Retrofit Vapor Retarder/Barrier in Ceiling Plane
I finally crawled up into my attic of the house I purchased four months ago. I knew that I needed to add significant insulation (currently has about 6″-8” of loose cellulose) as I want to get to R60. In advance of adding the additional insulation I am air sealing the attic. I was digging around in the insulation to find the various wiring penetrations, to foam them closed, and I was immediately struck that I didn’t find poly (or any other vapor inhibitor) on top of the ceiling drywall, as is the typical scenario in homes in my area. The ceilings are textured with sprayed drywall compound, and are original to the home (house was built in 1980) so I am confident that the drywall ceiling does not have paint that can act as a vapor retarder. The attic is vented at the soffit and at the ridge, and there doesn’t appear to be any signs of mold or moisture damage on the underside of the roof sheathing. I haven’t been up in the attic during the colder months to see how much, if any, condensation there is on the underside of the roof deck.
Given that I have no vapor retarder, and I wish to keep a vented attic, I need to add a vapor retarder/barrier to the ceiling plane (Right?). The first and easiest way that immediately comes to my mind is to remove the cellulose and flash fill the truss bays with ccSPF at the ceiling plane, as it would accomplish both air sealing and installation of a vapor retarder/barrier in one shot. I would then fill over with blown in cellulose to the necessary thickness. Another idea I have would be to cut and foam-in board insulation, but that would be very arduous as the attic has limited room to maneuver the boards without cutting them into 3’ pieces, and I have about 1000 sf to do this to. What other suggestions are there for retrofitting a vapor retarder/barrier into the ceiling assembly?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part