Condensation and Vapor Barrier with Rockwool Insulation in Roof
I waited a couple months to put up the poly Iso and now the rockwool is wet, is this a big deal?
My roof assembly is =
-Asphalt – Graces – Advantech roof sheathing. Roof is a 6/12
-Rafters are 2X12’s with 1.5″ air vent from soffit to ridge created with 1.5″ EXP spray-foamed in. Then 8″ rockwool and strapping to hold it in.
I got to this point in the fall and stopped to work on the siding. Now I am back inside and finishing the ceiling. When I removed a piece of the rockwool I found condensation, which makes sense.. I think. All the vapor in the air is going through the Rockwool and condensing on the colder EXP. So I took all the rockwool out and setup fans so it will dry.
My plan now is to let it dry out, put the rockwool back in and add a layer of 2″ poly Iso taped at the seams and edges. My theory is that once the ceiling cavity is air tight from the inside, no vapor can get in and no more condensation. After the 2″ of Poly, I will strap with 2X4’s and then sheetrock.
Does this roof assembly make sense? Thanks for your input!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part