Posted on: 30 August 2016
Spray-foam insulation has become one of the go-to ways to insulate an attic. It provides a superior R-value compared to traditional fiberglass batts (3.5 to 7 per inch for spray foam versus 2.2 per inch for fiberglass) that doesn't deteriorate over time. Still, recent reports of roofs facing rotting and moisture problems have called the use of spray foam into question. Will using spray foam really hurt your roof?
Two Types of Foam
To better understand the problems that can arise from using spray foam, you have to understand the two types of spray foam that are used: open cell and closed cell. When spray foam is installed, it uses a polymer and a foaming agent to bubble and expand. In open-cell spray foam, the air bubbles are broken, and open air provides the insulation. In closed-cell foam, the bubbles are solid and have no breaks in the foam bubbles.
This means that closed-cell foam is not just a great thermal barrier; it also forms an amazing vapor barrier as well. Open-cell foam, because of the holes in the cells, does not provide a vapor barrier. And that is what causes the problem.
In any rotting situation, you have moisture that is trapped against the wood and can't evaporate. With open-cell insulation in your roof in some climates, that's what happens. The moisture generated in your home rises and gets trapped in between the insulation and the roof. This moisture can't evaporate because there's no way for it to get through the roof on the shingle side and evaporate. If you live in IECC climate zone 5 or higher, you need to use closed-cell foam or a vapor retarder with open-cell foam.
Fixing the Problem
There are two ways to prevent this issue from happening. The first is to use closed-cell insulation only. Unfortunately, that can cost more than people want to spend right away. Another way is to seal the attic so it is airtight. This means that no moisture-laden air can get into the attic to work its way to the roof. The last solution is to condition the attic. This means running a dehumidifier or an air conditioner in that space.
In conclusion, if you're wondering if spray-foam insulation can damage your roof, the short answer is yes, spray foam can damage your roof if it's improperly installed. However, with proper installation, spray foam can and will save you money on your heating and cooling bills. For more information about what is right for your particular situation, consult a roofing contractor near you.Share