Heres a question, why are you removing the old floorboards and replacing them with the hardwood and not just laying the hardwood straight on top of the floor?
The old boards were in a bad way and where the walls have been removed the two floors are at different heights so no sensible way to go from one to another without lots of fiddly work.
Heres a question, why are you removing the old floorboards and replacing them with the hardwood and not just laying the hardwood straight on top of the floor?