Condensation on underside of roof deck
My location is area code 13420.
My new construction is currently unheated and closed in. No insulation except for exterior wall foam sheathing. The rafters are open to the exterior at the top plate and the ridge is vented. When the temperature rises along with humidity the underside of the roof deck gets soaked with condensation. This happens in locations where the snow remains on the roof above, keeping the deck cold and enabling condensation to occur. Where the snow slides off the roof deck temp equalizes with exterior temp and the deck stays dry. My completed design is cape construction with 7/12 pitch and steel roofing. 5′ of the rafters – from the top plate to the intersection of collar ties – will get closed cell foam that will continue across the collar ties. Rafters get a 2″ vented space between the roof deck and foam. Ridge is vented and it’s height off the collar ties is 5′.
I don’t see this problem going away once the insulation is installed and the home heated, so besides insulating the underside of the roof deck are there any other solutions?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part