When thinking about the best approach towards insulating a home, many people immediately think of closed-cell foam. While the structural properties of closed-cell foam make it ideal for some applications, it is not always the best choice available.
Often, contractors spray closed cell foam over the rim joist and sill plate areas of the home (the wooden framing directly above the foundation wall) to insulate and seal off air leaks. While this application sounds good to homeowners, this common practice is actually a grave error that can lead to serious mold problems.
Moisture in the soil surrounding a home’s foundation naturally moves from wet to dry environments via capillary action and vapor drive. Therefore, water is literally sucked into the wood sill plate and joists via the porous concrete foundation. This would not be a problem if this moisture could continue its migration and evaporate. But closed-cell foam seals the wood so that it cannot breathe. As a result, moisture is trapped within and begins to do what it does best – rot the wood framing of the dwelling. This has serious implications for the stability and safety of the home along with becoming the source of mold formation.
Also, people tend to put too much emphasis on R-value when measuring the energy-saving thermal efficiency of foam; the higher, the better. So comparing a closed-cell R-value of 7 per inch to the typical R-4 open-cell measurement seems like a no-brainer. However, unlike open-cell foam that remains flexible, closed-cell foam becomes brittle over time to the degree that it can come away from the foundation and rim joist area (due to the natural expansion and contraction of the home’s wood and concrete) breaking the air seal. This is an important consideration for insulating efficiency. Therefore, a flexible open-cell insulation product provides a permanent air seal and may actually out-perform closed-cell foam.
Some manufacturers may claim that open-cell foam is not to be trusted because when submerged it absorbs too much water – unlike closed-cell foam. Yet there is another significant side of the story: open-cell foam products do not hold onto water. Therefore, they dry quickly and return to their original condition without warping, and full effectiveness is restored.
Open-cell foam has proved itself to be an important ally when building “green” healthy homes. The insulation product makes dwellings more energy efficient, while also protecting indoor air quality. As a result, the debate often won by closed-cell advocates is largely becoming a moot point when considering the health advantages and efficiency of open-cell foam.
