Since drywall has a permeance of 0.02 liter/sec – m at 75 PA is ever possible to have sheathing dry to the interior of the home?
JoeUSAF
| Posted in General Questions on
When constructing a new home most professionals recommend not have impermeable insulation or other materials on both sides of the sheathing. It is recommended that the sheathing should be able to dry to the exterior or interior of the home. If foil faced polyiso rigid foam is used on the exterior of the plywood sheathing and 6 inches of open cell foam and drywall is used on the interior of the home, will this configuration allow the home to dry to the interior? Considering the permeability of drywall will it ever allow drying to the interior of the home with any type of insulation?
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Replies
Joseph,
You are confusing an air leakage rate with a vapor permeance rating.
Drywall is an air barrier. Its air leakage rate is a bit under 0.02 liter/sec - m2 at 75 PA.
Drywall is vapor-permeable, however. Unpainted drywall has a vapor permeance of 49.7 perms.
Inward drying occurs by vapor diffusion, not air movement.