An open cell foam about 0 5 pound density is the most cost effective way to insulate but any opening over 1 16 could cause the foam to expand out onto the roof.
Spray foam underside of roof deck.
Moisture generated indoors or that infiltrates into the home is responsible for the bulk of the moisture in an attic insulated with spray foam on the underside of the roof sheathing.
This construction approach was first used in the 1970s and it has been implemented much more widely since it was first included in the international code council s icc model building code in 2007 irc section 806 4.
No interior class i vapor retarders e g plastic sheeting are installed on the ceiling side attic floor of the.
Polyurethane or polystyrene spray foams can provide thorough coverage to roof rafters and attic walls in much less time than is needed for other materials.
A fillet application at the joint a one inch application across the whole cavity as might be used in a flash and batt application and a three inch application filling the bay.
How spray foam should be installed on the underside of the roof decking the unvented attic space is completely within the building s thermal envelope.
In our neck of the woods closed cell foam costs about 56 more than open cell.
Unlike solid insulation products that require careful measurement cutting and fitting spray foam can cover even the most uneven surface instantly.
University of florida researchers tested three levels of spray foam roof underside retrofit.
Where wood shingles or shakes.
It s not coming from above the roof and it s not some new moisture source resulting from the spray foam.