TECHNOLOGY DEPARTMENT
Basement Wall That Forgives So You Can Forget BY DOUG TARRY
ROXUL insulation products will not soak up moisture the way fiberglass insulation will, creating a more forgiving basement wall system.
A
s a residential contractor for many years, I have come to accept that basement walls are always going to be susceptible to moisture, as, aſter
all, they are built underground. ROXUL insulation products are ideal in this environment, since they will not soak up moisture the way fiberglass insulation will, creating a more forgiving basement wall system.
Tis was never more apparent than when we were pre- paring a home for closing in late 2010. Having installed the new building code-required insulation system for exterior basement walls, I was surprised to receive a call from my site superintendent indicating that there was water on the basement floor.
We were confident that our exterior concrete wall moisture management detail was correct, so we took a close look at the interior wall system. We found no moisture on the polyethylene vapor barrier—as you might see in the summer—but when we continued to pull the wall apart, we found that there was water forming on the house wrap and against the concrete foundation wall. Te insulation we used was saturat- ed and sagging. Water was also forming at the belt or rim joist and running behind the wall.
A tale of two walls Further research revealed that walls have a split per- sonality, depending on the season. According to our Building Science advisors, moisture tends to flow from wet to dry and from warm to cold. Tis means
that the warm, moist air of summer wants to go from the outside into your basement, which explains why we might see moisture on the vapor barrier. However, in colder months, the process is reversed. We were already building a very tight home with full-height basement insulation, and we were concerned that we might be susceptible to mold formation in the wall.
We needed to design a basement wall insulation detail that addressed wintertime vapor issues, as well as our mold concern, and decided to completely change how we build insulated basement walls. Our concept was to keep the wall warm so that vapor would not form, and, in case there was still moisture present, use ROXUL products that would not soak up that moisture.
Beginning at the belt, we started using spray-foam to reduce leakage, especially at penetrations. To protect, it we added ROXUL R23 (U.S.) 5.5-inch bat insula- tion, which has a Class ‘A’ fire rating. We changed the botom plate to pressure treated lumber and installed ROXUL 1¼” thick ComfortBoard IS R5 behind the studs and used ROXUL R15 (U.S.) 3.5-inch Com- fortBat in the wall. Tis system resulted in an R20 (U.S.) wall, which allows moisture to flow through without trapping it.
Subsequently, we have worked closely with ROXUL in two of our energy-efficiency research houses to devel- op an R22 code equivalent system, achieved by using ROXUL 1½” thick ComfortBoard IS R6 behind the studs, along with the R15 ComfortBat in the walls.
Doug Tarry is the Director of Marketing for Doug Tarry Homes, a company that has been building homes in the St. Thomas, Ontario area since 1954. Doug Tarry Homes has won multiple awards at the local, provincial and national levels, including Builder of the Year.
20 create | A REMODELING RESOURCE FROM NARI METRO DC
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