Poly under subfloor

7/1/2017 at 1:10:09 PM

From my experience putting poly over the joist causes the joist to rot. You actually need to put the Polly on the ground or spray foam the entire cavity.

Use p/t lumber if it's exterior.

7/1/2017 at 1:11:58 PM

And what I mean about spray foam the cavity, means between the joist. Not the cavity all the way to the ground.

Hope this was helpful

7/2/2017 at 11:59:10 AM

Yes, on top, if your floor system is framed and insulated as the walls are.You would really be treating as exterior wall. So, insure that the underside of joist is sheathed and as air tight as is possible, just like you would do with any other part of the exterior of your home.

Regards