The contractor insist that a plywood layer is not suitable for my
case. He said when he does new constructions he uses 3/4" plywood
because the sub-floor is not as strong as older homes so the plywood
is needed for structural needs. The wood subfloor you see in the
pictures are pretty thick and these types of homes don't need a layer
of plywood (mine was built in 1960). On the adjacent rooms where there
was hardwood floor, the hardwood sits directly on top of the subfloor,
there were no plywood in between... but hardwood is probably
differentn from hardyboard and can flex somewhat.

ah crap.

Raymond

How thick is the subfloor in your picture? Most subfloors are 3/4".
Hardwood flooring is usually put right on top of the subfloor, there
is no plywood underneath.