Crawl space: open-cell spray foam?
We are planning on encapsulating the crawl space in a house on the border of zones 4 and 5 in NJ. It’s been vented for 58 years but it’s time to fix that. The plan is to close the vents, put polyethylene on the dirt floor, and insulate the foundation walls. The question is what to use for insulation. We are lucky to have a highly recommended contractor who is fluent in building science and home performance. He recommends open-cell spray foam for the foundation wall and the rim joist area. I’m nervous about open-cell for the below-grade portion and would be more inclined to use EPS for at least some of that. I’d like to get your opinions on whether open cell would actually be fine, or whether it’s important to use EPS or similar for the lower section.
It a CMU block foundation wall, about 3.5 feet from the dirt floor to the joists. About 3 feet of that is below grade and about 6″ above. Last summer’s torrential rains resulted in some water coming in the vents and collecting inside, but that’s being fixed with some re-grading and by closing off the vents.
There’s no capillary break on the top of the block wall, so the motivation for the open-cell foam is to allow the CMU to dry inward and avoid having water wick up and keep the sill plate wet. The following BSC information sheet recommends EPS or open-cell foam inside crawl spaces as two options that allow drying to the inside.
But their drawing shows a crawl space with the dir floor level above grade, vs. this house which has most of the crawl space below grade. So it seems that opting for the lower-permeability EPS could be safer than the higher permeability open cell foam–I worry that it would become saturated with moisture, both from moisture wicking in through the concrete from the soil, and moisture from the interior air condensing against the cold concrete near the bottom of the wall.
Which of these options are acceptable and which is best?
1. EPS for the whole foundation wall and OCSF for the rim joist area.
2. EPS for the bottom two feet of the foundation wall and OCSF above that.
3. OCSF only.
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