I'm installing a new hardwood floor as a diy home project and I've run across an issue I'm hoping to get help with on here.

The original subloor in the room I'm working in is 7/8" thick planks approx 3" wide. However, I've had to remove about 30sqft of it due to old termite/water damage, as well as to gain access to re-locate a radiator.

However, no one seems to sell 7/8" thick wood suitable for subflooring. Matching the thickness of the existing subfloor would, of course, be ideal.

I have already purchased 7/16" thick OSB which I intend to place down over-top of the subfloor and was considering doubling this up to match the height of the existing subloor in areas where original subloor was removed. In the end, the patched areas would consist of three layers of 7/16" OSB.

The joist are spaced 20" OC, and are also braced perpedicilarly every 24". My question is, will three layers of 7/16" thick OSB be sturdy enough for this situation. In my opinion, OSB is pretty flimsy in comparison to plywood, but at that thickness I think it would be fine.

Any feedback would be appreciated.

Thanks in advance

3 layers of OSB at the patch should be fine. But I actually would go with doubling up plywood for the patch,( just a couple sheets ), then sheet out with the OSB as planned.

Thanks for the advice, Howard. In that case I may use a sheet of 1/2" plywood along with a sheet of 3/8" plywood to get the thickness I need.

Is it safe to use pressure treated plywood for subflooring?

I always just use regular old CDX. Of coarse make sure to stagger the seams, and run sheets opposite direction to each other, or on a diagonal,( but more waste).

Pressure treated has far too much moisture in it to be used for sub flooring.

Thanks for all the feedback, folks. Much appreciated, and the floor is nicely patched up. Now I'm ready to throw down the last layer of subflooring which is a topping of 7/16th OSB.

So, I have another question:

Does it matter whether or not the edges of the subflooring are screwed into the joists, or is it ok just to drop it down willy nilly. It'll be glued as well.

My current plan is to go into the joists where I can, but not worry if the edges line up with the joist below since I'll be going into sturdy subflooring beneath anyway. Fewer cuts and less waste.

Can anyone tell me Best Practices as far as this concerned?

Again, thank you for all the feedback so far. You have all been extremely helpful and informative.

Thank you!

Sounds like a good plan to me. That 7/8" "sturdy" subfloor should be plenty to anchor into.

When you fasten a sheet...Start in the middle, and work your way to the edges. Also a good idea to leave approx. 1/8" gap at the seams, and expansion space around the perimeter of the rooms.

Thanks Howard, you (and everyone else who responded) have been a great source to go to. I'll definately be using this board if I run into any issues with future projects.