Do you need attic ventilation with spray foam, and does a spray foam attic need ventilation?
Short answer. No. When spray foam is applied directly to the underside of the roof deck, the attic becomes an unvented, semi conditioned space, and the soffit and ridge vents are closed rather than left open. If spray foam is used only on the attic floor, the attic above it is still a vented attic and needs normal ventilation.
Two different designs
- Foam on the roof deck: insulation and air seal move to the roofline. The attic sits inside the building's thermal envelope, which is why this works well in Georgia homes with HVAC equipment and ducts in the attic. Vents must be sealed, or outside air bypasses the foam.
- Foam on the attic floor: used for air sealing the ceiling. The attic remains outside the envelope and still needs balanced intake and exhaust.
Code requirements for unvented attics
IRC Section R806.5 sets the conditions, including insulation in direct contact with the underside of the roof deck and an assembly that controls condensation, typically air impermeable insulation such as spray foam at the minimum R-value required for the climate zone. Your building department will look for this on a permit.
Things to know before foaming
- Shingle warranty. Manufacturers have published positions on unvented assemblies; check yours before installing foam.
- Leak detection. Foam can hide small roof leaks until the decking is damaged. Fix all leaks first and consider replacing an aging roof before foaming.
- Humidity. Building scientists often recommend a small supply of conditioned air or dehumidification in a sealed attic, especially in a humid climate like Georgia's.
- Inspections and insurance. Home inspectors and insurers sometimes ask about foam because it makes the deck hard to see.
The mistake to avoid
Foaming the deck and leaving the ridge and soffit vents open undermines both systems. If you foam, the ventilation gets closed properly. See roof ventilation basics and OSB vs plywood roof decking.