Posted By smartwall on 28 Sep 2015 08:09 AM
Eps is made from pentane, hardly green
EPS is
blown with pentane, not
made from pentane. EPS made of polystyrene created from feedstocks of ethlylene and benzene. and the density of roofing EPS is typically 1.5lb per cubic foot, and runs about R4.2/inch.
Pentane has a 100 year global warming potential about 7x that of CO2.
Sprayed polyurethane foam roofing is typically 3lb per cubic foot closed cell polyurethane created from feedstocks of polyols & isocyanates, blown with HFC245fa, and runs about R6.5/inch.
The HFC245fa blowing agent (almost universally used in North America) has a 100 year global warming potential about 1400x that of CO2.
The 3lb spray foam uses 27% more polymer per R and a blowing agent that is 2000% more damaging, so there's no question that EPS is a far greener type of insulation (and far cheaper ) type of insulation than 3lb polyurethane.
But is any foam green?
In situations like this it's not easy to design all foam out of the stackup, but opting for the lesser of evils is still a worthwhile consideration.
Polyisocyanurate is also blown with pentane, and is made from the same feedstocks as polyurethane. Typical roofing polyiso is 2lb density, and R5.5/inch, but has performance issues at very cold temps.