Concern about vapor diffusion vents increasing summertime moisture in cathedral ceiling
I’m considering a vapor diffusion port on an existing unvented cathedral ceiling. I’m in climate zone 2A, hot and humid Gulf Coast. Existing insulation is fiberglass batts, but it’s impractical to re-roof or re-insulate.
A vapor diffusion port will allow vapor diffusion to move in both directions, with moisture going out in winter (as intended), but also coming in during summertime. If I use a/c for 7-8 months of the year and heat for 2-3 months, is there a risk that the outdoor air in summer (usually 90%+ humidity and around 80 degrees overnight) will diffuse into the drier cathedral ceiling space and condense on the 70-something-degree drywall ceiling? Do I risk creating a 7-8-month problem as serious as the potential 2-3-month problem I’m trying to solve?
“They” say vapor diffusion works in zones 1-3 to avoid wintertime condensation, but I don’t understand why vapor intrusion wouldn’t be a problem in the hotter months (i.e., most of the year), and the vapor diffusion studies seem to acknowledge higher humidity in the roofs in the summer.
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