Rotted bathroom subfloor replacement

2 years ago

I am in the process of replacing my rotted bathroom subfloor. The issue was so extensive that the problem affected the material under the walls and into the adjoining rooms. I’ve already reinforced with blocking between the floor joists and replaced the entire affected area with 1/2” ply. Glued and screwed to joists. The floor section in the adjacent bedroom as well as under the wall plate needs to have 1/2”. But I really want a 3/4” subfloor in the bathroom. Can I just laminate (glue and screw) a 1/4” ply on top for extra strength, staggering the seams? If I go any thicker than that, the transition between the two rooms won’t be the same. If I can do this, do I screw the upper layer to joists or just to the bottom layer?

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Comments (6)

millworkman
2 years ago
You can use the 1/4" staggered and I would screw only into the subfloor, not the joists.
D Brewski
Original Author
2 years ago
What about glue? I’ve heard people recommend both with and without.
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millworkman
2 years ago
You can absolutely thru some subfloor adhesive (PL400, Premium or the like).
klem1
2 years ago
Given a choice I'd much prefer 3/4 material instead of 1/2+1/4
D Brewski
Original Author
2 years ago
3/4” was not an option due to the subfloor ply I laid down is one piece and continues under wall plate and into bedroom for added strength Bedroom floors have solid hardwood floors over the original 1/2” subfloor so a 3/4” ply replacement wouldn’t have worked here either.
3onthetree
2 years ago
I'm not so sure if the 1/2" subfloor is as you say. Even if the house was old with planking, it would be 3/4" thick. My own house has 1/2" (for a specific regional reason) but was layered with another 1/2" from the get-go. 1/2" plywood alone needs sandwiched for a thicker floor to limit deflection (=sag), especially (no, critically) if you have tile in a bathroom.

Also not sure how you get subfloor under existing wall bottom plates. Either way you need to sandwich 1/2" by screwing layers to the joists, so you're essentially making up your own "plies" to be stronger just like plywood is made at the factory.