Spray foam from crawlspace onto bottom of plank subfloor in Pacific NW?
Hi there – I’m in a 1955 house in Seattle, WA, over a vented, unconditioned crawlspace, with hardwood flooring on top of plank subfloor with no insulation under it.
I have read “Building an Unvented Crawl Space” and several related threads, and the advice to seal one’s crawlspace all seem to come with the caveat that in drier or Western climates the benefits are less. I even read the WSU study (http://www.energy.wsu.edu/documents/AHT_Conditioned%20crawl%20spaces%5B1%5D.pdf) that showed several sealed crawlspaces had higher winter energy consumption than vented ones, even when there was ductwork down there.
Given that I am starting from scratch, the easiest solution seems to be to have 2″ of closed cell sprayfoam sprayed directly onto my plank subfloor. It won’t nearly prevent thermal bridging from my 2×10 joists, but will be a perfect airseal and insulate a heck of a lot better than what I have.
The next easiest seems to be to install rigid foam boards against the bottoms of the joists and tape the seams. I’d also have to insulate the rim joists and I’d be sentencing myself to several weekends in the shallow (2-4′) crawlspace, but maybe the method is superior (and cheaper?) enough to justify the time.
Any advantages or disadvantages I might am missing? Is spraying foam against the bottom of plank subfloor a no-no for future repairability?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part