If that air gap (between the vapor barrier layers) is open to the outside world, then that construction should be OK, quite normal actually.camaro1969 said:so it will be 2 layers vapor barrier in the roof... with an air gap under the upper layer...
I'm confident in this construction at least
But any moisture between the layers should be able to vent/diffuse out somewhere.
Yes indeed, so we thought with the ventilation...
when the upper layer became diffusion-tight by mistake, we compensate with an additional lower layer of diffusion-tight plastic, so the moisture doesn't get into the insulation...
when the upper layer became diffusion-tight by mistake, we compensate with an additional lower layer of diffusion-tight plastic, so the moisture doesn't get into the insulation...