Spray Foam Underside Of Roof Deck

It would be better to use a closed cell 2 pound density foam because it doesn t expand as much as open cell and is more likely to fill voids but not go through them.

Spray foam underside of roof deck.

Where wood shingles or shakes. 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. In our neck of the woods closed cell foam costs about 56 more than open cell.

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. No interior class i vapor retarders e g plastic sheeting are installed on the ceiling side attic floor of the. It s not coming from above the roof and it s not some new moisture source resulting from the spray foam. 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.

Lstiburek takes blame for bad language. University of florida researchers tested three levels of spray foam roof underside retrofit. 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.