Crawlspace insulation in a humid environment
Hello All,
As the subject implies, I’m wondering about the best way to insulate a crawlspace here in coastal Virginia. Our code requires R19 insulation in the joist bays but, everyone I speak with here thinks this is a recipe for mold, rot, etc. (even though they do it to meet code) Especially when large multiple flood vents are required.
An alternative that’s often presented is locally referred to as encapsulation. This is where I’d air seal and insulate the perimeter of the crawler, cover all with 6mil poly and install a de-humidifier. This seems even more problematic to me, unless we also add conditioned air and if the de-humidifier were to fail for any length of time, unknown to us.
I’ve read a few articles published in FHB about this situation one of which seems reasonable ie; insulating joist cavities then covering with 1-2″ of rigid poly is0 and taping/sealing the seams. But again, with all I’ve read about letting building envelopes “breathe” I wonder if this (rigid layer) would create issues as well.
First, if we do either option, I’m a big fan of mineral wool insulation (from my commercial construction background) and would use this as much as possible.
Second, and this is my actual question: I wonder about covering the bottom of the joists with a WRB (Tyvec, etc.)? Either attached to the joists themselves, or to 1x strapping to create some separation between the WRB and the insulation. It seems to me this might allow the assembly to “breathe” more and be an efficient/effective solution.
Am I all wet???
Any thoughts would be helpful (I hope).
Replies
Personal experience in muggy TN. We bought a condo five years ago with ventilated damp crawlspace, condensation dripping from pipes and musty odor, and moldy fiberglass bats draping from the joists.
Quoted about $10,000 to encapsulate, but did it myself, sealing vents, 2" rigid foam on foundation walls, plastic floor liner and dehumidifier hung from joists with condensate pump for less than $2500. Set the dehumidifier to 55% to prevent mold growth. It ran for several days non-stop, but only rarely thereafter. No insulation needed between the joists. Don't think there would be any need for WRB if the encapsulation is done.
Not an expert, just a DIYer.
Thanks. Good info. Glad to hear it works. What was the cost of the de-humidifier?