OK a question or two for the group! Todays inspection (Beazer home) had a few issues with the flooring in the home. The joist system is a truss design that is 24"OC. It is covered with Norbord OSB that is 23/32" or 18.2mm thick with a Type 1 and PS2 rating. On top of the OSB, Bruce wood flooring has been glued on to it. The flooring has pulled away from the OSB in many areas around the home. From what I can tell Bruce does not require an underlayment. APA (folks who rate the OSB) do not require an underlayment. Norbord, the manufacturer does not require an underlayment for the wood floor to be glued onto. But, they all have a caveat in their guidelines that all floor systems are different and steps might need to be take to stiffen the floor, such as underlayment. The floor seems to flex in a few areas, but not all over. It looks like this has been part of the cause of the flooring losing its adhesion to the OSB. Has anyone ever seen something like this? I have seen glue down wood floors on slabs act like this but never one on a conventional foundation. I always see an underlayment of around 3/8" on OSB floors when they installed wood floors either glue down or nailed.