Apologies if this topic has already be addressed but I'm still scratching my head after searching the old posts.

We installed 9/16” x 5” engineered plank directly over main floor concrete using a full spread glue down (Sika T-21). The results were amazing (thanks largely to this site)-- Hard work, but beautiful and solid as a rock.

We’ve now moved to the second level of the house which has an OSB subfloor (7/8”, 16” on center). I’m fairly certain the subfloor was exposed to rain during construction but still looks to be in decent shape. We thought about adding an improved plywood underlayment but the current subfloor sets up for perfect transitions into adjacent rooms (bathrooms etc.) without moldings, so we want to avoid adding height to the floor for aesthetic reasons.

We installed a test area over the OSB using an insulayment layer and 1-1/2” staples. Almost immediately there was some squeaking and crackling when walking. This will eventually drive me crazy so I'm now considering a full spread glue-down directly to the OBS like we did on the first floor concete. The manufacturer said either stapling or glue down to OSB is fine, but I wonder what this board thinks. Pros/cons?

Thanks a lot!

Every installer may have hos own method that differs from everyonbe elses. But me, I hate OSB, it scares me and I don't trust it. You can usually tell if its been rained on and as it swells, it does not dry back down to the same consistancy as new. It looks all fluffed up, thats why it will not hold like new does. I have pictures that would convince anyone, but cant post them.

You dont want to glue directly to the actual subfloor, you need a need a new ply underlayment because when it needs repair or replacement what happens then? Plus your gluing to flakes.