What is the best attic ventilation method?

How the common methods rank

1. Soffit intake plus ridge vent. Air moves in at every eave bay and out along the whole peak, driven by both rising heat and wind, with no moving parts. This is what most shingle manufacturers recommend.
2. Soffit intake plus box vents. Works well when the ridge is short, as on many hip roofs. Place them high on the slope, within about 3 feet of the ridge measured vertically, and on the back slopes where possible.
3. Edge intake plus ridge vent. For homes with little or no overhang, intake vents installed at the roof edge under the shingles stand in for soffit vents.
4. Gable vents alone. Common on older homes. They ventilate the upper attic but leave the eaves stagnant. Acceptable if they meet the required area, but not ideal.
5. Powered fans. They can move a lot of air but risk pulling conditioned air out of the house and short circuiting other vents. Usually a last resort.

The other best method: no vents at all

When the HVAC system and ducts sit in the attic, as they do in many Georgia homes, a sealed attic with spray foam on the underside of the roof deck can outperform any vented design for energy use, because the ducts end up inside conditioned space. It must meet the unvented attic provisions of the code, and it is a whole house decision, not a roofing add-on.

Rules that apply to any vented method

• Size it to at least 1/300 of the attic floor with balanced intake and exhaust, or 1/150 if those conditions are not met.
• Use one type of exhaust per attic.
• Keep insulation out of the eaves with baffles.
• Send bath and dryer exhaust outdoors, never into the attic.

Compare exhaust choices in ridge vent vs box vents and review roof ventilation basics.