UPDATED on May 22, 2015
Many green builders want to build a foam-free house — that is, a house without any rigid foam insulation or spray foam insulation. The reasons behind this desire vary: some builders dislike foam because it is manufactured from petroleum; some because of off-gassing worries; some because of foam’s relatively high embodied energy; some because of the negative environmental effects of the blowing agents used to make foam; and some because they prefer to use natural building materials like straw bales.
I believe that the use of some types of foam insulation is often defensible, and that there are valid counterarguments to many anti-foam positions. However, I’m not going to debate these issues in this article. Instead, I’m going to provide recommendations for those who want to build a foam-free house.
To build a foam-free house, designers and builders can choose from a variety of foam-free approaches to accomplish the following tasks:
Some of these tasks — for example, insulating an attic floor — are easy. Others — for example, insulating a slab on grade — are more challenging.
As long as the rafters are deep enough, vented cathedral ceilings can be insulated with a wide variety of fluffy insulation materials, including cellulose, denim batts, mineral wool, or fiberglass.
For more information on ways to detail vented cathedral ceilings, see How to Build an Insulated Cathedral Ceiling.
Creating a foam-free unvented cathedral ceiling is challenging. The only approach that I can think of is to install a thick layer of semi-rigid mineral wool insulation above the roof sheathing, followed by another layer of roof sheathing. The mineral wool insulation would need to be thick enough to keep the lower layer of roof sheathing above the dew point during the winter.
While it’s fairly common to install semi-rigid mineral wool insulation…