What are the residential attic ventilation requirements?
Short answer. Under Section R806 of the International Residential Code, which Georgia enforces through its state amended edition, an enclosed attic needs cross ventilation with net free vent area of at least 1/150 of the attic floor, or 1/300 when 40 to 50 percent of the vents are high exhaust and the rest are low intake. Vent openings must be screened, and insulation must leave at least a 1 inch air space at the eave vents.
The requirements, section by section
Section numbers below follow recent editions of the International Residential Code.
- R806.1, ventilation required: enclosed attics, and enclosed rafter spaces where ceilings are attached directly to the rafters, need cross ventilation for each separate space, with openings protected against rain. Openings must have a least dimension between 1/16 and 1/4 inch; larger openings need corrosion resistant mesh, hardware cloth or perforated vinyl within that range.
- R806.2, minimum area: net free area of 1/150 of the vented space. It can drop to 1/300 when 40 to 50 percent of the required area is in upper vents within 3 feet of the ridge, measured vertically, with the rest at the eaves. An added vapor retarder condition applies only in the coldest climate zones, not Georgia.
- R806.3, insulation clearance: insulation cannot block eave or cornice vents, and there must be at least 1 inch of space between insulation and roof sheathing at the vent.
- R806.4, installation: vents installed according to the manufacturer's instructions and the code's roof and wall weather protection rules.
- R806.5, unvented attics: allowed only when specific insulation conditions are met, typically air-impermeable insulation such as spray foam against the deck.
How it applies in Georgia
Georgia's mandatory residential code is the 2024 International Residential Code with Georgia amendments, effective January 1, 2026. Cities and counties enforce it through permits, and some add local amendments. A reroof permit may not trigger a ventilation review, but shingle warranties still expect code compliant ventilation, so ask your roofer to show the math on the estimate. See roofing permits in Georgia and roofing warranties explained.