Spray Foam Insulation Under Roof Deck

The code allows for insulation directly to the underside of the structural roof sheathing providing the unvented attic is contained completely within the.

Spray foam insulation under roof deck.

With enough closed cell spray foam under the deck or enough rigid above the deck interior moist air can t condense if the there is no condensation you don t need drying thus no need to vent. Despite the advantages of using spray foam under the roof deck there are some potential risks. But spray foam insulation used at the underside of the roof deck would need to be covered by a thermal barrier and intumescent coatings are commonly used. No airsealing hence i want to remove the fiberbatts and spray 3 inches of closed cell spray foam in before putting the fiberbatts back in place.

The primary risks are rainwater leaks condensation from diffusion air leakage and built in construction moisture. A double wide mobile home on blocks with a crawl space and dirt floor. Unlike solid insulation products that require careful measurement cutting and fitting spray foam can cover even the most uneven surface instantly. 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.

Should i put any membrane or the like on the underside of the roof sheathing before spraying the foam in. Closed cell foam has been applied underside of roof decks since the late 60s early. 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. The roofing materials are installed and consist of timberline shingles and full coverage ice and water barrier the entire roof.

The amount of closed cell spray foam or rigid insulation is somewhere between 20 to 50 of the r value of the overall cavity insulation depending on. The movement of air into indirect conditioning of an unvented attic is a slow gradual process that will not be noticeable by occupants and typically will not put any strain on the hvac system. The spray foam can also serve as the thermal and vapor control layers in both new and retrofit construction. The attic is unvented for instance no ridge vent exists.

I have a conditioned attic currently insulated with r19 fiberbatts between the rafters. Regarding open cell foam under a roof deck how about under a floor. Sloped roof with cavity spray foam insulation sprayed on underside of roof deck and covered with a sprayed on thermal or ignition barrier coating over the spray polyurethane foam insulation if necessary based on the material properties of the spray polyurethane foam or as required by code source.