Flash and batt on a sloped roof
The spray foam crew started work on my house today. One of areas getting CC spray foam is the sloped portion of the roof on the room over the garage. For the sloped portion of the roof, there is roof sheathing, a ventilation baffle, spray foam, and the rest of the cavity will be filled with fiberglass batts.
Before doing the spray foam, the crew stuffed a piece of fiberglass between the rafters in the area directly above the kneewall. I asked about it and they said they basically use it as a backer at the top of the kneewall, so when they spray down the rafter they continue to spray down onto the piece of fiberglass.
I was skeptical of it at first, but thinking about it, I guess it makes sense. Is this a normal and acceptable practice?
Thanks.
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Replies
Michael,
The stuffed-batt trick will work, but it's probably not quite as good as using rectangles of rigid foam (sealed into place at the perimeter of each rectangle) for this purpose.
The hope is that you get a good air continuous air barrier. You kneewall may have an air barrier -- or the sloped roof assembly may represent your thermal boundary, all the way down the slope to your eaves.
If you have a convoluted thermal boundary that follows your kneewall, then you have to check if your air barrier is continuous. If the spray foam is the air barrier for the sloped section of your roof, then you want your spray foam contractor to connect the spray foam layer with the air barrier on your kneewall (which may be the drywall, or may be the rigid foam on the exterior side of the kneewall).