How do you insulate floor of cabin built on piers that has exposed crawl space and also keep the mice out? I want to insulate floor from underneath cabin. Cabin is in northeast U.S. and subjected to winter weather.Floor Joists are 24" oc.


You fill the joist bays with fiberglass or mineral wool batts, then you cover the underside of the joists and batts with a few inches of rigid foam or rigid mineral wool boards, and then you protect that layer by covering it up with plywood or OSB. One layer has to be your air barrier. If you use rigid foam, make that your air barrier and caulk and tape the seams. If you use rigid mineral wool, the plywood will be your air barrier so caulk and tape the seams. I think mice would be hard pressed to chew through plywood from the bottom while crawling up piers, but if they can, protect the piers themselves with downward-facing anti-mouse cones made of metal or something.

  • Closed cell spray foam will also give you a moisture barrier as well. That could be used in place of the batts and rigid foam setup. – Jason Hutchinson Feb 11 '15 at 20:44
  • True, but it would be more expensive and provide less insulation if you only sprayed between the joists (which would leave thermal bridging) or make it awkward to apply the protective plywood (if you fully encapsulated all the joists with spray foam). It would also be more of a fire hazard and have worse environmental impact due to the not-so-green aerosols involved. – iLikeDirt Feb 11 '15 at 20:56
  • Also, you don't really want a moisture barrier on your floor in a case like this. If there's a spill that wets your wooden subfloor, and it can't drain due to a bunch of spray foam clinging to the underside of the subfloor, it's gonna rot that wood. – iLikeDirt Feb 11 '15 at 20:57
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    Thanks to iLikeDirt. Going w your suggestion. Will use Roxul 24" Mineral Wool Batts (fire proof),poly foam & OSB.I agree mousies would have a hard time.Thanks for your expertise. P.Pine – P. Pine Feb 12 '15 at 6:46
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    Roger,EPS it is. Im fortunate that I have 40" to work under cabin.Tks 4 clarification .Im good to go.P.Pine – P. Pine Feb 12 '15 at 19:28

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