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Attic Insulation

The house uses raised-heel roof trusses to allow for 18″ of blown-in cellulose above the second floor ceiling. For maximum effectiveness, that insulation has to extend to the outside edge of the four-inches of R-Max foam board that will be attached to the exterior of the long sides of the house (the gable ends will be handled differently and discussed later). Regardless of what we used to contain the insulation at the outer edges, we knew that it would be easier to install before we installed the Zip sheathing on the second floor ceiling.

Our initially thought was to use insulation netting as a baffle to contain that insulation at those two outside edges. But after giving it some thought, and discussing it with an insulation sub, that idea didn’t seem ideal. We felt that the netting would be too unstructured; potentially allowing insulation to interfere with the soffit vents and the flow of air to the ridge vent. That same quality would also make it difficult to install properly, as it would have to drop down between each of the 2×4 truss members. So we settled on an alternative using OSB and some 2×6 blocking.

The OSB, ripped into two-foot-wide strips makes up the exterior baffle. The 2×6′s were stood on edge and placed between each of the 2×4 truss members to a) complete the baffle between the truss members and b) create a backer that the lower edge of the OSB baffle could be nailed to. The top edge of the OSB was then tacked into the truss members that formed the roof line. While it may be a bit difficult to picture after reading, it was fairly inexpensive and easy to execute. It took five sheets of OSB and ten 2×6′s.

Here are some photos that show the different elements and perspectives:

Here you can see the 2×6′s that were attached between the truss members, above the 2nd floor ceiling:

In this photo you can see the two-foot wide strips of OSB tacked in place to the 2×6′s (at the lower edge) and the roof members of the truss (at the upper edge):

The gap that you see between the 2×6′s and the ceiling in the photos above and below is 3.5″ wide. The bottom of that gap will be covered by the 4″ of foam board that will be attached to the outside wall. So, in effect, the top edge of the foam boards, which will run along the bottom edge of the truss members, will complete the floor for the attic insulation.