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.
I am finally underway with my project!
The insulation contractor has asked me about my desire to re-install the fiberglass over the spray foam on the concrete walls. He's concerned that the fiberglass will keep the inside edge of the spray foam cold which would could cause condensation at that interface. Is this a reasonable concern? I suspect that the concern may also be practical, since it's going to be a little difficult to compress the fiberglass back into what's left of the stud bays and put up the drywall without getting any of the fiberglass folded over a stud face. Doing research elsewhere (see "Flash and Batt" discussions at Green Building Advisor, amongst others) this looks like a reasonable concern but I thought I'd check here too.
He had no concern with doing this on the 2x6 wood walls, since those will have a vapor barrier.
Thanks in advance for your assistance.
Last edited by Schopsy; 01-11-2014 at 09:49 PM.
As long as the ratio of foam-R to fiber-R at the above grade sections is equal to or greater than the IRC 2012 prescriptive levels for exterior foam and using a closed cell foam, you're golden. 2x4 is presumed to have no more than R15, 2x6 no more than R23. So a ratio of 1/2 (R7.5-foam/R15 fiber) doesn't need OR WANT an interior side vapor retarder in US climate zone 6.
You're either on the warm edge of zone 7 or cool edge of zone 6. With 2" of R6/inch foam you're at R12, which is PLENTY of margin with a 2x4 wall on the interior side of it. With only 1" you'd be in tough shape for the 2x6 wall in zone 7, but just fine in zone 6.
Under no circumstances should you put an interior side poly vapor barrier (especially below grade) with a flash'n'batt approach! That will create a moisture trap and severely impede the drying rate of the assembly! If your foam/fiber ratio is too low per the IRC prescriptives, you can use a "smart vapor retarder such as Intello Plus or Certainteed MemBrain, but never polyethylene.