Proper way to insulate an old attic?
I am helping to insulate a friend’s attic in Milwaukee, Climate Zone 6. The house is 100 years old, balloon frame with stucco. Attic floor is lathe and plaster. We would like to remove the fiberglass insulation, clean the attic floor, seal holes/top plate, then spray 2″ closed cell spray foam to air seal the lathe and plaster. After that fill in blown cellulose to R-60.
My question, if we are sealing off the top plate of the exterior walls, are we in danger of causing a condensation problem in those walls. They may or may not have insulation we are unsure, but the house is very drafty. Moisture has been moving through the walls for 100 years, and with the top plate sealed there will be less air movement so should be less moisture infiltration. I can imagine a little condensation on the exterior side of the top plate, where the cold be coming from the side through the stucco and the attic insulation will not help keep that edge warm.
I really want to spray foam to help air-seal the attic, but I obviously don’t want to cause a moisture issue. I think it will be fine, just trying to find a second opinion.
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