In June 2010, Alex Wilson published a ground-breaking article, “Avoiding the Global Warming Impact of Insulation,” in Environmental Building News. In the article, Wilson examined the implications of the fact that the HFC blowing agents used to make extruded polystyrene (XPS) and most types of closed-cell spray polyurethane foam have a much greater global warming impact than CO2. As it turns out, the negative global warming impacts of escaped blowing agents from some types of foam insulation can sometimes outweigh the positive climate impacts attributable to energy savings.
Needless to say, the article generated a great deal of discussion. (A shorter version of Wilson’s article appeared as a blog on GBA.) As a direct result of this article, XPS became the pariah of the rigid-foam world — at least for green builders. (The problem of HFC blowing agents should not be confused with questions surrounding the flame retardant HBCD, another problematic component of some types of foam insulation. Because both XPS and EPS contain HBCD, the “greenest” type of rigid foam is polyisocyanurate.)
Insulation materials can affect our climate in at least three ways: one positive way and two negative ways.
When you calculate the embodied energy of an insulation material combined with the effects on the atmosphere of escaped blowing agents, you can determine the “embodied global warming potential” of an insulation.
There are many reasons to install thick insulation on your house: to improve comfort for the occupant, to reduce energy costs, and to lower your contribution to global warming.
According to Wilson’s article, it’s possible to install “too much” XPS on your walls — that is, too much from a perspective of global warming. Of course, even if you install “too much” XPS, the extra insulation will still help keep you comfortable, and it will still help lower…