How much attic ventilation does a Georgia roof need?

Attic and Ventilation · Updated October 13, 2026

Short answer. Georgia's residential code (2024 IRC section R806.2) requires 1 square foot of net free vent area for every 150 square feet of attic, or 1 per 300 when 40 to 50 percent of that area is exhaust within 3 feet of the ridge and the rest is low intake. Shingle makers such as GAF require ventilation that meets those minimums, and the system only works when soffit intake roughly balances ridge exhaust.

What attic ventilation is for

A vented attic has two jobs: get rid of moisture and get rid of heat. Moisture is the less obvious one. Showers, cooking, laundry and even breathing put water vapor into the house, and some of it drifts up through ceiling gaps into the attic. GAF's field guide for installers describes what happens when it stays there: the vapor condenses on the cold underside of the roof deck, plywood delaminates, OSB swells, framing warps, insulation loses effectiveness and mold follows. On a clear winter night in North Georgia, the underside of a roof deck can be the coldest surface in the house.

Heat is the familiar one. The same GAF guide notes that attics can reach 165 degrees or more and roof decks can pass 170 degrees in summer. Ventilation alone will not make a hot attic cool, but a stagnant one is worse.

Both jobs rely on the same airflow: cooler outside air enters low, at the soffits or eaves, and warm, moist air leaves high, at or near the ridge. Wind pressure and the natural rise of warm air keep it moving.

What the code requires

Georgia's residential code is the 2024 International Residential Code with Georgia amendments, effective January 1, 2026. The Georgia amendments add an attic access rule for attics with equipment but do not change the ventilation section. Section R806 requires:

Cross ventilation for every separate enclosed attic or rafter space, with openings protected from rain, birds and rodents. Openings must be between 1/16 and 1/4 inch, or covered with screening that meets those sizes.
The 1/150 rule: net free ventilating area of at least 1/150 of the vented space.
The 1/300 exception: the area may drop to 1/300 if at least 40 and no more than 50 percent of it is in the upper part of the attic, no more than 3 feet below the ridge, with the rest in the bottom third. (A second condition about vapor retarders applies only in climate zones 6 through 8, which do not include Georgia.)
Clearance at the eaves: insulation and blocking cannot block airflow at eave vents, and there must be at least a 1-inch space between insulation and the roof sheathing at the vent.

The code also allows unvented attics, typically with spray foam under the roof deck, when a list of insulation and vapor conditions is met. That is a different design and should be planned with the insulation contractor, not improvised during a reroof.

Doing the math

Net free area is the open space a vent actually lets air through, after louvers, screens and baffles. Vent makers print it on the package, either per piece or per linear foot. To size a system, measure the attic floor area (usually the footprint of the heated space below), divide by 150 or 300, and convert square feet to square inches by multiplying by 144.

Attic floor area	Total at 1/150	Total at 1/300	1/300 split, exhaust and intake
1,200 sq ft	1,152 sq in	576 sq in	288 high, 288 low
1,800 sq ft	1,728 sq in	864 sq in	432 high, 432 low
2,400 sq ft	2,304 sq in	1,152 sq in	576 high, 576 low

The split shown is 50 percent high and 50 percent low, the balanced design GAF teaches and the upper limit the code allows for exhaust under the 1/300 option. GAF's own example: a 1,200-square-foot attic needs 576 square inches, with 288 at the ridge and 288 at the soffits. If a ridge vent provides 18 square inches per linear foot, only 16 feet of a 40-foot ridge needs to be cut open.

Balance: why intake usually decides

GAF calls intake arguably the most important part of the system, and its field guide says ridge exhaust should never exceed soffit intake. Exhaust vents cannot pull air through an attic that has no way for air to enter; a power fan in that situation works too hard and burns out, and static vents just sit there. Common intake problems on Georgia homes include:

Vented soffit panels installed over solid wood with no holes cut behind them.
Blown-in insulation packed into the eaves, which baffles are meant to prevent.
Soffit vents painted over or clogged with dust and spider webs.
Houses with closed soffits or little overhang, which need a different intake product, such as a vented drip edge or a rooftop intake vent.

The other common mistake is mixing exhaust types, such as a ridge vent plus box vents or a power fan, over one attic. That can short-circuit airflow; our guide to ridge vents vs box vents explains why.

Manufacturer warranty requirements

Shingle makers write ventilation into their own requirements, not just the code. GAF's field guide for installers notes that most major shingle manufacturers, GAF included, require ventilation meeting FHA minimum requirements, the same 1/150 and 1/300 ratios the code uses, and it teaches installers to size intake and exhaust to those numbers. A Florida Solar Energy Center review of the research found that most shingle makers say their warranties will be voided if the underside of the roof deck is not vented. In practice, that means an attic that fails the minimums hands the manufacturer an easy reason to question a claim about early shingle failure.

Researchers have found that ventilation changes shingle temperature only slightly, a few percent, compared with shingle color. That does not make it optional. It is the moisture control, and it is a warranty condition. Our guide to attic heat and shingles covers the temperature side.

When to fix it

The easiest time is during a roof replacement, when the deck is open: ridge slots can be cut to the right length, intake added, and old mismatched vents removed. Signs it needs attention include rusty nail tips or dark staining on the underside of the deck, musty smells or mold in the attic, frost on nails on cold mornings, and upstairs rooms that never cool off.

Getting it right

Robust Roofing, a GAF certified contractor with a 5.0 rating across 66 Google reviews, installs to the manufacturer's requirements, ventilation included, and covers its workmanship with a 50-year labor warranty. Its free roof inspection documents the current roof with photos, and its explainer on why Georgia roofs fail from the inside walks through the attic problems it sees most.

Common questions

What is net free area?

Net free area is the actual open space a vent lets air pass through after its louvers, screens and baffles are accounted for. Vent manufacturers print it on the product, per piece or per linear foot.

Can an attic have too much ventilation?

Too much exhaust relative to intake causes problems. GAF says ridge exhaust should never exceed soffit intake, because unbalanced exhaust can pull air from the wrong places, including rain through other vents or conditioned air from the house.

Should bathroom fans vent into the attic?

No. A bath fan that dumps into the attic feeds it exactly the moisture the ventilation system is trying to remove. Duct bath and kitchen fans all the way outside.

Does the 1/300 rule apply in Georgia?

Yes, when 40 to 50 percent of the vent area is high exhaust within 3 feet of the ridge and the rest is low intake. The vapor retarder condition in the code only applies in climate zones 6 through 8.

Does attic ventilation make shingles last longer?

Its effect on shingle temperature is small, but it controls moisture that can rot the deck, and shingle manufacturers require it for warranty coverage.