Foam insul between subf. & finish floor
BDohrn
| Posted in Construction Techniques on
I ahve an odd situation where I need to build up 3/4 inch above a subfloor and under a strip wood floor. Originally an above subfloor radiant tube sandwich was going in there, but it’s been eliminated in about 650 sq ft. The rest of the floor still has the tubes, so I need to meet that level. The whole floor is above an unisulated basemnt.
Thus my question: would it be nuts to kill two birds with one sheet and put foam insul — like polyiso above the plywood subfl and below the strip wood floor? (It would also soundproof to the basement).
Replies
Two reasons not to do this:
1. Foam board will compress over time and cause squeaks and/or cracked tongues.
2. Standard floor-nailer staples for ¾" hardwood strip flooring are 2" long. To drive through ¾"-thick foamboard at a 45º angle and find the solid subflooring, you'd need 3¼" nails or staples...and I don't think anyone makes them that long. I've never seen any.
If you need to bring up the floor ¾" so the levels match, use plywood, or Aspenite at the very least.
Dinosaur
How now, Mighty Sauron, that thou art not brought
low by this? For thine evil pales before that which
foolish men call Justice....
THanks. What do you think about sleepers something like 16" OC. Insul between?
That'll work.
To help avoid squeaks, lay the sleepers directly over the joists, screwed and glued. Glue them with PL Premium and screw down right through the subfloor into the joists with #8 flooring screws.
Oh, yeah, and do make sure the insulation panels don't sit proud of the sleepers....
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
Sleepers and foam board would be fine, but use XPS. It generally has a higher compressive strength than Iso and is more durable. Use minimum 25 psi.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
BDohrn
Building up with strips of 1 x 4 or something like it and foam between will, indeed, work, but it will also really slow down the installation because you won't be able to simply swing the nailer into any position at all and fasten.
You can omit the foam, too, although that would slow the installation down even more. It won't make any difference to the floor.
Myself, I'd lay down a sheet of OSB, fastened very thoroughly with staples or screws or ringshank nails. I wouldn't glue a sheet material with PL because the glue will not spread thin and there will be small hollows left between strips of glue.
Fastening the flooring to strips whether there is foam there or not will give it a hollow sound when you walk on it. If you fasten to solid, you know what that is going to sound like.
Ron