Q: Some builders and designers shun certain types of insulation because of their potential to damage the environment. What are the environmental tradeoffs involved in selecting insulation and why are some builders “foam free” advocates?
A: Life was a lot simpler when we could select insulation solely on the basis of how effectively it stopped the flow of heat. The higher the R-value, the less heat would sneak through a wall or a roof and the more comfortable the occupants would be.
That’s still true. The R-value of any given insulation is an important consideration. Building assemblies with higher R-values require less energy to heat and cool, so some builders and designers lean heavily toward the types of insulation with the highest available R-values. This list includes several varieties of foam available in sheet form—expanded polystyrene (EPS), extruded polystyrene (XPS), and polyisocyanurate. In addition, there are two types of spray polyurethane foam—open- and closed-cell—that are applied as a liquid. They quickly cure into a solid mass and are often used in exterior walls and roofs.
Foam insulation tends to have relatively high R-values when compared to other materials. XPS, for example, has an R-value of 5 per in. when manufactured, and some types of closed-cell spray polyurethane foam have R-values of greater than 7 per in. All of these options look better than some of our old standbys, such as fiberglass batts with an R-value in the neighborhood of 3.5 per in.
Some manufacturers have been careless or misleading with their R-value claims, and there are building scientists who would like to junk the metric altogether. The R-value of polyiso declines in cold temperatures while other types of insulation show one R-value at the time of manufacture and another a few years down the road as the insulating…