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Benefits of stemwall insulation inside of a vented PNW crawlspace?

finePNW | Posted in General Questions on

My crawlspace is increasing by about 60% in terms of exterior perimeter wall. We have added insulation to the outside of the stemwall for a number of reasons, and now are looking toward the existing crawlspace for insulation ideas. The entire crawlspace will have minimal venting (~ 150 sqin of vent space for every 1500 sqft of crawl), 10 mil polyethylene battened to stem walls and with overlapping seams taped, but I cannot add exterior insulation to the majority of existing crawl stemwall due to setback restrictions.

The original idea was to insulate on the inside of the existing crawlspace to try to capture any heat the sneaks into the crawlspace from the floor joists and potentially pseudo-semi-condition the crawlspace (especially if I plug the vents in the winter).

I’m wondering if there would be any benefits to adding insulation to the remaining (existing) crawlspace stemwall or if it a) will make minimal difference in crawlspace temperature and moisture problems [even if I plug the vents in the winter?], b) might even be counter-productive in terms of releasing any heat that has built up in the stemwall from the upstairs framing directly to the outside without letting any into the crawlspace.

The existing foundation is also a little shallow and there is no damp-proofing on the existing crawlspace stem walls, so I’m wondering if faced rigid insulation on the interior of the existing stemwall might help some with either or both of those … or maybe it’d hurt because less heat would be made available to seep into the soil (and prevent frost under the footers) from the crawlspace air and drying to the inside would be prevented … then again, stemwall not drying to the interior is probably what I want, right? … I’m doing a bit of mental gymnastics here, and now am more confused then when I began!

Anyone have any thoughts on the subject? At the moment, an encapsulated crawlspace is off the table, unfortunately, but I’m plenty aware of the benefits at this point. Thanks!

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