Dense-pack retrofit cellulose insulation for basement walls?
I recently had an energy audit done existing 1958-built tri-level in climate zone 5 (Ann Arbor MI). Looking for advice from the GBA experts to sanity-check some of the recommendations before making decisions; I’ll try to keep it to one question per post. One recommendation was to add dense-pack cellulose into the existing above-grade and below-grade (finished) walls. I see from the How to Insulate a Basement Wall article that cellulose and other air-permeable insulation materials are never recommended against the basement concrete wall.
Are there reasonable options between leaving the uninsulated below-grade walls as-is, and fully demolishing to the concrete and adding rigid insulation then rebuilding the stud walls?
Current state of the basement is fully-finished, with walls of .75″ drywall, 3.5″ studs with no insulation, fiber board (asphalted?). Not sure from there to the outside because I wasn’t ready to cut through that fiber board to inspect further – maybe an airgap or not, then poured foundation wall. The auditor estimated R9 but that seems optimistic. Above-grade exterior is brick veneer and that extends below grade a bit. No under-slab insulation. Moisture situation is good (overhang, gutters) but grading on one side is not ideal. Thanks for recommendations.
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It would be helpful to know if there is space behind the fiberboard; whether its against the concrete or if there is a gap that could perhaps be filled.
Phil,
Determining the risk of installing cellulose insulation in this situation is hard.
Obviously, cellulose isn't a great choice here, and you would only consider its use to save the hassle and expense of the right solution (which is ripping out the drywall).
The low-risk situation would be if (a) your house has a functioning footing drain and good exterior dampproofing or waterproofing details, (b) your basement has no history of water entry, and (c) the fiberboard you're talking about is asphalt-impregnated fiberboard.
Under those circumstances, the risk is low.
If, on the other hand, (a) The footing drain is partially clogged, (b) The surrounding soil is damp, especially after a heavy rain in April, (c) The basement has had a few water-entry events, and (d) The fiberboard isn't asphalt-impregnated, then you'd be nuts to install cellulose.
Thanks Bob for the follow-up, and Martin for helping me avoid a mistake. I'll put basement insulation wall at the bottom of the list of possibilities, only to worked if we end up with enough budget to take the drywall down.