There are those who will swear that spray foam insulation is the panacea for energy efficiency in home construction. Most of these people want to sell you spray foam insulation. We use spray foam insulation in most of our custom homes and in some remodeling projects. We think that it is a very effective product in the right application, even though it has some significant negative issues. Spray foam insulation, when installed properly, can do a great job of not only insulating but also air sealing a house. Air sealing is at least as important as insulating. It is the air sealing that makes spray foam insulation in some applications worth the extra money that it costs. Cellulose insulation has about the same per inch R value as Icynene the most commonly used spray foam insulation in residential construction.
The problems with spray foam insulation are its cost, its production releases ozone depleting gasses and it has potentially harmful off gassing. For these reasons we tend to only use it on the underside of roof decking to put the thermal envelope and air barrier at the roofline. Many building scientists will tell you that you can create the same result with other products, which we believe…as long as testing is done soon after application. We do not feel that other types of insulation suspended from the rafters will maintain their insulative value over time. The roof line is the most important point of insulation and air sealing.
We use advanced framing techniques that minimize lumber and thermal bridging through the frame of the house. We are content to use dense pack cellulose insulation in the walls to achieve the same level of insulation as is achieved from spray foam. Cellulose insulation is made from recycled paper. To get a high level air seal we pay greater attention to the details of air sealing in the framing, application of the moisture barrier and drywall. These details can create an envelope that is just as tight as a complete spray foam envelope.
These techniques are key to achieving energy efficiency in new homes and remodeling. Using these methods allows for a significant reduction in air conditioning and heating loads. But they achieve an envelope that is so tight that mechanical venting is required. When possible, we use an energy recovery ventilator to maximize efficiency.