The plan on our project was to use our 5/8" t+g osb as the air+vapour retarder. it has acoustic sealant on all panel edges and where it touches all framing members. the bc building code does not explicitly state panels can be used as the vapour retarder but it does allow for vapour retarding paint. that said, the inspector reallllllly doesn't like the idea of not using poly. the ceiling has an uninsulated 2x8 service core with the t+g on the exterior side. we plan to insulate to about r80 with fibreglass or cellulose.
Can I lay down some 6-mil poly on the exterior side of the OSB to appease the inspector so he won't give me any grief about using the vapour retarding paint everywhere else? (i.e. the poly would lay flat on the OSB between and in direct contact with both the OSB and the attic insulation...