Before the first winter, we had a contractor blow the sidewalls full of insulation. While he was doing the job, he remarked that the walls were taking more insulation than he thought they would. We didn’t think much of it at the time, but this fall, when I was doing some other exterior work on the house, I had a chance to remove one of the 3 inch x 12 inch soffit vents and happened to glance up inside the eave box. The eave had a lot of cellulose fiber insulation scattered around, and by playing a flashlight up against the top of the exterior wall inside the eave, I could see why.
The carpenters who had built our house had omitted the last exterior sheathing board at the top of the exterior walls. This left an opening at the top of the stud cavities. When the insulator blew insulation into the sidewalls, the insulation went right out the top and into the eaves, leaving a section of completely uninsulated (and wide open, unsheathed) stud cavity around the upper perimeter of the house. By sticking a point-and-shoot camera up into the soffit vent opening, I was able to get some photos, and also to ascertain that the opening looks to be about 6 to 8 inches high.
For the last several years, I’ve been noticing that we get a few small ice dams on the roof in the area where the photos were taken. This was quite puzzling, especially since I had taken great pains to completely air seal the attic, added soffit venting and vent channels, and blown in 20 inches of cellulose fiber insulation on the attic floor. But heat has evidently been escaping through the back side of the plaster walls (the plaster keys of which are visible in the photos), and apparently melting the snow on the roof in this location.
The problem is what to do about it. The soffit material is carsiding, and because it is a tall, two-story home, removing the soffit in order to deal with the empty stud spaces would require erecting scaffolding—and a lot of messy, disruptive work. It’ll have to wait for this year, at least. Snow has already fallen where we live in Kalamazoo, Michigan, so it looks as though we’re going to have to live with it for the time being.
In the spring, though, I might just take on this challenge. I’ll probably fill the empty spaces with fiberglass, then fasten rigid foam board to the studs, and seal everything up as well as possible with spray foam and caulk. And then button up the soffit again with new carsiding—quite a lot of work. But just the thought of this empty stud space in our otherwise very energy-efficient house gives me the chills.
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