jimmysisson
Veteran Member
- Joined
- Jul 11, 2005
- Messages
- 2,358
- Location
- W.Mass
- Tractor
- 1993 NH 2120 (the best), 1974 MF 135 (sold, but solid), 1947 Farmall A (bought, sold, bought back, sold again), 1956 MH50 lbt (sold, in 1980, darn it)
The new thinking on crawl spaces (in some parts of US) is NOT to vent them. Your profile doesn't say where you live, but humid summers/dry winters are widespread. I live in an area with high summer humidity, and you actually have a drier crawl if it's not vented. 6-mil poly laid on raked subsoil, joints taped, poly runs up the foundation and stapled to sills. Make it all tight, overdo it wherever you can. That keeps ground AND foundation dampness out of the framing. Code-wise here you need PT for anything within 8" of the ground (code ignores poly) and I'd be tempted to use it as you're describing. Not too big an upcharge to get the peace of mind of no rot.
We've built several buildings with the ply-foam-ply sandwich, my barn/shop/garage/woodshop/MIL apartment/woodshed/tractor shed is a good example. You can use cheap sheathing like OSB for the bottom layer, then iso foam (with the foil faces) and your good UL layer of ply for the "finish" floor. It's a bit tricky screwing down the final layer to hit the joists. Make sure all the joints are not aligned with each other (rip the first sheet of foam into quarters). 1/2" osb, then 2" foam, then 3/4" ply means a 4" screw is minimum. Use adhesive on the osb layer to help brace the joists.
Good luck, Jim
We've built several buildings with the ply-foam-ply sandwich, my barn/shop/garage/woodshop/MIL apartment/woodshed/tractor shed is a good example. You can use cheap sheathing like OSB for the bottom layer, then iso foam (with the foil faces) and your good UL layer of ply for the "finish" floor. It's a bit tricky screwing down the final layer to hit the joists. Make sure all the joints are not aligned with each other (rip the first sheet of foam into quarters). 1/2" osb, then 2" foam, then 3/4" ply means a 4" screw is minimum. Use adhesive on the osb layer to help brace the joists.
Good luck, Jim
