We are finishing out the space next to the garage in an existing home. Living space is currently on second level. We are installing a floating floor over concrete slab. We have 2 layers of 1″ XPS both layers taped with 3/4″ T&G Advantech plywood on top. We were told not to screw through into the slab by our friends at BSC because they have seen many warped floors that have screws. We stopped the ply 3/4″ from walls. We have not installed the oak floor yet and we have lots of squeaking (sounds like the XPS is rubbing against itself) when we walk on the plywood. Has anyone had this problem? Will the 3/4″ oak provide enough stability to eliminate the problem? We filled the gaps at the exterior wall with spray foam for a continuous thermal barrier.

Thanks for your thoughts,
pam