Vapor barrier placement under bedroom floor

[JRobert Oppenheimer]

My sister and her husband are renovating our old home (she's the youngest so she gets the perks you know that lol). Anyway, for reference there's a garage below two heated bedrooms. The contractor wants to put the vapor barrier directly under the subfloor, then Rockwool between joists, and plywood last. I always thought the vapor barrier went after insulation, not before. Is this correct for this kind of setup?

 

[WrapAndTrap]

The vapor barrier usually gets placed on the warm side, just underneath the subfloor, with insulation underneath that. This setup prevents warm, humid air from getting into the cooler joist area.

We did the same thing at my cousin's house above a garage, and we haven't had any moisture problems since then. Is your contractor making sure the seams are sealed tightly? That's really crucial, too.

 

[Dayanara]

The vapor barrier usually gets placed on the warm side, just underneath the subfloor, with insulation underneath that. This setup prevents warm, humid air from getting into the cooler joist area.

We did the same thing at my cousin's house above a garage, and we haven't had any moisture problems since then. Is your contractor making sure the seams are sealed tightly? That's really crucial, too.

This is right, for a garage below heated bedrooms, putting the vapor barrier under the subfloor before the insulation is actually pretty standard. Trust your contractor

 

[birds.of.a.feather]

I'd say vapor barrier placement depends on climate, generally it goes on the warm side of the insulation. If the garage is unheated and the bedrooms are heated above, the warm side is right under the subfloor, so what the contractor suggested makes sense. Rockwool between joists and then the plywood sheathing will work fine