I am getting ready to install 3/4” x 5” prefinished oak flooring.
It is hardwood, not engineered.
This will be installed on the first floor above the basement, on top of existing subfloor.
Project is located in Western Pennsylvania.

I initially planned to just use red rosin paper and cleat nails every 8”, but upon more research it appears glueing is suggested for anything 5” or greater.

I really do not want the floor to cup, and if I have to spend some more money on glue then I feel it’s worth it. But is it really necessary?

If so, what type of glue is recommended? Is Loctite’s PL adhesives acceptable? Will that allow enough flexibility for movement?

Any advise would be much appreciated.

Thank you

If you don't want it to cup just make sure the basement maintains similar relative humidity as the the area above it. This is why a large majority of wider solid hardwoods fail. Higher moisture levels from below will find a way into the new floor eventually. Result? Expansion and cupping.