Rainscreen & Weeps Post Flood Retrofit
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.
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.
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.
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
- Treat the stud cavity for mold and allow to completely dry.
- 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.
- 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.
- 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.
FAQ - Frequently Asked Questions
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
- Low Country Rx: Wet Floodproofing (JLC)
- BSD-111: Flood and Hurricane Resistant Buildings (Dr. Josepth Lstiburek - Building Science Corp)
- Wet Floodproofing: Reducing Damage From Floods (LSU Ag Center)
- Wet Floodproofing Requirements - Technical Bulletin 7-93 (FEMA)
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.