as separate and unique for the purpose of designing and detailing, they are not and cannot be disconnected from each other when it comes to moisture management. From top to bottom and from bottom to top, they all interconnect and impact each other. No good wall system can survive a bad roof and no good roof can survive a bad wall system; they support and protect one another. This is what holistic, sustainable building is all about – knowing that nothing is separate, all things are connected and nothing stands alone.

The Three Part Rule of Moisture Management

Three-Part Rule of Moisture Management

Published By: Masonry Magazine | Date: July 2013 | Author: John Koester

Download Article

The three-part rule of moisture management is "Get moisture off of, out of and away from a construction detail as quickly as possible!" However, we are left with the nagging questions: Off of to where? Out of to where? Away from to where? Answering these three questions is the really difficult part of the rule.Only a fraction of the liquid water involved will evaporate into thin air, and in some cases even then it can still have a negative impact on the construction detail.

Get Moisture Off of Construction Details

Figures A - C1 Let’s start with getting the water “off of” a construction detail. Obviously, there are hundreds and hundreds of details this applies to; however, let’s start with roofs. Roofs can be sloped to drain in many directions. (A) The roof style depends on numerous factors including architectural style, distance to be covered, budget, etc. Generally, for moisture management purposes, the more slope the better. The greater the slope (pitch) on a roof, the faster liquid water can run off. (B) This is important because the less time liquid water is on a construction detail (roof) the less the likelihood it will absorb into that construction detail. We should also reduce the number of projections or obstructions that are in the path of this draining liquid water. Anything that slows the flow of liquid water off of a construction detail such as chimneys or vent stacks increases the amount of time that liquid water will spend on the construction detail. (C) Once the water reaches the roof perimeter, where does it go? (C-1)

Figures D - F1A good rule to follow is to not allow it to come back into contact with the building or any other construction detail. (D) There should be a relationship between the depth of the overhang (eve) and the height of the wall from eve to grade. (E) This ratio is valid only up to a certain height.

Multi-storied buildings have other concerns with moisture on their exterior building envelope that deal with the variation of surface pressures on the exterior building envelopes of high-rise buildings. This eve detail is the most straightforward of all perimeter roof details. (F) Perimeter roof details that involve a gutter and downspout add many concerns; they complicate the detail and must be designed, installed and maintained correctly. Gutters and downspouts can easily trap debris, ice and snow; these obstructions slow down and even dam up liquid water. (G) These debris and ice dams have caused building owners and insurance companies hundreds of millions of dollars over the years.

Figures G - I1The best scenario for liquid water once it is off of a roof perimeter detail and headed downward is directly to a designed grade. (F-1) If it comes in contact with the surface of the building’s exterior wall or lands on another construction detail, there is more work to be done. (D) The construction details we are concerned with include other lower roofs and roof pitches, tops of doors, tops of windows, tops of walls, etc. The roof run off water from a higher roof adds a whole new dimension to the moisture management equation because it can be a very concentrated flow. When it lands on a lower surface, it can, over time, erode the lower construction detail. The roof run-off water from a higher roof delivered in a slow “drip, drip” fashion, creates a perpetually wet condition for the lower construction detail. This perpetually wet state is extremely undesirable from a moisture management standpoint. (H & I)

Though the amount of water may be small, the unchecked, constant delivery allows all the water to be absorbed into the construction detail. If liquid water flows from one roof to another and then another, moisture management becomes extremely difficult if not impossible. (I)

Get Moisture Out of Construction Details

Figures J & J1The amount of water entering a construction detail is certainly of concern; however, the amount of “time” that even a small amount of water is in a construction detail is also of concern. The extended “time” factor will allow moisture to absorb more and more deeply into the detail. Amount and time are negatives because they extend the drying cycle, possibly even into the next wetting cycle allowing the construction detail to be in a perpetually wet condition. This extended wet condition may also be subjected to a “freeze-thaw” cycling compounding the problem. The amount of time that moisture is in contact with a construction detail is, in many cases, even more critical than the amount of moisture involved.

It can also result in the much-publicized “mold” issue. Mold is, in many ways, like corn or soybeans; it needs a consistent, steady moisture supply. A construction detail that is persistently wet and has a growth supporting material (organic) in it or on it, will probably grow a very healthy crop of mold that is hazardous to the health of the building’s occupants. Designing a construction detail that allows the moisture that enters it to have a designed way to exit it is probably a good idea. (J & J-1) In fact getting moisture “out of” a construction detail is the “Law!” (2009 IBC R703.12.1.)

Get Moisture Away from a Construction Detail

Figures K - K2Once the liquid water is on the top surface of the surrounding grade, the third element of moisture management comes into play. We need to get the moisture that we have drained “off of” and “out of” the building, “away from” any and all construction details. Building sites must have a designed drainage plan. This drainage plan should be in place from the earliest stages of the planning phase; it should be rigorously maintained during the construction phase; and it should be continued throughout the building’s useful existence. Unfortunately, this is one of the most neglected aspects of good moisture management. If neglected there may be dire consequences because critical structural components of a building such as basement walls and footings, and their supporting soils may be compromised. (K)

The drainage plan begins with properly poured footings and correctly constructed and waterproofed foundation walls. A drain tile system should also be included. Once these items are in place, continual monitoring and maintenance is critical. Backfill and foundation support soils that are subjected to constant moisture will put unwanted stress on belowgrade construction details. In areas where expansive soils exist, or where very deep frost can occur, this variation in moisture content can be disastrous. (K)

Figure L - MLandscaping, both hard and soft, that is immediately adjacent to buildings, must be designed to compensate for fill disturbed by foundation excavation. (K-1 & K-2) If this run off water needs to be diverted around dwellings, the pathway swale needs to be a minimum of 15 feet away from dwelling and preferably hard surfaced. (M) Excessive moisture will also over-stress the moisture-resistant coatings and drain tile systems that should be a part of below-grade construction details. (L) The high moisture content of these soils will also intensify thermo-transfer characteristics of the backfill and support soils. Water and/or high moisture content materials transmit temperature better than air and dry or low moisture content materials.

Soil temperatures 42” below grade are consistently 520 - 540 Fahrenheit. When they are nearly saturated with water, they may not be cooler, but they will be able to transmit the 520 - 540 F temperature to the belowgrade construction details more efficiently. If the ambient temperature in the below-grade construction details cannot keep basement walls and floors warmed, and if they are constantly in a cool condition, the chances are that the surface temperatures of these foundation components may be at or below the dew point and condensation will occur. When water vapor condenses on a surface, or on other air particles, liquid water droplets form, and this can, and often does, create a “wet basement!”

By now it should be apparent that by not complying with the “away from” part of the rule of good moisturemanagement, a lot of really bad things can and will happen. Designing and maintaining a good drainage plan for a construction site is not easy, but it is well worth it. A construction site with a designed and maintained drainage plan is more efficient for everyone involved! A site that is allowed to turn into a “swamp” will regularly impact the site including the soils and the fill surrounding the building foundation, and that may have both short term and long-term negative consequences.


When it comes to managing moisture, it should be obvious that there are direct connections among all moisture management conditions and components. John Donne wrote, “No man is an island, entire of itself.” The same thing holds true for any construction component or detail. Very few, if any, features or factors of a construction project stand alone. There is a holistic relationship that exists, and the improper treatment or neglect of any one component will imperil the rest!

Moisture Management Strategies for a Second Floor Deck above a Living Space

Moisture Management Strategies for a Second Floor Deck Above a Living Space

Published By: The Construction Canada | Date: May 2013 | Author: John Koester

Good Moisture Management – An Overview

A comprehensive moisture management plan for any construction detail must include the following:

  • Moisture Resistant Materials (damp proofing, WRBs, waterproofing, etc.)
  • Slope-to-Drain (a designed elevation change to direct liquid water to a desired low point away from, off of and out of the construction detail)
  • An unobstructed pathway/void for liquid water to “quickly” exit the construction detail

Although these three points seem reasonable and straightforward, they are often ignored! One of the reasons may be that some professionals in the construction industry actually believe that there is such a thing as “waterproofing” and that nothing more is required. They believe this because there are hundreds of high quality moisture resistant products out there with thousands of sales people saying these products will waterproof something, anything and everything! Informed, experienced construction professionals that understand what waterproofing systems are capable of, use the phrase moisture management system (or plan). Waterproofing is easy to say, but true waterproofing is very hard to do. The manufacturer’s warranty offers an additional point of interest. It often specifies that the warranty will be made void if there is ponding water on their system. (This is a common clause in roofing system warranties.)

How Does Good Moisture Management Apply to Verandas?

Verandas (porticos) are commonly used as second story decks. If they are used as walkways to connect exterior doorways to connected rooms they are called a gallery, promenade or loggia. The characteristics that add degrees of difficulty to these moisture management systems are that they need to be durable for traffic bearing. In many cases there is an aesthetic requirement – people want them to be pretty! A common traffic bearing overlayment that would accommodate these requirements would be stone overlayments in various patterns. General descriptions of the construction details that make up verandas are as follows:

  • Three exterior insulated structural bearing walls that support the structural deck
  • An insulated structural deck
  • A waterproofing system on the top surface of the structural deck that may run down over the exterior face of the structural walls or terminate at the deck perimeter
  • A code-compliant perimeter restraining system (railing) of various types or parapet walls of various heights and designs
  • A support system for the stone overlayment that may include some type of pedestal paver system for each stone corner, a mortar bedding system, etc.
  • A flashing system where the veranda meets the exterior wall of the main dwelling • Slope-to-drain on the surface of the traffic bearing stone
  • Slope-to-drain on the top surface of the waterproofing material that is applied to the slope-to-drain top surface of the structural deck
  • An unobstructed pathway for the liquid water that may be present on the slope-to-drain top surface of the traffic bearing stone to run off the veranda
  • An unobstructed pathway for the liquid water that may be present on the slope-to-drain top surface of the waterproofed top surface of the structural deck to run off of and out of the mortar bedding or stone pedestal system

Drawing A, B1, B2No Task for Amateurs

It should be apparent by now that the design and execution of the construction phase of a moisture management system on a veranda is no task for the amateur or uninformed professional. There are several factors that add even more difficulty to this type of construction.

  • The top surfaces of these verandas may have accumulations of snow and/or ice on them for long periods of time. (A)
  • They may have other surfaces such as roofs that drain on to them. (A)
  • The interior living areas underneath are heated and/or cooled, and these extremes of temperature have to be accommodated within the insulated structural areas of the deck. (A)

Verandas have numerous critical construction details (previously mentioned), any of which if not properly designed, constructed and maintained, can cause serious moisture management problems. Some of the most common detail failures include:

  • Improper slope-to-drain on the top surface of the traffic bearing stone (B-1)
  • Improper slope-to-drain on top surface of the structural deck (B-2)
  • Inadequate waterproofing system on structural deck
  • Improper/inadequate pathway for liquid water that may accumulate on the top surface of the traffic bearing surface of stone overlayment system to run off
  • Improper/inadequate pathway for liquid water that may accumulate on the top surface of the waterproof surface of the structural deck to drain out of the detail
  • Improper/inadequate perimeter details for liquid water to flow off of deck surface (scuppers, downspouts, etc.)
  • Improper railing mounts
  • Improper/inadequate insulation of structural deck
  • Improper/inadequate venting of structural deck joist cavities

The slope on the surface of the traffic bearing stone is the first critical point. Slope-to-drain is commonly called out in inches-per-foot or fractions of inches-per-foot. One quarter inch-per-foot (1/4” per 1’) is the very minimum slope-to-drain that is acceptable for low slope stone surfaces. The distance that liquid water has to travel before it is away from, off of and out of a construction detail is also very critical. The greater the distance, the greater the chance this flow of water will be interrupted or slowed by some sort of obstruction (organic debris, snow, ice, etc.). Distance traveled is in direct proportion to time; the amount of time that liquid water is in contact with a construction detail is in direct proportion to the amount of water it may absorb. Also, the longer water is on, in or near a construction detail, the greater the chance it may go through a freeze-thaw cycle. It should go without saying this slope-to-drain should be diverted away from the main dwelling if at all possible. (C)Drawing C, D, E A second area of focus is the top surface of the structural deck. Unfortunately, this is one of the most overlooked and neglected aspects of good moisture management of verandas. The top surface should be sloped-to-drain a minimum of 1/4” per 1’ to at least match the minimum slope-to-drain of the traffic bearing stone; it could be sloped even more. Stone traffic bearing surfaces will rarely conform to the requirements of a barrier system. They will absorb moisture, and there will be voids/cracks in grouting mortar and bedding mortar. Moisture will ingress down to the waterproof system on the top surface of the structural deck. (C) With inadequate slope-to-drain on the structural deck, moisture will accumulate and pond. At best it will drain slowly. Long-term, continuous moisture presence in and on this construction detail will greatly increase the risk of a leak through the waterproofing system, accelerating the deterioration of the bedding system and stone overlayment. Dead level (or close to dead level) structural members with continuous loads on them do not remain dead level for long; they belly down. This is one of the lesser-known problems with inadequate slope-to drain or dead level structural decks. They are usually constructed with structural members like steel beams, concrete blanks, dimensional lumber, fabricated wood joists, etc. These structural members have crowns in them and are installed crown up. If they are supported dead level at each end, half of the structural deck will be pitched back toward the main dwelling. (D & E) An improper or inadequate pathway for liquid water to run off of the waterproofing system on the structural deck and out of the support detail for the stone overlayment is another point of concern. Water may want to run in a design direction with slope-todrain, but it will need a space (void) to run through. This drainage plane will be created by the height of the support pedestals in the stone paver pedestal system and by the drainage plane system installed under the bedding mortar of the stone overlayment system and over the waterproofing system. These drainage plane materials also act as a protection mat for the waterproofing system. The perimeter detail’s requirement for liquid water to flow off the edge of the sloped-to-drain top surface of the traffic bearing stone is key and can be made more complicated by aesthetic requirements. This water may transport varying amounts of impurities (soot, dirt, organic debris, and dissolved salt and minerals from the stone overlayment system. If this water comes in contact with the vertical face of the exterior wall, it will stain the wall. Besides the negative aesthetics that may result from this contact, there is the potential for structural deterioration of the vertical wall. Inadequate perimeter drainage detailing is the most common design flaw. The design and construction of these details conflict with the aesthetic appeal of the rooflines and face of the supporting wall, and designers are too restrictive with them. In doing so, they can be too small and too few to be functional (Pretty, but pretty wet!). The other most common detailing design flaw is that the required elevation stepdowns are not designed in the traffic bearing surface perimeters so the perimeter drainage detail material actually dams up a certain amount of water as it attempts to enter the detail. This very point can also be a material transition, material stress point. A material stress point and dammed up water reservoir + time = a water leak! A perimeter roof leak, more so than an in-the-plane roof leak, will probably become a wall leak too. (F-1, F-2, F-3, F-4)Drawing F1-F4 The perimeter drainage detail that allows the water that is on the waterproofed surface of the structural deck and in the bedding mortar of the stone overlayment system to drain is also critical. Good waterproofing practices require additional, stronger materials at points where the surface of structural details change (horizontal to vertical at the edge of structural deck). If this “making stronger” means adding layers of material, this elevation change created by thicker material has to be designed into the perimeter elevations of the structural deck. The design and execution of this construction detail will, in most cases, involve some type of skirt board or fascia board. (G-1, G-2, G-3) Drawings G1, G2, G3 HImproper or inadequate railing mounts are another common failure point. The structural people have done all their work to perfection; the waterproofing people have done all their work to perfection; the stonemason has done all his work to perfection and then the railing guy comes along and drills a hole (holes) through everything! Past studies have shown that 85% of all labor procedures conducted on waterproofing systems, including the installation of the waterproof system, are conducted by persons that do not understand waterproofing and are very seldom held responsible for their premature failures (e.g. electricians, plumbers, heating & air conditioners, railing installers, masons, sign installers, decoration installers, window cleaners, etc.) (H) Drawings I & JIn the case of improper or inadequate railing installation, the structural deck designer missed an important design requirement. The structural deck design should have had pedestal curbs built in and up past the top surface of the stone overlayment, and they should have been included into the waterproofing system. (I) The structural deck of a veranda has to be insulated, and the insulation material has to be kept dry. The insulation part is easy; the keeping it dry is not. The two main sources of moisture are infiltration of liquid water (a leak) and water vapor that is driven into the insulation from the interior living area where it meets a dew point and condenses into water droplets (liquid water). The types of materials used to construct the structural deck of a veranda are as numerous as the methods of how to best insulate them. There are, however, several best practice design points: (J)

  • A waterproof system to keep liquid water from entering from above
  • A structurally sound deck
  • A system to vent the open area between the bottom of the decking and top of insulation in the joist cavities
  • Insulation
  • A vapor retarding system on the interior walls behind the interior sheathing
  • A moisture resistant interior sheathing
  • A vapor resistant coating or covering on the exterior surface of the interior sheathing.

(There are many examples of structural decks that will not accept all of these systems such as poured concrete, solid concrete plank, etc.)


Decks above living areas (verandas) need to be designed and built with great care. In many areas they are becoming more common because of local zoning requirements (restrictions on hard surface landscaping that affect surface water runoff). They can be a design requirement; they can be beneficial; they can be very functional and they can last a long time (with proper maintenance) if they are designed and built correctly!

Weep Now or Weep Later

Weep Now or Weep Later

Published By: The Construction Specifier | Date: April 2013 | Author: John Koester

Download Article

“What people believe prevails over the truth.” Sophacles

Figure 1
Inset A. shows sash cord weep protruding from wall with no evidence of weeping. Inset B. shows weep hole with no evidence of weeping. Efflorescence indicates some moisture has leaked out through mortar joints. Weeps are also incorrectly placed - they are not at the lowest point of the wall!

Introduction Thirty years ago I applied for, and was issued, my first patent, a utility patent for a weep system. The main “claim” of the patent was the forming of the bottom side of a bed joint of mortar to create tunnels or channels into the cores or cavities of masonry walls. In the process of researching information for the patent’s content, something became very apparent; many of the masonry industry’s accepted “rules of the road” or “standard practices” for weeping a wall had no scientific basis!

The spacing of weeps 16” or 32” or 48” on center is one example of a common practice without scientific support. Obviously, this spacing pattern is modular, but modular and moisture-management have no scientific correlation that I can find. There may be code that specifies a certain spacing (International Residential Code R703.7.6 Weep holes and International Building Code 2104.1.8 Weep holes), but that doesn’t mean there is research to support that code. Some things are just done long enough that they become standard practice. If it was done in the past, it must be right, so why change it?

With the old weep technology and its spacing, the water got out of the cavities and cores of masonry walls; however, it wasn’t necessarily through the weeps, it wasn’t necessarily all the water, and it wasn’t necessarily a fast process. (see #1 above and insets A. and B.) Moisture management in masonry walls, or in any other construction detail, is about getting the water away from, off of, and out of the construction detail as quickly as possible. The amount of “time” that moisture is in, on or near a construction detail is in direct proportion to the amount that will be absorbed into the materials that compose the construction detail.

Figure 2

What is a Weep?

Weep: Openings placed in mortar joints of facing material at the level of flashing, to permit the escape of moisture.” (from MCAA. Masonry Training Series, Vol. 1. Dubuque: Kendall/Hunt, 1996. Print.)

 There is a need to repeat the obvious; a weep device should create an opportunity for the liquid water that has drained down to the top surface of a flashing to exit the core or cavity of the masonry wall on the top surface of the flashing. (see #2) Unfortunately, the masonry industry has in some cases incorrectly adopted the use of head joint air vent material and devices as weeps. (see #3 & 3A) A number of unfortunate conditions have occurred because of incorrect uses of materials and devices.Figures 3 - 5

  • Many of these air vent devices are not dimensionally correct to accommodate the potential variations of a first course bed joint of mortar and masonry unit. (see #4)
  • The non-voided portion of the bed joint of mortar becomes a dam that causes water to form a reservoir at the bottom of the cavity. (see #5)
  • Installation of this type of material, even if it has been field-fabricated to the right height, is labor intensive and a cumbersome, multistep process. (see #6)

Figure 6

  1. The bed joint of mortar needs to be spread. 
  2. A masonry unit (brick) is laid. 
  3. Displace mortar to allow for weep placement. 
  4. The air vent material is placed. 
  5. A bed joint of mortar needs to be respread in front of the air vent material. 
  6. A masonry unit (brick) is laid to the air vent material and into the bed joint of mortar. 

Figures 7 & 8The appropriate detail for a masonry air vent and a masonry weep would look like this. (see #7) The weep holes are at the lowest point of the masonry wall (and cavity) and are spaced 10.5” apart to improve the mathematical chances that one of these weeps will be at the lowest point of the masonry wall (and cavity) where the water is. The masonry wall air vents should be spaced every third brick head joint, one to two courses above the bottom of the cavity and above the weeps. They should also be a course below the top of the vertical height of the flashing that is mechanically fastened to the backup wall. (see #8)

This detail provides excellent weeping capacity and potential air intake to improve airflow in the cavity of the masonry wall. The positive outcomes include:

  • Improved chances for pressure equalization of the cavity or core of the masonry wall with the pressure on the exterior surface of the masonry wall (the rainscreen). This is desirable because a pressurized cavity (or core) may move air to depressurize, moving moisture-laden air (water vapor) deeper into the exterior building envelope. (i.e. the scientific principle of high pressure to low pressure to equalize pressure)
  • Improved airflow in the core or cavity of a masonry wall if equal air intakes and air exits are provided at the top and bottom of the wall. This will have “some” positive impact on the masonry wall’s ability to dry out. It should be emphasized, however, that the ability of masonry cavity airflow to dry out or remove moisture “is extremely limited!” Do not expect this airflow to effectively remove or alleviate any type of ponding water condition. That is the job of a well-designed weep system.

Figures 9 - 12A weep detail that is commonly utilized on lintels and shelf angles is an open head joint. (see #9 & #10) This detail has the potential to provide both weeping capacity and airflow. It also doesn’t have the related bed joint of mortar problems because the first course of brick is usually laid dry on the flashing material that covers the lintel or shelf angle and waterproofs the bottom of the cavity. If it is utilized with a bed joint of mortar, there is a chance the bed joint of mortar directly below the open head joint will not be raked clean of mortar and that amount of the bed joint of mortar will dam up water flow out of this detail. (see #11) In other cases, the bed joint of mortar is left in place because raking it out is not architecturally appealing because it breaks the coursing lines of the bed joint. (see #12)

Figure 13-18One of the first weep details that was commonly employed was the sash cord or “rope” weep. (see #13) In some cases this detail was expanded with sections of the sash cord laid in the cavity and then extended through the wall, usually at a head joint. In other cases the sash cord was fastened vertically up the backside of the cavity. In yet other cases, it would be pulled out of the wall leaving a hole through the head joint or bed joint of mortar. How and when these sash cord sections were placed or embedded in the bed joint of mortar impacted whether or not they had any weeping capacity.

If they were placed on the flashing and the bed joint of mortar was spread on top, the finished detail looked like this. If the bed joint of mortar was spread and the sash cord section was laid or embedded into it, the finished detail looked like this. (see #15) The theory was that the cotton sash cord would “wick” water out of the core or cavity and dry the units. However, if there is one takeaway from this article, let it be this, “Do not get into a wicking contest with masonry mortar or masonry units!” How can a sash cord of less than 3/8” in diameter compete with the wicking capacity of all the masonry units and the bed joint of mortar?

Over time, the cotton sash cord was replaced with synthetic cord that had even less wicking capacity. Moisture management is about the amount of “time” moisture is in, on or near construction details, and a wick is not quick! Many have seen an example of a rope weep that has moisture stains around the outside end of the cord; it appears to have moisture “weeping” from it. What is really happening is that a small amount of moisture is actually exiting the cavity through small voids in the bed joint of mortar at the 5 o’clock and 7 o’clock positions on the bottom radius of the sash cord; moisture is not wicking through the cord material! (see #14)

A variety of tube weeps have also been introduced to the masonry industry. (see#16) These tube weeps are usually pieces of plastic pipe cut to length. The installation procedure is virtually the same as the sash cord material and so are the shortcomings. Even when the tubes are installed correctly on the top surface of the flashing, the wall thickness of the weep, though small, is still a water dam. Why would water elevate itself enough to get up and over the edge of the tube wall when it can just wick itself into the mortar and the other components that make up this portion or an exterior building envelope? To improve on a bad idea, the masonry industry has taken two dysfunctional weep products and created a tube weep with a sash cord in it! (see #17) And as difficult as it is to grasp, there is actually a “slope-to-drain weep tube sash cord product.” (see #18) Understanding how this “weep concept” could be correctly installed so that it could function is beyond comprehension! How can the construction industry be so uninformed that it would even entertain the notion that these products could actually weep a wall?

Another important message is that, “Weeps do not work until the water gets to them!” It is critically important that the cavity or core (the void behind the veneer) is open and clear of obstruction to allow liquid water to move from a high point of entry to the lowest point of the cavity or core, which is the top surface of the flashing.

Figure 19In the past attempts to produce this part of a masonry veneer wall has been the responsibility of masons. The results have varied from good open and clean cavities or cores to ones that are very close to being poured solid. Predictable, high quality results are required to effectively manage moisture. The introduction of a device to maintain this void (a rainscreen drainage plane) has improved the required predictability. (see #19)

Renowned architect R. Buckmaster Fuller said, “People should think things out fresh and not just accept conventional terms and the conventional way of doing things.” This line of thinking is certainly relevant when it comes to conventional weeping products and practices.

This article has presented concepts and techniques that go against the grain for many in the masonry industry; however, if adopted and practiced, the outcome is a more sustainable building envelope and a more aesthetically pleasing facade.


Drainable is Sustainable

Drainable is Sustainable

Published By: Masonry Magazine | Date: December 2011 | Author: John Koester

Download Article

Most exterior surfaces of a vertical wall system do allow some moisture to penetrate deeper into the exterior building envelope. Why do building professionals allow this; don’t we have adequate waterproofing systems? Part of the answer is “Of course we know and of course we do, but that isn’t the hole/whole story!” The hole/whole story, the more complete story, is that some exterior building surfaces of the exterior building envelope are responsible for more than just moisture management. These responsibilities include aesthetics, structural support, signage support, mechanical support and protection (veneers acting as shields). In addition to all these responsibilities, they also have to manage moisture! So the hole/whole story is a little more complicated! As part of the process of moving forward, let’s take a look at an example of a typical exterior wall (exterior building envelope). Obviously, there are many types of wall systems, but let’s use this one (Figure 2.) to simplify the discussion as much as possible. Figure 2

Rainscreen Components

The Rainscreen is the most exterior surface of an exterior building envelope. It is the first surface that has the potential to change the exterior environment to satisfy a desired interior environment: wet to dry, hot to cool, cold to warm. It can be constructed of various materials including brick, stone, stucco, steel, wood, glass, plastics, and fabrics. The next section, the Rainscreen Drainage Plane, is the space from the backside of the rainscreen to the front surface of the moisture resistant material. It can be either a wall design feature (such as a space) or a product. The third section, the Water Resistive Barrier, can be a waterproofing product (usually a sprayed or rolled on chemical compound) or a weather-resistant material (two layers of construction paper or a building wrap). It can also be both. The final section, the Structural Wall, can be composed of a variety of materials including wood or steel studs, cmu or poured concrete. Figure 3In most cases there is a requirement for insulation. It comes in many forms and can be placed in various locations in this detail. It is an extremely important and extremely complicated character in the hole/whole story and must be included in the moisture management equation. (Figure 3.) All forms of insulation involve unique moisture management issues that are beyond the scope of this article; however, they must be seriously examined when constructing a moisture management plan for the rainscreen building envelope.

Sustainable Building and Moisture Management

Sustainable building isn’t possible without moisture management. For those forced to live or work in a building without it, life becomes a health and safety nightmare. Bold statements, but totally supportable. According to the HUD’s Path Project, “Moisture, in all of its physical forms, is commonly regarded as the single greatest threat to durability and the long-term performance of the housing stock. Excessive exposure to moisture is not only a common cause of significant damage to many types of building components and materials, it also can lead to unhealthy indoor living environments. A long list of serious adverse effects can result from moisture problems in houses. There is wide agreement that successful management of moisture in its various forms is essential for houses (buildings) to be durable, safe and energy efficient.” In its 2004 report, the Path Projected listed the following outcomes of uncontrolled moisture in the building envelope:

  • Decay of wood and corrosion of metals
  • Infestation by termites and other destructive insects
  • Negative impacts on indoor air quality
  • Growth of mold, mildew and other biological contaminants
  • Reduced building material strength
  • Expansion/contraction damage to materials
  • Reduced thermal resistance of wet insulation
  • Premature failures of paints and coatings
  • Damage to building contents
  • Negative effects on building aesthetics

Enter the key phrase sustainable rainscreen building envelope into Google and you will get more than 18,000 results, including MTI’s “Drainable is Sustainable” presentation delivered at last fall’s technical meeting of the Sealant Waterproo ng and Restoration Institute. A key point of the presentation is that a moisture management solution for the rainscreen building envelope requires a systemic/holistic approach. There is no single magic bullet; it takes a well-thought-out, coordinated system of products and processes designed and implemented by a team of professionals working collaboratively at every stage of the project to reach a successful outcome.

Motorcycles, Rainsuits and Moisture Management

Motorcyclist rainTo illustrate the importance of a coordinated system in moisture management, I’ll use the analogy of a motorcyclist riding towards an approaching storm. It’s a nice sunny day, so I decide to go for a motorcycle ride. Being an experienced motorcyclist, I always have raingear in my saddlebags because it’s summer and anything is possible! As I move through the countryside, I notice that the sky is darkening and a storm is imminent so I pull over and put on my rain suit. In a matter of minutes, the rain starts. It’s light at first but soon becomes heavy, and it’s coupled with a driving wind. Rain is forced around my windshield and into my eyes greatly limiting my ability to see the road. Water cascades off my helmet and runs down the back of my neck soaking my shirt. The water on the highway flies upward leaking into my boots through the seams and around the tongue. To make matters even worse, it’s a hot, humid day so beads of condensation start to form on the inside of my rain suit making for an increasingly miserable rideObviously evenen though I thought I was prepared for rain, I hadn’t looked at all possibilities.” Even though I had a collection of items designed to keep me dry, I hadn’t fully thought through the outcome, and I hadn’t properly combined the items into a functioning system. If I had used goggles or a helmet with a visor, I could have seen the road better. If I had used the hood on my jacket and worn it under the helmet, I wouldn’t have gotten rain down my back. If I had used a rain jacket with vents, air could have moved around inside the system and reduced the condensation. Finally, had I worn rain boots with my rain pants lapped over the top of the boots and fastened snugly, I wouldn’t have gotten wet from the water spraying up from the road. So what can be learned from this analogy about the importance of a system in solving the building envelope moisture management problem? Hopefully, it’s that simple solutions don’t always work. As much as the motorcycle rider would like to just throw on a waterproof jacket and waterproof pants and be off again, it just doesn’t work. It takes many products, put on in the right order and at the right time, to create a positive result. We need to look at how many factors are in play and then employ several moisture management solutions as part of a system to solve the problem.

The Importance of Holistic-Systemic Building

This same idea of a coordinated, multi-component solution can be applied to the people designing, specifying and constructing a building. Gone are the days when designers, specifiers, and contractors could successfully do their jobs in a vacuum. There are just too many new products, processes and complex codes for the “Lone Ranger” approach to work. Everyone must collaborate and communicate if a sustainable, healthy building is the goal. This brings us back to our hole/whole story concept. Merriam-Websters Dictionary defines holistic as: “relating to or concerned with wholes or with complete systems rather than with the analysis of, treatment of, or dissection into parts.” Knowing how each product used in the construction of the building reacts with the rest of the products is critical! Is it compatible with the rest of the system, or does it create unintended consequences? Have the parties designing, specifying and installing the products looked at all the possible outcomes of the each procedure and each product with the rest of the system? That’s the “whole” part of the concept. The “hole” part of the concept refers to the importance of drainage in an effective moisture management solu- tion in the rainscreen building envelope. The normal interpretation of a hole in a building envelope is a nega- tive one. However, all building envelopes leak. Moisture can enter from the outside in multiple ways including wind-driven rain and cracks in the veneer. Moisture can enter from the inside in the form of condensation. So if we know water is going to get in, how is it going to get out? WeepsIn many places, drainage of the exterior building envelope is a code requirement. Section 1403 Performance Requirements (International Building Code 2009, pp. 277-278) states: “1403.2 Weather Protection. Exterior walls shall provide the building with a weather-resistant exterior wall envelope. The exterior wall envelope shall include ashing, as described in Section 1405.4. The exterior wall envelope shall be designed and constructed in such a manner as to prevent the accumulation of water within the wall assembly by providing a water-resistive barrier behind the exterior veneer, as described in Section 1404.2, and a means for draining water that enters the assembly to the exterior.” Subsection - 1b of the National Building Code of Canada 2005, Volume 1 states: “The second plane (the drainage plane) of protection shall be designed and constructed to i. intercept all rain and snow that gets past the first plane (the veneer) of protection and, ii. effectively dissipate any rain or snow to the exterior”

Real Waterproofing Involves Real Drainage

Moisture DamageIn his August 2010 article Putting in Holes to Stop Leaks, Brett Newkirk wrote, “A wise Canadian once said, ‘It is amazing how many leaks you can stop by putting holes in a building.’” The holes referenced are weeps, but not just any weeps. Gone are the days of the “wicking” rope weep or the weep tube. If these old-style weeps worked at all, it was because some water leaked out of the moisture voids next to them and not through the weep itself. Many times, these antiquated weep devices weren’t even placed at the lowest point in the wall. An effective weep must be placed at the lowest point in the wall (the bed-joint-of-mortar). Weeps also need to be place frequently to be effective. The channeled weeps in Figure 6. above are placed 10” on center. Over the last 20-30 years we have experienced a myriad of moisture-related problems in the building envelope. The increased use of rainscreen technology by designers has seen more than its share. There are many reasons for moisture problems in the rainscreen building envelope. Some of the most frequent issues include:

  • Tighter building envelopes increased mold and rot problem
  • Many modern materials created unintended moisture barriers
  • Increased insulation led to condensation problems

The Three Key Components

Figure 10Figure 11Figure 11Figure 12

Rainscreen walls with a wide variety of veneers are sustainable when combined with the right moisture management system. This effective moisture management system includes three key components. First, there must be a space from the backside of the rainscreen (veneer) to the face (exterior surface) of the WRB. (The minimum depth is still being debated, but should be at least 1/8”. In Canada 10mm is required.) This space must be uninterrupted, predictable, constant and stable, and the materials used to create it should have very low absorbency. Second, we need to dump the water (weep holes) out of the rainscreen drainage plane at every possible opportunity. Water should be dumped at transition details (e.g. brick to stucco, siding to brick or stucco, etc.), projection details (e.g. windows at top, windows at bottom) and wall terminations (e.g. bottom of wall, top of wall). The final component is air pressure control. A well-designed rainscreen drainage plane system helps maintain pressure equalization. It lessens the chance that high-pressure air, contaminated with moisture, will move from high pressure to low pressure and deeper into the building envelope. And with venting at the top and bottom of the wall, air ow may assist in drying the building envelope. (Figure 12.) Lu Bu Wei, a Chinese philosopher wrote, “It follows, then, that all things work together...The Sage examines them in order to observe their similarities.” In other words looking for one simple solution to preventing mois- ture problems in something as complex as a modern building is unrealistic. There are too many things that come into play: materials used, the laws of physics, the people involved, location/climate, the many systems brought together in the building. To reach a true “waterproofing” result we must work together as a team and we must create the right moisture management system. And that’s the hole/whole story! Weeps draining brick wall

Rainscreen Drainage Planes vs Furring Strips

Rainscreen Drainage Planes Vs Furring Strips

Published By: Construction Canada | Date: December 2011 | Author: John Koester & Mark A. Johnson

Download Article

The construction industry and more specifically, the building envelope sector of the construction industry, seems to embrace the status quo with exceptional tenacity. There are obvious reasons for this unwillingness to change. Manufacturers of products currently utilized in building envelopes don't want to see change, and many tradespeople don't want to learn new techniques.

“For time and the world do not stand still.  Change is the law of life.  And those who look only to the past or the present are certain to miss the future.” John Fitzgerald Kennedy The idea that “Change” is a law of life has been proven true again and again since the dawn of time.  In our own lifetime think how much technology has changed the way we live in just a few short years.  And yet we seem so slow to change.  Many of us actually dread the idea!  Our present habits are like the comfortable old jeans we refuse to throw out despite the stains and holes.  Resistance to change is as predictable as the knowledge that change is inevitable. The construction industry and more specifically, the building envelope sector of the construction industry, seems to embrace the status quo with exceptional tenacity.   There are obvious reasons for this unwillingness to change.  Clearly, manufacturers of products currently utilized in building envelopes don’t want to see change unless they have another product that fits with the new way of doing things.  Also, many tradespeople don’t want to learn new techniques when current practice has served them well for so long.  There is a long list of players who could be negatively impacted by the implementation of new technologies, new materials and new techniques including the shipping and storage industry, unions, contractors, raw materials producers, architects, specifiers and codes officials.  Building is a complex process, and there are countless individuals and organizations involved.

Forces of Change

It is unfortunate that “change” is often accompanied by the words “forced to.”  While force may bring about superficial change, it rarely engenders quality of change.  One of the more common forms of force used to change the construction industry is through codes.  The dictionary defines the word codes as “any set of standards set forth and enforced by a local government agency for the protection of public safety, health, etc., as in the structural safety of buildings.”  Codes require the building industry to conform to a “minimum standard.”   It is the very least you can do without breaking the law and being subjected to fines and/or imprisonment.  There’s probably little realization among the general public that buildings are being constructed with the goal of meeting a “minimum standard.” Economics is the other factor that brings about change.  If a product is cheaper, smarter and sexier, and if consumers become aware of it, they’ll demand the new technology.  Industry will also shift to new technologies if they see an economic and/or marketing benefit.  For example, how many products have suddenly become “green?” The focus of this article is the adoption of modern rainscreen drainage technologies by the construction industry as a solution to the entrapped moisture problem.  The issue was first addressed in Canada in the last part of the 20th Century because widespread failures of the exterior building envelope were occurring.  Building scientists discovered that a space between the backside of the veneer and the front of the backup wall could alleviate the problem, and code was written to force this change. In 2005 the National Building Code of Canada was modified to include Section, Minimum Protection from Precipitation Ingress.  This section states, “an open drainage material, not less than 10mm thick and with a cross-sectional area that is not less than 80% open, is installed between cladding and the backing, over the full height and width of the wall.”

Furring Strip Drainage Systems

Example AContractors began using wood furring strips to create this space to allow moisture to drain down and out of the building envelope and to equalize air pressure between the front and the back of the rainscreen building envelope.  If installed correctly, they provided this required space behind the rainscreen for moisture to move out, and they allowed for air pressure equalization.  As time passed, new types of materials (plastic, metal, etc.) began to replace wood furring strips. In most furring strip applications, additional materials are required to complete and support the construction of this rainscreen drainage plane detail.  These supporting materials include some type of semi-rigid moisture-resistant panel or roll stock material used in combination with construction paper as a slip-sheet. There are several inherent problems with this type of rainscreen drainage system.  The two that are probably the most negative are:

  • Too many components (cost issue)
  • Too labor-intensive (cost, time, and complexity issues)

Another factor that negatively impacts this system is its violation of the most basic principle of moisture management; it fails to provide a means for moisture to effectively exit the building envelope.  (Example B)   The International Building Code, Section 1403.2 states, “The exterior wall envelope shall be designed and constructed in such a manner as to prevent the accumulation of water within the wall assembly by providing…a means for draining water that enters the assembly to the exterior.”  Section 703.1.1 of the International Residential Building Code affirms this point. The three required components of a well-designed moisture management system to stop moisture penetration include:

  • Moisture-Resistant Materials (flashings, coatings, WRBs, etc.)
  • Slope-to-Drain (to direct moisture out of the construction detail)
  • Predictable Open Channels (pathway to the exterior of the building/building details that allow moisture an unobstructed pathway out of the construction detail)

Example BThe furring strip rainscreen drainage system pictured in Examples A and B interrupts moisture at the building paper slip-sheet surface installed in front of the semi-rigid asphalt board but doesn’t provide a designed detail for this obstructed moisture to drain to the exterior (See Example B – Top Down View).

  1. Sheathing
  2. Fastener
  3. Intermediate Furring
  4. Building Paper
  5. 3-Ply Semi-Rigid Asphalt Board
  6. Building Paper - Slip Sheet
  7. Stucco Lath
  8. Three-Course Stucco
  9. Stucco Cracking
  10. Moisture

The Waterproofing Issue

The required drainage that must be provided in front of a moisture “water stop” has a long history of being misunderstood and is often improperly detailed or even omitted in the design and construction of the exterior building envelope.  The root cause of this problem may be the construction industry’s unrealistic comfort level with the idea of “waterproofing.”  The reason for waterproofing’s preeminence can be at least partially explained by the petro-chemical industry’s rapid growth resulting in large volumes of byproducts in need of disposal (e.g. coal tar pitch from the coking of coal, asphalt from the distillation of petroleum, etc.).  When these byproducts were found to be excellent waterproofing materials, a market was needed; enter the construction industry! Prior to this period, about 125 years ago, various types of metals such as copper and lead, and some tree pitches and animal fat impregnated fabrics, were the only moisture-resistant materials available.  The construction industry’s only real moisture control was slope-to-drain.  Slabs and boards of semi moisture-resistant material were installed shingle-fashion on roofs with high pitches; they were also  installed vertically on walls.  Coal tar pitch and asphalt changed all that and led to developments like “low slope” or “flat roofs.”  The petro-chemical industry modified and improved on these original materials and also added many high-quality synthetic waterproofing materials.  These abundant, high-quality waterproofing materials distracted the construction industry’s attention away from the need for drainage. Example C

The Need for Drainage

With the avalanche of building envelope failures over the last two or three decades, the need for the inclusion of drainage in the building envelope moisture control equation has become increasingly clear.  Furring strips were an early answer, and were, at least for a time, an imperfect solution.  However, the placement of the furring strips created a new problem.  The early use of furring strips to create a drainage plane looked something like Example C. The furring strips, attached at each stud location, pushed against the scratch coat of mortar bellying it out and allowing the furring strip to come in close proximity to the stucco lath.  This created a much thinner layer of stucco at each furring strip and often led to stress cracks in the three-course stucco. (See #8 Example C) Example DIn an attempt to improve this application, an additional furring strip was installed midway between the 16” on- center furring strips. (See #3 Example D)  This alleviated some of the bellying/cracking problem, but it also created a new issue.  The labor forces would occasionally fasten the expanded metal lath to this nonstructural termination (the intermediary furring strip); this resulted in more extreme cracking. Excessive, uncontrolled cracking in the rainscreen of the exterior building envelope is unsightly, and it creates an opportunity for excessive moisture to egress into the rainscreen and potentially deeper into the exterior building envelope.  To make matters worse, the cracks were occurring at fastening points.  This fact potentially allowed egressing moisture to have a direct pathway along fastener shanks and into the stud cavity (See #5 & #6 Example E).  All because the labor force incorrectly used non-structural details as attachment points. Example EIncorrect placement of fasteners that penetrate to the backside of the backup wall sheathing and on through to the backside of roof sheathing does cause real “leak” issues.   However, the moisture patterns seen on the backside of the sheathing may not be from egressing moisture!  Instead, they could be a water pattern caused by the melting of frost balls or the run off of condensation.  What is really happening is that the shanks of the misplaced fasteners may not be pathways for liquid moisture; rather, they are pathways for cold temperature.  The result is the points of the misplaced fasteners are cold enough to create dew points that in turn allow for condensation in the form of frost balls or water droplets (See #4, #5 & #6 Example F).  So the old technology seems to have quite a bit of room for improvement.Example F

The New Technology

The new technology that is attempting to improve the rainscreen drainage detail is the use of “mat” materials.  Most of these mats come in the form of roll stock, and they are created with various manufacturing procedures and materials.  The primary manufacturing procedures and materials are as follows:

  • Continuous vacuum molding of various types of plastic sheet roll stock material creating a variety of shapes or raised patterns and dimples in the material.  A second manufacturing process involves adhering a synthetic fabric to the tops of the raised pattern.  (Example G)
  • The extruding of various types of plastics into filaments into a variety dimensions then compressing and organizing them into continuous mats of various thickness and widths. A second manufacturing process involves adhering a synthetic fabric to one or both sides of this entangled filament mat.  (Example H)
  • The extruding of various types of plastics into filaments of different dimensions and compressing them into a sheet. This sheet is then formed into a variety of corrugated patterns.  (Example I)
  • The forming and perforation of a plastic roll stock material into a variety of corrugated patterns and thicknesses. A second manufacturing process adheres a synthetic fabric to one side.  (Example J)

Examples G - JThese four manufacturing procedures are used to create six of the major product lines that represent the new “mat” rainscreen drainage plane technology in North America.  They differ from one another in drainage efficiency, compressive strength, and ease of installation.  What they all bring to the construction industry, and specifically to the exterior building envelope segment of the construction industry, is ease of installation and in most cases, a more predictable cost-effective rainscreen drainage plane.  When choosing which one of these new rainscreen drainage plane technologies to use in your next project, select the one that best suits your veneer/rainscreen type and one that has a CCMC evaluation number.