Insulation for crawlspace – foundation and exterior wall
I’m in climate zone 4A. We have a crawlspace that (through work done by us and the previous owners) is no longer vented, has a vapor barrier, and has a dehumidifier. It used to have fiberglass insulation in the subflooring, but that was removed due to mouse infestation.
I’m looking to replace the insulation ourselves and from what I gather, now that we are more fully encapsulated and do not want more mice nesting (it was a serious problem), we should use rigid foam board on the walls of the crawl space.
My issue lies in not finding the advice that fits our needs (HOW to insulate is not the problem, rather WHAT to insulate). Our crawlspace has walls that are about 1/2 cinder block foundation and 1/2 exterior walls.
Can anyone point me to advice or advise me whether the following is the best approach to insulate these walls? I would attach/anchor foam to the cinder block (of the appropriate R value and allowing for a 3 inch termite gap), and then attaching foam panels to the exterior walls between the studs (filling in gaps with spray). But is that it?
Is this generally the correct approach?
Apologies if I am not using the correct terminology.
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Replies
You will likely need something rated to be left exposed, or will need to cover it with a suitable covering (1/2" drywall, 1/4" hardboard, etc.). In my case, I used a fire retardant additive in white primer, which satisfied the local requirement. I would use polyiso here, Dow Thermax (or Johns Manville's equivalent produce, CI Max) on the walls if you need the fire rating. If you don't need the fire rating, I'd use reclaimed polyiso if you can find it. I used fiber faced stuff, which worked great with the fire retardant primer, aside from sucking up a LOT more primer than I was expecting.
I like to attach the polyiso to the block using tap-in anchors such as the Plasti-Grip anchors. These are easy to use, just drill all the way through the foam and into the block, then insert the anchor and give it a whack with a mallet to set it. Easy and quick. Be sure to use enough to keep the foam panels flat against the wall.
For that above-grade portion, what's on the exterior? If it's basically just a mini version of a regular studwall, you could insulate it similarly using batts (I'd use mineral wool here for ease of installation), but you'd need an interior side vapor retarder. You could also use rigid foam IF the exterior will allow for drying. What you want to avoid is a double vapor barrier situation that would cause moisture issues within the wall.
Bill
Thanks for the reply. I would describe it as a "mini version of a regular studwall". It's a standard exterior wall that has vinyl siding.
I'm concerned about mineral wool batts because of how much of a cost, hassle, and nuisance the mice were even with continuous, professional pest control. They simply started nesting in the batts up against the wood frames. The smell was awful and required another company to come and scrub/disinfect it. So I'm trying to avoid that if possible.
I understand the need to ensure that we don't trap moisture, but I'm unsure how to determine if using rigid foam would allow for drying.
I would probably do cut'n'cobble foam here then. I normally wouldn't recommend insulating that way due to how much labor is involved, but it's probably the easiest way to avoid using batts and not having the foam over the studs where you have to deal with more obstructions.
I do recommend trying to seal out the vermin though. Mice can chew through foam too, they just tend not to build nests in it.
Bill