Dana is a wealth of information on this stuff and I always enjoy reading his posts and those of really good applicators like dlarrivee.
Thanks for all the great responses!
Sorry to bring a dead thread back to life...
I've gotten several quotes for spray foam. They're all close in price. The one I'm leaning toward is proposing to use 2" of Demilec Heatlok Soy 200. Any thoughts on this product?
It's decent stuff. Don't put too much stock in the greenliness of "soy" business, since the soy fraction is but a fraction of only one of the two chemicals used (less than 15% of the total by weight.) Like any 2lb foam the competence & experience of the installer is the most important consideration for getting both good performance and zero problems.
Like most 2lb foams out there, Heatlok Soy 200 is blown with HFC245fa (Enovate® 3000 is a trade name for HFC245fa), which has a global warming potential (GWP) about 1000 x CO2. But in the past year or so HFC245fa replacement blowing agents have been commercially launched with GWP less than 10x CO2, notably Honeywell Solstice®, and Dupont FEA-1100 ®. When all else is pretty much equal, it is by far greener to go with the low GWP blowing agents. I'm not sure which foam vendors have picked it up at this point, but I expect HFC245fa to become banned for this use at some point, now that there are credible alternatives out ther.
Though not-so equal by R-value and vapor permeance, Icycnene has a water-blown 2lb foam (MD-R-200). It's about 3-4x more vapor permeable at any given thickness, and only ~R5/inch, but neither of those issues would be a problem in your application. At 2" you'd be at at ~R10 rather than ~R13 with the HeatLok Soy 200, but it's a far greener product due to the comparatively high GWP of the blowing agent.