I have built many floors with TGI’s, but never lived in one until now. My joist are way under spanned, and I have the problem I describe below with even the shortest span. 3/4″ subfloor, with hardie underlayment set in thinset 100% per specs, and then porcelain tile over most of the floor. I get a definite vibration in areas such as the kitchen sink, or bath where things can rattle. There is no grout cracking. At first I thought that the OSB was flexing a bit, my first OSB floor, so I put some blocking in one area between joist and that made no difference.

I remember reading that because the truss joist are so light that they cannot absorb vibration. Is this my problem? I am thinking of spraying the underside with foam insulation but don’t want to if that will not solve the problem. It’s just annoying, not critical. Nothing like a callback on your own house.

Any other solutions or problems I may have overlooked?

Thanks, John