Insulating and protecting exposed floor joists
Good day
Due to proximity to a septic field, a corner of the project I’m working on is supported by a pier. The remainder of the house has a full basement under it. There is a 6′ x 6′ section of floor joist hanging out in the breeze, which is getting chilly here on Cape Cod.
My questions are:
1-What is the typical insulation for this setup? I’m thinking about cutting rigid poly-iso foam and then gun foaming it in tight.
2-What is the best way to seal the floor structure in after insulating? Seems like either PT plywood or cementboard might work.
Thanks
Chris
Replies
There is no typical on this
In the first place, most areas will not allow you to build any living space out over or within ten feet of a septic system, regardless of whether it is a pier or a full cellar.
A reason is to prevent methjane from entering the dwelling. So whatever you do, make sure to seal it tight
By cutting the foam, it sounds like you would place it between the joists. I think buildingscience.com detailed the best was was to attach the rigid foam to the underside and tape the seams. You could add fiberglass their too, but the foam will make the biggest difference.
followup
Thanks for the comments
The local code requires no foundation within 20' of the edge of the leaching pit. The closest corner (on the pier) works out to be about 15ft from the edge of the pit in this case.
Any thoughts re: plywood vs cement board/hardi-plank?
Thanks,
Chris
Disregarding the septic situation, I have done a few of these
using FG batts in the spaces, then foam spanning across the face of the joists, then plywood screwed up through the foam.
If you have room to lie on your back to do the work, it has enough clearance that rot and vermin should be no problem