I have a split level townhome built in 1979. Due to moisture damage in a few areas (sliding glass door, kitchen, and shower surround) I need to replace some subflooring.

In the living room and bedrooms, there's 5/8" (I think)particle board on top of 1/2" plywood. In these areas, I plan to replace damaged areas only and in the end, will install some engineered hardwood and some carpet.

In the kitchen & bath, the existing subfloor consists of two layers of plywood - 5/8" (I think) on top of 1/2". In these areas, I'm replacing the 5/8" top layer (due to existing vynil that won't peel up) and any damaged areas of the bottom layer. In the end, these areas will have ceramic tile with radiant heat.

I know that current practice for tiled areas is to have 3/4" plywood subfloor with a 1/4" cement backer underlay.

My question is this... From a tile perspecive, Is 5/8" on top of 1/2" equal (or superior) to 3/4"? Obviously, the total thickness is more, but does the extra layer introduce any problems?

 

Your plywood is fine, what size are the joists and what length do they span?

 

.... and hopefully the plywood joints are staggered.

 

1/2" is unusual for a subfloor. Additionally, particle board (if thats what you really have) cannot be used anywhere in a ceramic tile installation, even if you cover it up with another layer of plywood. Partcle board swells to much with moisture changes creating vertical movement in the floor and will cause grout joints to crack and sometimes tile to crack as well. Are you sure you have particle board, and not OSB? Is the subfloor really only 1/2" thick, and not 5/8"?