Frost in the attic after air sealing
I own a 1960s ranch in Minneapolis, and last year I spent a considerable amount of time in the attic performing air sealing. I pulled up almost every square inch of insulation and got all of the interior stud wall top plates, plumbing penetrations, electrical penetrations, and drywall joints. I also sealed at the exterior wall top plate. also sealed the attic hatch with weatherstrip. Now, I didn’t have a “before” blower door test done, but the “after” blower door test didn’t show any leakage through the dropped soffit, kitchen vent, or attic hatch. (ACH50 of 5.1).
Today is a cold day here, about -3 F. I went up to the attic to see how it looked and I saw frost on the roofing nails and in some spots of the sheathing. Needless to say, I was disappointed. So, I got out my foam gun, and crawled over to the spots with frost, expecting to find a nice size air leak that I missed. But when I moved the insulation….nothing. Just drywall, solid. No obvious air leak. So, I’m stuck.
At this air temperature, is frost normal? If it’s a sign of continued air leak, how should I track it down?
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