I'll be installing Mohawk laminate flooring on second floor of 40 year old Townhouse. The existing subfloor has a little give, and I think the prescribed approach to stiffen an existing subfloor is to add additional plywood, screwed to subfloor, but not screwed to joists.
What is the minimal thickness I can use for this project? I'd like too add as little additional weight and height as possible while still achieving the goal of stiffening the floor a little to avoid stress on laminate planks from any vertical flexing of subfloor.
Is OSB acceptable? If so, what kind of screws should I use for OSB?
If the goal is to stiffen it I'd be using 1/2".
I also would not be screwing it.
Any place a screw goes in it will leave a dimple.
As the screw hits the bottom layer it's going to try and push the second layer up.
Take a whole lot longer and cost far more.
8 D ring shanks every 4" on the edges and 6 to 8" in the field will work fine.
Not a fan of using laminate on a second floor for several reasons.
It's loud to walk on.
Going to be a pain to transition where the stairs are without having a trip hazard.
This has been discussed many times on here before.
Engineered, or prefinished hardwood would be a better choice on this one.
That way you could use a normal landing tread at the head of the stairs so there was no expansion strip needed.