I have consulted with my friend and colleague on the East Coast, Laura Calfayan, owner of Calfayan Construction, Inc. For many years, CCI has been doing award-winning historical preservation and remodeling projects in the Philadelphia area. In the last few years, they have added a spray foam insulation service for their clients, using AirTight Spray Foam. I thought they would be the perfect source of good information for you, and Laura?s answer follows:
It seems your main goal is to insulate your roofline with an eco-friendly product. Our homes lose much of their heat in the cooler months through the roof, and the reverse occurs in the warmer months. To prevent this, you can insulate from the interior or?if your roof is flat?you can insulate from the exterior.
For interior applications you could use an open-cell or closed-cell spray foam. However, the tin ceiling will need to be removed. The application is not an injection procedure; these foams are applied directly to the underside of the roof sheathing with a large applicator gun. A good craftsman should be able to carefully remove the tin ceiling without causing damage by nipping the heads off the nails. When replacing the ceiling, they'll want to use tin nails and you may need to touch up the paint. But this is a small price to pay compared to the unbeatable benefits of foam insulation.
The instructions on some open-cell applicators say that you can inject the product, but I would not recommend this. Due to the foam?s high expansion rate, the risk of damaging the ceiling is great. There is an injection foam available, but the manufacturer doesn?t recommend using it in horizontal applications due to the water in the agent.
If the roof is flat, an exterior application might be your best solution. A closed-cell roofing foam can be applied with an acrylic coating on top. With only 1.5 to 2 inches of foam paired with an acrylic coating, a monolithic seal can be achieved. This is an extremely reliable solution that can last the life of your home. This seamless, lightweight coating not only provides significant insulation value, it can also stop the possibility of leaks. And foam roofing does not interfere with the installation of solar panels.
A few words on open-cell versus closed-cell foam: Open-cell foam was designed for soundproofing and packaging. It expands 100:1, has some insulative qualities, and is rated a green building product. Its R value is 3.5 per inch. Open-cell foam is not a moisture barrier and can contribute to mold growth.
Closed-cell spray foam, such as the AirTight Spray Foam that my business uses, is a well-rounded product that offers added benefits beyond those of open-cell foams. It is the most versatile, energy efficient insulation available. A modest estimate of its R value would be 6.5 per inch, which is about twice as high as any other insulation, including open-cell. Closed-cell foam expands up to 30 times its liquid volume to seal all cracks and crevices; it adds tremendous structural rigidity and creates a total air and vapor barrier. At just two inches, closed cell foam can stop 200 degrees of heat.
Whether you choose to insulate from the interior or the exterior, I strongly recommend closed-cell foam.