…if you care about climate change.
Building insulation reduces greenhouse gas (GHG) emissions associated with space heating and therefore has long been a strategy in climate change mitigation. Unity College students learn about life cycle analysis in their Environmental Sustainability course so they and other environmentally-literate citizens know that there is some GHG cost in the production and eventual disposal of insulation that will subtract from these savings.
As it turns out, the GHG emissions from insulation are much higher for some forms of insulation than most of us have probably assumed, and the differences in global warming potential (GWP) for different insulation choices is huge. Environmental Building News (June 2010, Volume 19, No. 6) documents the findings of several researchers on this issue.
The foundation insulation and the SIPs panels of TerraHaus will use variations on one common form of insulation known as expanded polystyrene (EPS), also known as “beadboard.” EPS was chosen because the typical GHG “payback period” (the fuel oil energy savings needed to offset its manufacture) is about 4 years for R-50, the insulation value of the TerraHaus walls. Compare this to other common forms of insulation:
EPS (beadboard) 4 years
XPS (such as Corning Pink Board*) 98 years
ccSPF (Closed cell spray foam) 80 years
Cellulose ¼ years
Polyisocyanurate (Tuff R or Celotex; foil backed) 3.5 years
*I wrote to Dow about their blue board which historically has had the same payback as Corning’s pink board. I got a detailed and clear answer about the new ozone-friendly blowing agent that they have switched to using, but the answer with regard to the GWP of its blowing agent was much less transparent. I’m still not sure where their product stands. Yes, the energy used in manufacturing the product is quickly paid back in space heating savings, but what about the potency of the blowing agent as a GHG?
These estimates were modeled for Boston. In warmer climates, the payback will obviously be longer.
The problem with XPS and closed cell spray foam (high density spray foam) is in the blowing agents used to expand the products to size. These blowing agents are gases with many times (1000 to 1500 times) the potency of carbon dioxide as greenhouse gases. The estimates used in the studies assume that 50% of the blowing agents will escape over time. Others feel that this estimate is too conservative.
Should we avoid closed cell spray foam completely? Note that the above analysis looks only at the conductive heat loss values. In other places in this blog I have emphasized that both insulation for conductive losses and air sealing for convective losses are important. The GWP in this analysis is probably too hard on spray foam, as spray foam can be used effectively for air sealing; if air sealing was taken into account, spray foam should pay back in less than 80 years. Also, the whole insulation and sealing system should be analyzed because combinations of insulation choices are often used. Spray foam for air sealing should be used in combination with a blower door to find invisible missed spots because spray foam doesn’t air seal quite as well as its users usually assume.
One lesson from this article: if you are concerned about climate change, make sure your architect and builder are green building experts who follow journals such as Building and Environment, Environmental Building News, and Building Science.
Foundation: R=32 8″ EPS @ R4/inch
Wall: R= 55 3.5″ BIB@ R4.3/inch; 8.25 EPS SIPs @ R 4.8/inch
Roof R=84 24″ DPS@ R3.7/inch
Doug Fox, Director, Center for Sustainability and Global Change, Unity College