[masraum]

Originally Posted by gregpark

Good point Steve, but if you look closely, the heat duct sheet metal appears to be bent over the subfloor and under the first layer of flooring which leads me to believe the first layer of flooring is not T&G. Regardless, it's more than likely destroyed beyond repair. The nail you see is to pin the metal to the side of the opening to allow a heat register cover to drop in.

Got ya! I see that now. Seems like weirdly thin shiplap or heavily sanded TnG, but then it sounds like some wood flooring is thinner when new than I'd expect.