Dense packing an eyebrow roof
I have a small eyebrow roof below a shed dormer on the back of my cape style house. The dormer runs for about 25 feet across the back of the house. The roof is attached to the wall studs instead of using the proper construction which calls for the wall to be sheathed first and then the eyebrow rafters attached to a ledger board across the sheathing. I have batt insulation in the wall that is exposed to the roof and to the soffit vents that are cut into the eave below the eyebrow. This roof/wall construction forms a very small triangular area that is a pretty big loser in terms of efficiency (air leaks, etc.). I want to close the soffit vents and dense pack the triangle. However, just like a typical kneewall, the joists below the dormer wall transition are wide open (no air blocking). My contractor thinks he can dense pack this area without putting some kind on insulbag/plug in each joist bay. This seems impossible to me. He can fill it with cellulose, but he can’t achieve a very high density without the cellulose simply travelling down the joist bays. Am I wrong here? Any good way to treat this area in a retrofit assuming we can’t cut/drill holes in the floor to install joist bay air blocking? Can a weatherization company typically get some kind of plug in place by going through the soffit?
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Michael,
It's hard to visualize the exact situation from your description, but it sounds like your analysis is correct. You need airtight blocking between each joist for this proposed solution to work.
When doing air sealing work, sometimes there is no alternative but to remove interior finishes (for example, part of a drywall ceiling) to gain access to areas that would be otherwise inaccessible. Fortunately, drywall is easy to patch.
Good luck.
Thanks Martin. I included a picture that describes the construction. I have the 'incorrect' (no sheathing) version of the construction. To clarify, the idea is to dense pack the quite small (you couldn't get a body into it) triangular space formed by the roof and the wall that you see in the picture. However, there is no blocking in the joist spaces below the wall. My weatherization contractor, who is doing a great job otherwise (work matches all great info I find on this site), suggested snaking the cellulose tube down the triangle from both of the kneewall attics that the 20-25 foot long triangular roof void terminates into on each end, but I don't see how we can get much density (air blocking) without getting an insulbag into the joist bay openings first. It seems that the access for the insulbag has to come from outside, either through the soffit area (mine is only 5 inches wide) or through the eyebrow roof. Access from the finished floor inside is prevented due to bathtubs and such up against the external wall. For what it is worth, I have read in several places that the kneewall sealing that I did on my 4 side attic space (I have a cape cod) will likely have little effect until I also find a way to plug this large leak. Once such source is the book 'Troubleshooting Guide to Residential Construction', which is the source for the picture attachment. Thanks again for any additional information that you might be able to add.