Dave Feldman is building a new house near Boston, Massachusetts, that will have a walkout basement with a tile floor. His goal is to have the floor comfortably warm in this Climate Zone 5 locale even in the dead of winter.
Feldman plans to insulate the basement walls with closed-cell spray polyurethane foam. For insulation below the slab, Feldman is considering two types of rigid foam insulation—expanded polystyrene (EPS) and extruded polystyrene (XPS)—as well as closed-cell spray polyurethane foam.
He’s uncertain whether to insulate the slab with 2 inches of foam (which he estimates at R-10 to R-14) or invest in 4 inches of foam and double the R-value.
“I don’t want to waste materials if there’s not a useful impact,” he writes in a post in the Q&A forum, “but [I] also don’t want to skimp on something that’s pretty much impossible to change once the house is up.”
His request for feedback is where we begin this Q&A Spotlight.
Please, skip the spray foam
The spray foam that Feldman has in mind is Demilec’s Heatlok HFO High Lift, which uses a hydrofluoro-olefin (HFO) blowing agent developed by Honeywell. HFOs have a much lower global warming potential than conventional blowing agents, but in Dana Dorsett’s view, spray foam is still a poor insulation choice.
“Why?” he asks. “That is some of the lousiest bang/buck going, and one of the least green methods of insulating a framed wall possible, despite using HFO blowing agents. Expensive (financially & environmentally) closed cell foam between framing is a waste.”
Dorsett directs Feldman to this article from Fine Homebuilding magazine explaining the basis for his conclusions while suggesting that dense-packed cellulose is the best choice for cavity insulation.
“Save the foam budget for…