Many people believe that the attic must be ventilated. They must be sure that spray foam is legal and cannot cause problems, before using it in the buildings with unvented roofs.
Residential Code, published in 2006, contains the section R806.4. This section allows to keep attics unvented, if some materials are applied for roof insulation. Spray foam is one of these materials. It has appropriate R-value, which allows keeping temperature of the foam surface above 44-46°F. This is necessary to prevent condensing of the surface.
Only air-impermeable materials are permitted by the Code. But the commonly used cellulose and fiberglass are not called air-impermeable. That is why they shouldn’t be used for roofs without ventilation.Foam spray bonds to the roof sheathing, resulting in cohesive and air-impermeable assembly, which is safe for building, it’s also permitted by International Residential Code. Unvented attics with spray foam may also be the salvation from the moisture problems. Temperature in the attics without ventilation is more comfortable for people and closer to interior temperature even in extreme temperature conditions.