CSLB C-39 Roofing ContractorFlashing, Ventilation and InsulationHard
A contractor is installing closed-cell spray polyurethane foam directly against the underside of the roof sheathing to create a conditioned, unvented attic assembly. According to standard building practice for this assembly type, what is required regarding attic ventilation?
- AVentilation requirements double because spray foam traps excess moisture in the attic
- BGable vents alone are sufficient since ridge vents would compromise the foam seal
- CNo soffit or ridge ventilation is required because the roof deck itself becomes part of the building's thermal and air barrier
- DStandard 1/150 ventilation must still be provided through soffit and ridge vents
Show answer & explanationAnswer & explanation
Correct answer: C. No soffit or ridge ventilation is required because the roof deck itself becomes part of the building's thermal and air barrier
When closed-cell spray foam is applied directly to the roof deck, the attic becomes part of the conditioned building envelope (an 'unvented attic assembly'). Because the foam acts as both insulation and an air/vapor barrier at the roof deck, the traditional soffit-to-ridge ventilation pathway is unnecessary and is typically omitted.
Why the other options are wrong
- A. Unvented spray foam assemblies control moisture through the air seal, not increased ventilation.
- B. Gable vents would be unnecessary and could disrupt the sealed conditioned space.
- D. Contradicts the purpose of an unvented, conditioned attic assembly.
Unvented Conditioned Attic Assembly
Applying closed-cell spray foam directly to roof sheathing creates a sealed, conditioned attic that becomes part of the building envelope, eliminating the need for soffit/ridge ventilation.
- Foam applied directly to underside of roof deck
- Attic becomes part of conditioned space
- Standard 1/150 or 1/300 ventilation not required
Memory trick: Seal the deck, skip the vents — the attic joins the house.