Emerson has moved into a house in Climate Zone 4A, a region where humidity can be relatively high. As Emerson explains in a Q&A post, the crawlspace beneath part of the house has been closed to the outside, and now the question is how to insulate the space to help keep the house comfortable.
Emerson refers to an article on this topic posted by Carl Seville in 2011, and in particular to a comment from Ted Clifton who advocates the addition of insulation in the floor above the crawlspace as well as walls, and possibly the crawlspace floors. Clifton’s approach is aimed at keeping warm, humid air away from cold surfaces to prevent condensation and the moisture problems that would follow.
“I have read with interest Ted Clifton’s comments on closed crawlspaces in which he advocates insulating the walls and the floor (comment #9),” Emerson writes. “But I’m unclear on the recommended R-values for floors.”
Emerson has added a polyethylene vapor barrier over the concrete floor, and 2 inches of rigid foam insulation on the walls. In considering Clifton’s recommendations, Emerson is thinking of adding R-38 of batt insulation between the 2×10 floor joists above the crawlspace. Stone walls (R-3) on the first floor help make Emerson’s bedroom cold.
The crawlspace is adjacent to the conditioned and finished basement, connected by a 2-foot by 3-foot open grate. “The crawl is notably cooler than the basement, and our bedroom above is also chilly,” Emerson says. “So, we were thinking of double insulating, e.g. the crawl ceiling also, to keep heat in our bedroom. Note, there is a heat-pump water heater on the far side of the furnished basement. To our knowledge, no moisture issues in past many years, although we are new to the house.”