Spray Foam Under Roof Sheathing

We have an insulation contractor in the area that does the expanding spray in place foam insulation.

Spray foam under roof sheathing. The formula in the building code is somewhat more conservative than dana s recommendation. To comply with the building code the spray foam layer should have an r value of r 15. Unlike solid insulation products that require careful measurement cutting and fitting spray foam can cover even the most uneven surface instantly. Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls.

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. Unvented roof strategies with spray polyurethane foam spf have been used since the mid 1990s to provide durable and efficient building enclosures. 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.

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. Foam insulation blown on bottom of roof sheathing. Take your pick as long as your building inspector approves. 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.

That s about 2 5 inches of closed cell spray foam assuming r 6 per inch. 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. It s not coming from above the roof and it s not some new moisture source resulting from the spray foam. If anyone has please contact me with evidence that being said open cell is a great product as well however in your case you.

Open cell spray polyurethane foam ocspf and closed cell spray polyurethane foam ccspf insulation sprayed to the underside of roof sheathing is a popular strategy for increasing roof insulation levels in all climate zones. Spray foam on underside of roof sheathing. 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.