Spray Foam Under Roof Sheathing

Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls.

Spray foam under roof sheathing.

If anyone has please contact me with evidence that being said open cell is a great product as well however in your case you. To comply with the building code the spray foam layer should have an r value of r 15. The anecdotes and data are enough to provide a few rules of thumb for designers and builders who want to install spray foam on the underside of roof sheathing. It s not coming from above the roof and it s not some new moisture source resulting from the spray foam.

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. Underside of roof decks since the late 60s early 70s and to my knowledge i have not seen or heard of a rotted substrate under and conditions closed cell foam was applied. Foam insulation blown on bottom of roof sheathing. The formula in the building code is somewhat more conservative than dana s recommendation.

Unlike solid insulation products that require careful measurement cutting and fitting spray foam can cover even the most uneven surface instantly. Spray foam on underside of roof sheathing. We have an insulation contractor in the area that does the expanding spray in place foam insulation. Open or closed cell spray foam is applied to the underside of the roof sheathing and additional fiberglass or cellulose insulation is blown in as a cost saving method for meeting high insulation requirements and filling in the cavity space between the rafters to the ceiling deck.

Take your pick as long as your building inspector approves. Install spray foam insulation along the underside of the roof deck to create an insulated unvented attic which can provide a conditioned space for hvac equipment that is located in the attic. 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. Lstiburek takes blame for bad language.

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. On houses with the roof system forming the ceiling in the upstairs such as in a 1 1 2 story house he recommends spraying the foam directly to the bottom of the roof sheathing. Increasingly building scientists are investigating why osb roof sheathing on many spray foam insulated roofs stays damp for months at a time.