Air sealing attic – how do I address tight roof corners?
baltik
| Posted in General Questions on
Just had some original 1967 vintage r15 mineral wool batts pulled from my attic and will attempt to do my own air sealing. I have a shallow pitched roof so the perimeter is extremely difficult to access. Are the top plates of exterior walls a significant source of air leaks? If so what’s the best product/approach to get spray foam in those corners?
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Replies
Would love some advice
baltik,
Yes unfortunately the top plates are often a source of air-leakage, especially in houses without an interior air-barrier. The absence of responses to your question probably stems for the lack of easy options, and I'm not sure my suggestions will be that useful. Because the plates are interrupted by the rafters and trusses that bear on them, and that the air often comes from between the sheathing and plate, it's hard to effectively use sealant or membranes.
Spray foam is difficult to contain without some backing, which as you say is very hard to install in low pitched roofs. All I can suggest would be to try a bay or two with liquid flashing, and see how well you can seal the cracks and voids. It won't be a pleasant job. Good luck!
Given the limited access I don’t think the juice is worth the squeeze.
Yes, I would make the effort in the few bays with holes in the top plat for wires and pipe.
I would focus my efforts at making the interior surface of your drywall as the air barrier. Tape a box fan into a window or two and use smoke from incense sticks to locate the leaks and add caulking behind the trim and around the electrical boxes. Where you stop the flow is irrelevant so long as the flow stops. Yes you will have a lot more liner feet to work on but at least there are no nails to bang your head into.
Walta
Hi Baltik, I did a similar project last summer and feel your pain. It wasn't fun!
My roof is vented but had no baffles, so the soffit was completely clogged with packed in fiberglass batts. I built baffles as described here and inserted them from the exterior removing the soffit vents as I went.
https://www.greenbuildingadvisor.com/article/site-built-ventilation-baffles-for-roofs
This baffle then provided the back for going around with 2-part spray foam all along the edges.
It was a lot of grubby work, but it's how I approached it.
Best of luck!
Brian
We also accessed the top plate from the outside. Contractor removed the old wood soffit. About 1-2" of air space to work with. Quick to install the rigid foam over the top plate. I like the idea of the built baffles (but we didn't do them).
When we insulated the exterior, we went up to the baffle so adding R10 over the face of the top plate.