Should my attic be ventilated, or is mine an exception?
Short answer. Most attics should be ventilated, but there are real exceptions: attics sealed with spray foam on the underside of the roof deck, conditioned attics built on purpose to house HVAC equipment, and some low-slope or cathedral assemblies with rigid foam above the deck. Those are designed to be unvented, and adding vents to them can create moisture problems.
Vent it if
- Insulation sits on the attic floor as batts, blown fiberglass or cellulose.
- The roof deck is bare wood when you look up from the attic.
- The attic was built with soffit and ridge or box vents, even if some are now blocked.
Do not vent it if
- Spray foam covers the underside of the deck and the gable walls, sealing the attic. Georgia builders and retrofitters often do this when the air handler and ducts sit in the attic, to bring them inside the conditioned space. The residential code's unvented attic section sets specific insulation requirements for these.
- Rigid foam is installed above the deck on a cathedral or low-slope roof.
Gray areas worth a professional look
- Spray foam added to a previously vented attic while the old soffit or ridge vents were left open.
- Vaulted ceilings without vent channels in each rafter bay.
- Bonus rooms with knee walls that split the attic into small, unconnected pockets.
Roofing over a spray foamed deck
Some shingle manufacturers set specific requirements or warranty conditions for shingles over unvented assemblies, so check the warranty terms before reroofing. Leaks are also harder to spot when foam hides the deck, which makes regular roof inspections more valuable. Read roofing warranties explained and roof ventilation basics.