Protecting the Top of Walls in Straw Bale Homes
The Problem for Straw Bale Homes
I recently received an email from a couple who own a straw bale home and are experiencing moisture issues at the top of their wall. It makes my gut clench getting an email like this!
How did this happen? It was due to a leaky gasket surrounding a vent pipe penetrating the roof. Water was making its way into the house by draining through a gap between the pipe. (The gasket was meant to prevent this! Don’t worry, I’ll give you a solution below.)
The water then traveled along the roof rafter and deposited onto the top of their straw bale home’s wall. They noticed the issue when they saw wetness in the plaster at the top of the wall.
Unfortunately, this story is all too common. I've heard of numerous situations where moisture finds its way through the roof and onto the top of straw bale walls.
This is undesirable because moisture can migrate into the center of the bales. When moisture gets into the center of a bale, it's very difficult for it to dry out quickly, potentially leading to mold and even rotting.
A Simple Solution
While there are many ways this type of situation can occur and just as many ways to fix it, I want to share a low-cost, simple technique. This method minimizes the top of the wall's exposure and protects it from unfortunate roof leaks and moisture damage of this nature with a secondary line of defense.
The technique I recommend employing during construction is adding a weather-resistive barrier (WRB) on top of the wall. This barrier is secured to the top of the bale stop, box beam, or underside of the roof rafters.
What is a Weather-Resistive Barrier (WRB)?
A weather-resistive barrier is a material designed to protect building components from water infiltration while allowing water vapor to pass through. This vapor-open quality is crucial for straw bale construction, as it allows any moisture that does enter to escape. This key feature prevents trapped moisture that could lead to mold or rot.
An excellent example of such a barrier is the SOLITEX MENTO 1000® from 475 High Performance Building Materials. This type of WRB is specifically designed to be highly water-resistant while remaining breathable, making it ideal for straw bale construction.
How to Stop Moisture On Your Straw Bale Home
Materials needed:
Vapor-open weather-resistive barrier (such as SOLITEX MENTO 1000®)
Fasteners (appropriate for your specific wall construction)
Sealant (compatible with the WRB and wall materials)
Basic installation steps:
Measure and cut the WRB to fit the top of your wall.
Secure the WRB to the bale stop, box beam, or underside of roof rafters.
Ensure the WRB overlaps the edges of the wall slightly.
Use compatible tapes or sealants to seal all edges and penetrations to prevent water ingress.
Benefits of the Weather-Resistive Barrier in Straw Bale Homes
The idea behind this technique is to protect the center of the bale from direct moisture penetration while allowing any trapped moisture to escape. The WRB sheds water to the edge of the bales. Once at the edge, the plaster absorbs the moisture and indicates a leak.
The quicker a leak can be recognized, the faster it can be fixed. Moisture diverted to the edge of the wall also has a better chance of drying out quickly.
The vapor-open nature of the WRB is crucial because it allows the wall to "breathe," preventing moisture accumulation within the straw bales. This characteristic is essential for maintaining the long-term integrity of the straw bale wall.
No one likes a leaky roof; however, this simple technique can help prevent costly damage and provide peace of mind that the top of your wall has a secondary level of defense against roof leaks while still allowing for proper moisture management.
Conclusion
Implementing this vapor-open WRB technique during the construction of your straw bale wall can save you from potential headaches down the road. It's a small investment of time and materials that can significantly extend the life of your wall and protect it from unforeseen moisture issues. For those building or planning to build with straw bales, consider incorporating this method into your construction process for added protection and peace of mind.
Bale on,
Timbo Scursso
Ps. Have questions specific to your build? 100% normal. Take advantage of my years of experience in design-building straw bale homes to shortcut your learning curve > Learn more at Get Expert Support.