Attach Drywall through plywood

HooKooDooKu

I recently stiffened my floor joists in a bouncy upstairs room. Now I want to hang drywall from these floor joists for finishing in the basement downstairs.

When I stiffened the joists, I sistered some of the 2x8 joists with 2x10s. The other joists, I stiffened by attaching 2x4s laid flat to the bottom of the joist (to create something like an I-beam... or up-side-down T beam).

The result is that the bottom of the 2x10s hang below the level of the 2x4s by about 1/2". To get the joists "level" I want to rip some 1/2" plywood and attach it to the underside of the 2x4s.

Now the 2x4s have been attached in such a maner that they will be able to support the load of the drywall (they were attached with a combination of liquid nails, 3" long wood screws, and 3" nails). So from a support stand point, I want the drywall to be supported by the 2x4s rather than the plywood.

My plan is to loosely attach the plywood (perhaps just a few finishing nails to hold them in place) and then attach 5/8" drywall with 2" drywall screws.

Anything wrong with this plan? Any issues with plywood as a backer to the drywall?

tpolk

I would nail ply secure no reason to not and more solid b more better imo

HooKooDooKu

Well, now when I say "loosely", the idea would be that the plywood would not be mounted in a "structual" way (i.e. not designed to hold a load).

It would be sound against the bottom of the joists, but the only thing holding it in place (until drywall screws go through it) would be 1.5" long finishing nails. But since the nails would all be vertically oriented, if you attempted to pull DOWN on the plywood, it (or those finishing nails) would likely slide right off.

The idea is that the 2x4 studs firmly attached to the joists would be the support structure. The plywood is just a spacer.