Better Brick Mortar Control is Better Moisture Control

Published By: MTI | Date: December 2016 | Author: Tyler LeClear Vachta

Cavity masonry construction is rooted in a theory of moisture control by draining water to the exterior.

Mortar still clogs the cavity
Mortar still clogs the cavity, just higher up. Drainage and ventilation are limited.1

Mortar Deflection Device Pitfalls

Mortar deflection devices claim to hold mortar above the weeps, and most accomplish this. However, the problem is just moved up the wall. The mortar dams up the cavity,  limiting drainage and ventilation. Cavity masonry construction must not simply hold the mortar above the weeps but rather ensure a clear moisture drainage pathway behind the entire veneer.

Cavity masonry construction must not simply hold the mortar above the weeps but rather ensure a clear moisture drainage pathway behind the entire veneer. Mortar that bridges the masonry cavity can lead to moisture transfer and degradation of materials.

MTI's Mortar Control System addresses these concerns and provides proven protection for wall systems.

Mortar Control with Sure Cavity™ and Cavity Weep™

Comparing Drainage and VentilationMTI’s Mortar Control System features two components: the Sure Cavity Drainage Plane and the Cavity Weep weep system. Sure Cavity features “True Channel” drainage technology with clear, rigid channels that quickly and effectively drain moisture and ventilate the cavity. The Sure Cavity ensures ventilation across the entire backup wall that cannot be clogged with mortar squeezings.  Sure Cavity's mortar-blocking fabric ensures that the drainage channels stay clear and is permeable so that moisture can drain and the cavity can dry. A course of Sure Cavity angled at the bottom of the wall system provides an extra level of protection by holding mortar droppings away from the weeps and preventing mortar from bridging the cavity.

MTI’s Cavity Weep creates four weep holes every 9.5 inches and drains directly on the flashing, the lowest point of the wall system. Cavity Weep's translucent plastic blends with mortar for a superior appearance.

MTI’s moisture management systems protect sensitive wall components and reputations.

Sure Cavity and Cavity Weep form a system that meets code standards 2015 IRC R703.1.1 Water resistance and 2015 IBC R1403.2 Weather Protection.

Features and Benefits

Mortar blocking fabric Maintains a clear drainage path, prevents mortar bridging, integrated insect barrier
Rigid, not fluffy Ease of installation, reducing labor costs
15.75” wide One size fits any cavity
96% pre-consumer recycled plastic Eligible for LEED points

Brick Mortar Control Detail Drawings

 

Brick Mortar & Moisture Control Products

Sure Cavity Rainscreen Drainage PlaneCavity Weep System

 

Design for Better Drainage. Build Sustainably.

Call 1-800-879-3348 to Order

 

1 Photo source: Laska, Walter "Proper drainage for weep holes", The Aberdeen Group, 1992. Publication #M920313

Gutting Brick Walls Post-Flood: Repair Recommendations

Rainscreen & Weeps Post Flood Retrofit

Note: The most updated flood retrofit information can be found at MTIdry.com/rebuild

Published By: MTI | Date: August 2016 | Author: Tyler LeClear Vachta

Flood waters recede, walls are gutted. How do you reduce the impact of future flooding and build a wall that performs well? 

As homeowners return to their homes after the devastation and flooding they are finding that some of worst damage is "hidden" within the walls of their homes.  The combination of trapped moisture and warm temperatures can lead to serious mold issues within a few short days.  Given that mold can have severe negative health impacts on homeowners and their families, it's important that any remediation/renovation efforts addresses the immediate existing mold AND minimizes the impact of water infiltration in the case of future flood events.

With this goal in mind, here are some recommendations on how to ensure that your renovation/remediation project delivers a result that is capable of quickly draining moisture, provides proper structural integrity and resists mold formation. Creating a drainable, dryable wall with water tolerant materials is an economical way to reduce the impact of future floods and achieve a higher performing building enclosure. In addition to using materials that can simply be washed down after a flood event a good system addresses concerns about moisture, structural strength, and thermal performance.

Moisture Concerns

Floods are not the only moisture concerns that walls face. The reality is that no veneer (brick, stone, siding, stucco) keeps out all moisture. The small amount of moisture that gets past it needs to be drained and dried or it can lead to dangerous mold and damage to building materials. A continuous, vented rainscreen air gap behind the exterior is a best practice approach to preventing incidental moisture issues. The rainscreen gap created by Sure Cavity is an integral component of the drainable, dryable flood resistant wall. In a future flood the Sure Cavity will allow the exterior wall to dry out.

Structural Considerations

Most framed exterior wells have plywood, OSB or gypsum sheathing to resist racking, but once flooded these water sensitive materials are removed from the inside. Replacing the sheathing from the inside is an impractical retrofit, but 2lb density closed cell spray foam can be used in the stud cavity to resist racking in the wall assembly and provide a water tolerant insulation.

Addressing Mold

Mold is a serious health concern in flooded areas that requires proper personal protective equipment and mitigation. Paper faced drywall, wood based materials and other organic materials are food sources for mold and need to be removed after a flood.  Apply a paint-based fungicide to walls, studs and insulation surfaces to kill mold and pre-treat for mold in future floods.

Doing the Retrofit – An Overview for Brick Walls

Brick Rainscreen Retrofit with Retrofit Brick Ties Detail Drawing
Download the Detail Drawing

Consult the detail drawing and video with this article. Always consult with building codes officials before beginning any construction project.

  1. Treat the stud cavity for mold and allow to completely dry.
  2. Preserve any flashings that are present and clean out weep holes. If weeps aren’t present drill them through mortar joints at the lowest point in the wall to drain water from the rainscreen. Leave brick ties in place, and reinforce with expanding spray foam. If brick ties are missing, install MTI Retrofit Brick Ties.
  3. Create a rainscreen drainage and ventilation gap on the interior with the Sure Cavity™ rainscreen drainage plane. Install with fabric facing the installer, back-wrapped at the bottom to create a bugscreen, and shingle-lap fabric in subsequent courses. The Sure Cavity can be attached directly to the brick wall or to the studs.
  4. Apply 2 inches of 2-pound density closed-cell spray foam insulation between the studs and over the Sure Cavity. Apply a preventative fungicide to the spray foam and stud cavity.

In a future flood these drainable, dryable, water-tolerant materials can remain in-place – just wash down and replace the flooded interior drywall. For next steps on rebuilding a flood-resilient interior finish view the wet-floodproofing recommendations below.

To order Sure Cavity for your restoration and learn more about resilient rebuilding
Call MTI at 800-879-3348 or Contact Us Online

FAQ - Frequently Asked Questions

Note: The most updated flood retrofit information can be found at MTIdry.com/rebuild 

Are There Other Considerations For Floor Recovery?
Where Can I Find Other Resources For Flood Recovery And Mold Removal?

This guide is NOT comprehensive.  Take a chance to learn from people who have been through floods before. Following Hurricane Katrina and other flooding events the Lousiana State University Extension and LaHouse Homeowner Resource Center have partnered with Building Science Corporation to develop and disseminate resources for homeowners. Browse the LaHouse Homeowner resources.

Will This Prevent My Home From Flooding In The Future?

No. The rainscreen approach is a building science best practice to prevent entrapped moisture problems under normal conditions. Many brick veneers were constructed without the proper air gap behind the brick for drainage and ventilation. Without a rainscreen air gap normal weather conditions lead to a buildup of moisture in the wall system and structural deterioration as well as mold issues.

How Can I Reduce The Impact Of Future Flooding?

Using this rainscreen retrofit technique along with "wet floodproofing" approach for your interior renovation will result in a wall system that is drainable and dryable. Using flood hardy materials reduces the time and resources required to rebuild after a flood.

Wet Floodproofing Resources

Do I Need To Plug Weep Holes During a Flood?

No. Unless your home is a submarine the exterior materials along with doors and windows are not watertight and will succumb to the flood waters. Standing water in contact with brick walls (or other veneers) will inevitably enter the structure and plugging weep holes will not improve the situation.

What Types of Insulation Can I Use?

Consider using insulation that is water tolerant, such as closed-cell insulation in spray foam or rigid foam panels. Closed-cell insulation will not absorb water and may not require removal in a future flooding event.

Flood Clean-Up – Including Mold Control

Getting to the Bottom of Moisture Management

Getting to the Bottom of Moisture Managment

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

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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 wiseGeek.com, “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)

Conclusion

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.

Weeps – The Why, When and Where

Weeps - The Why, Where, When

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

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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)

Conclusion

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.

Weep Now or Weep Later

Weep Now or Weep Later

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

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“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.

 

Moisture Management of Parapet Walls

Moisture Management of Parapet Walls

Published By: The Construction Specifier | Date: September 2011| Author: John Koester

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Parapet Walls – What Are They Good For?

Parapet walls perform a number of important functions:

  • They can be designed in various shapes to create a desired façade
  • They can be designed to hide roof top equipment (AC units, etc.)
  • They help prevent roof edge blow off by diverting air flow up, over and away from the roof edge.
  • They can be a stable termination point, for roof edges and flashings.

However, even though parapet walls perform a number of important functions, they are moisture management headaches! The phrase ‘Out of sight out of mind” is, unfortunately, the rule of the day with construction details that are not easily accessible. Parapet walls fall into this category. The required timely maintenance is neglected because of this and regrettably, the need for maintenance becomes apparent only as a result of a failure such as a leak. On top of this, parapet walls have a rather rough life since they are subjected to wind, dramatic temperature changes, moisture from three sides and roof system stresses. The result is a construction detail that is both neglected and abused.

The answer to the question “Why do parapet walls fail?” seems obvious. The solution is just as obvious – design them to be better and maintain them properly. Drawings 1 & 2

The most fundamental rules of moisture management “Keep moisture away from, off of and out of a construction detail” and “Move moisture away as quickly as possible” always apply. However, two additional practices should be employed. First, use good moisture management design and identify and isolate the moisture risk zones in such a way as to separate high risk from lesser risk.

Like all structures a parapet wall suffers the fate of its roof – the coping. Failure of the coping is closely followed by wall and interior failure. (See Image 1)

First Moisture Management Opportunity

Of all structural components, the exterior building envelope (roof and walls) is the first opportunity for moisture management. The roof of a parapet wall is the coping and like other roof systems, there is a wide range of roofing styles and materials. So designing a maintainable coping system for a parapet wall and maintaining it properly is the starting point for designing and maintaining a parapet wall.

Like other exterior building envelope walls of the past, most parapet walls were solid masonry. As the construction industry’s need for more economical wall systems came about, cavity wall and thin veneer stud walls became the norm, and with the changing construction details came new and unexpected challenges. However, one thing didn’t change – the “environment” that parapet walls have always faced.

Parapet walls come in a variety of shapes and configurations: stepped, sloped, flat, and arched. There are also height variations and combinations of these configurations. (See Image 2) Image 3

Regardless of the configuration, they all have top surfaces. How this top surface is addressed can depend on a number of factors (building type, architectural style, building materials, etc.). However, since the top surface of a parapet wall is the roof of this construction component, it must be detailed accordingly. It must be waterproof or at least highly moisture resistant. How waterproofing and how moisture resistant depends on how much moisture is going to come in contact with the top of the parapet and in what form (rain, snow, ice, etc.). Of course there are many other environmental factors to take into consideration (wind loads, temperature fluctuation, etc.).

This decision making process is complicated when climate sensitive architectural styles are imposed into alien climates. (Example: Southwest/Adobe into high moisture Northeast U.S. locations) (See Image 3) The architectural style requires one look and climate conditions demand another. The moisture management compromises that are required to accommodate these architectural styles, in some cases, are building envelope disasters. Drawing 4

Designing High-Quality Parapet Walls

So how do we design and construct a high quality, maintainable parapet? We start by identifying its moisture management risk factor and that is easy. It is a very high-risk moisture management construction detail with unique moisture management provisions required. The more difficult decision of a designer is where does a parapet wall begin and end? If you are standing on the roof of a building, identifying where a parapet wall begins and ends is easy. If you are standing on the ground looking up at the exterior of a building, the point where a parapet wall begins and ends is not so obvious.

Once this designation has been made, the next decision is how to isolate this high moisture management risk zone from the other details that make up an exterior building envelope. We can do this in a number of ways. (Veneer surface patterns; veneer materials, etc.) No matter how it is accomplished, a type of water stop should be employed. (Example: a through wall type of flashing system/water stop)

Moisture Moving Upward

Drawing 5Intuitive thinking tells us we only need to manage moisture moving from a high point to a lower point in this construction detail. But the reality is that we also need to be concerned about moisture moving up into the parapet from construction details that are located below the parapet. That’s why we need a water stop. The parapet wall and the exterior walls that enclose the interior space (living area) of a building exist in two very different environments.

What makes their environments unique is the fact that the parapet wall has no direct temperature source from the interior of the buildings (neither hot nor cold) while the exterior walls that enclose the interior spaces do. Along with the temperature source difference, there is also the moisture source difference. The exterior walls that enclose the interior spaces may source moisture via vapor drive. (See Image 5)

What is initially thought to be a leaky parapet or roof-flashing detail may well be water vapor that has moved up the cavity of the exterior building envelope, into the cavity of the parapet wall where it is cooled. The condensates then run back down the cavity and into the other exterior building envelope details.

Identify and Isolate Parapet Detail

Identify and isolate the parapet wall detail from the exterior wall detail that encloses the interior spaces and identify and isolate the parapet wall from the building roof detail. (See Image 6) Drawing 6Once the parapet wall identification-isolation process is finished, we can begin designing a high quality maintainable parapet wall. Focus on the following components (top to bottom):

  • The parapet roof (coping) – Zone 1
  • The parapet wall – Zone 1
  • The bottom of the parapet wall – Zone 2
  • The intersection of the back side of the parapet wall and roof perimeter flashing detail – Zone 3

A well-designed coping on a parapet wall should look like this to best manage moisture. Unfortunately, good moisture management design is not always totally compatible with desired architectural styles. So we compromise, but only a little. Good slope to drain on the top surface of a coping is an absolute must. Any amount of standing/ponding moisture, in any form (snow, ice, water), is a pending moisture management failure for these reasons:

  • This moisture can find its way deeper into the coping detail and cause deterioration.
  • This moisture can find its way through the coping detail and cause deterioration of other parapet wall and roof flashing materials and details (See Image 7A)
  • Moisture can cause excessive stress on coping materials, expansion and contraction stresses from freeze/thaw cycles.
  • This moisture can sustain distinct temperature zones that will add stress to the coping detail

Drawings 7A-CGood coping overhang from exterior surface of parapet wall with a well-designed drip edge allows the moisture that runs off the top surface of the coping and down the side surface of the coping to drip freely from the coping and away from the wall surface of the parapet. This helps prevent moisture deterioration of the parapet wall in the following ways.

  • A well-designed overhang allows run off moisture to drip free off and away from the surface of the parapet wall
  • The drip edge directs moisture off the edge of the over hang and prevents moisture back flow back to the surface of the parapet wall (See Image 7B – Good Design and Image 7C – Poor Design)

Drawing 8 Good coping anchorage is a must. Air movement/wind can be extremely volatile at this location of the parapet. Building details that are not structurally sound cannot be maintained to manage moisture. (See Image 8 Inadequately Designed Coping Detail)

Environmental Stress

Environmental stressors (wind, temperature etc.) were mentioned earlier. Environmental stressors are very real, and they can damage or deteriorate coping materials. What is less obvious is that they can, over time, deform various types of metal coping. One of the more common examples of this is the concaving of metal coping. (See Image 7A)

When sheet metal is bent and formed into a desired shape, stress is built into the metal part and over time, the temperature cycles from hot to cold or from cold to hot allow a releasing of this built-in stress. In this case the sheet metal part is the coping that is trying to return to a flat sheet metal. In many cases this change in shape results in a concave cupping of the top of the metal, this creates a ponding configuration in the coping.

Wind is another stressor, creating movements of other components of the parapet wall and adjoining exterior building envelope details (Roof details etc.) This added movement could deform seams in the metal coping creating openings in the waterproof system. Any available water can then leak into the building envelope.

These environmental stressors can also negatively impact other materials (natural stone, manmade stone, bell tolls, etc.) that are used to create coping.

The design task is to create a coping that is strong, yet flexible enough to allow for expansion and contraction. Copings are truly working, moving construction details and like all mechanical designs that move under stress, they need to be examined occasionally for wear. They need to be maintained!

Drawing 9 Drawing 10

Adding Slope-to-Drain

When designing a construction detail to efficiently manage moisture, the more slope to drain the better (except when the slope to drain draws moisture from one construction surface to another. This can result in the lower construction surface being constantly wet or flooded. (See Image 9) Unfortunately, this is a somewhat common occurrence on sloped parapets. In many cases the moisture on the top surface of the sloped parapet coping has a tendency to run down the length of the coping instead of off the edge of the sloped parapet coping. This occurs when the overall slope of the parapet is greater than the slope on the top surface of the parapet coping. (See Image 10)

Related Drip Edge and Flashing Issues

Misunderstanding of how a drip edge works on the bottom edge of a sloped parapet coping can result in a similar condition. (See Image 11A)Drawings 11A & B This can also occur on the bottom edge of a cap flashing when a cap flashing is used to protect the top of a parapet wall when installed under a porous coping stone. (See Image 11B) The body of a parapet wall should incorporate the same good drainage design and details of other walls of the exterior building envelope.

Interior Moisture Management System

The interior moisture management components of a parapet wall should include the following:

  • A water stop/through wall flashing at the lowest point of the parapet wall
  • A well designed weep system at the lowest point of the parapet wall (on the top surface of the flashing)
  • A designed detail that allows moisture that makes it through the veneer / rain screen to drain from a high point of enterance to the lowest point of the parapet (the top surface of the flashing) and out of the wall through the weep system. This vertical void is called a rain screen drainage plane in thin veneers and a cavity in brick or other masonry veneers and also a core in concrete masonry unit (CMU) single wythe walls.
  • Structurally stable parapet wall; a structurally unstable construction detail cannot be successfully maintained.
  • The top of the rain screen drainage plane, cavity or core should be vented if at all possible. (See Image 12)

High Parapet Wall Issues

Drawing 13High parapet walls create real challenges for designers and maintenance personnel. There are numerous legitimate reasons for this type of extreme construction details (signage on the parapet façade, business theme’s, and covering large roof units etc.) but they are not easy to make structurally sound or to maintain. (See Image 13)

The intersection of the backside of the parapet wall and the roof perimeter flashing detail is a complicated, highrisk construction detail. It is always prudent to follow the moisture management rule of identifying and isolating high-risk moisture management details from lower risk moisture management details. In this case it is an absolute must!

So how do you design an effective moisture management system for this intersection of two very high-risk moisture management construction components? You keep the connecting detail very flexible. This can be accomplished with a lapping type of design (cap flashings, counter flashings type of detail) or a very flexible perimeter flashing system that bridges this connection. (See Image 11)

The exact design that connects the parapet wall and the roof system will vary with the type of roof configuration and type of roofing materials, but the concepts do not. The moisture management bridging of the intersection of parapet walls and roof systems is one of the critical design efforts; the other is the connecting detail. The connecting details ranges from nailed or bolted right together to barring on with a slip plate type of detail to a structurally detail completely separate. (See Images 12A-D) This wide range of connecting details will deter the moisture management type of bridging detail and flexibility should always be top priority.

Good building envelope moisture management, it’s all about the details! Drawings 12A-D