Spray Foam Insulation Under Roof Deck

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.

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. 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. 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 attic is unvented for instance no ridge vent exists.

I have a conditioned attic currently insulated with r19 fiberbatts between the rafters. 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. Despite the advantages of using spray foam under the roof deck there are some potential risks. 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.

Closed cell foam has been applied underside of roof decks since the late 60s early. 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. The primary risks are rainwater leaks condensation from diffusion air leakage and built in construction moisture. The attic will be a conditioned space and i m planning to apply spray foam insulation to the underside of the roof sheathing.

A double wide mobile home on blocks with a crawl space and dirt floor. Should i put any membrane or the like on the underside of the roof sheathing before spraying the foam in. The biggest benefit of spray foam insulation is its air sealing quality so if air is infiltrating into a spray foam attic then the installers missed some spots and need to go back and make it right. 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.

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 source. Unlike solid insulation products that require careful measurement cutting and fitting spray foam can cover even the most uneven surface instantly. 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.