I recently did a remodel of a duplex into a single family home. This remodel included moving duct work and also relaying hardwood floors. The company we used to lay the hardwood did a very poor job filling in the old vent holes in the subfloor. The wood flooring is very thin and now it is bending when stepped on in certain areas, due to the fact that there is no actual subfloor underneath. I have patched subfloor from below before but the problem is some of these areas are no longer accessible from the basement. Is there any way to bolster the floor or fix this from the top down without having to rip up the floors and patch it. All attempts to get this remedied by the company have been fruitless, I’m considering it a lost cause.