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.
Spray foam insulation on roof deck.
No interior class i vapor retarders e g plastic sheeting are installed on the ceiling side attic floor of the.
Unlike solid insulation products that require careful measurement cutting and fitting spray foam can cover even the most uneven surface instantly.
If you ve never heard the phrase hot roof i m sure you ve heard of an unvented attic.
This measure will convert a vented attic to a nonvented attic.
It s not coming from above the roof and it s not some new moisture source resulting from the spray foam.
The code allows for insulation directly to the underside of the structural roof sheathing providing the unvented attic is contained completely within the building thermal envelope.
Lstiburek takes blame for bad language.
Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls.
Spray foam insulation is actually a barrier between two areas of different temperatures so your attic would be the same temperature as the rest of your house even though it is cold outside.
In the northwest where foam has been sprayed directly to the underside of roof decks for over a decade the building officials interpret the code to require removal of existing insulation.
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.
Where wood shingles or shakes.
Inspect the existing roof shingles or roofing membrane for any deficiencies.
The installation steps are as follows.
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.
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.