What are the roof and attic ventilation requirements for different roof types?
Short answer. The baseline requirement is the same everywhere under the residential code: net free vent area of 1/150 of the vented space, or 1/300 when balanced with 40 to 50 percent high exhaust. How you meet it changes with the roof: gable attics use soffit intake and ridge exhaust, hip roofs often need extra high vents, cathedral ceilings need a vent channel in every rafter bay, and sealed spray foam roofs follow separate unvented rules.
By roof type
- Gable roof over open attic: the easiest case. Continuous soffit intake on both eaves, a ridge vent along the peak, gable vents closed.
- Hip roof: intake on all four eaves is plentiful, but exhaust is limited by the short ridge. Supplement with static or off-ridge vents near the peak where the manufacturer allows.
- Cathedral or vaulted ceiling: code treats each enclosed rafter space as needing ventilation. Each bay needs an open channel at least 1 inch deep from soffit to ridge, or the assembly must be built unvented with the required insulation.
- Bonus room over a garage: knee walls and sloped ceilings divide the attic into pockets. Each pocket needs intake and exhaust, or the sloped portion needs channels.
- Low-slope roof with no attic: usually built unvented with insulation above the deck.
- Conditioned attic: no vents, with insulation at the roof deck under the unvented attic rules.
Requirements that apply to all
- Vent openings screened between 1/16 and 1/4 inch.
- Insulation kept at least 1 inch below the deck at eave vents.
- Vents installed per the manufacturer and protected from rain.
- Bath, kitchen and dryer exhaust discharged outdoors, never into the attic or a soffit.
Georgia's current code is the 2024 International Residential Code with state amendments, enforced locally. Read roof ventilation basics and roofing permits in Georgia.