How do you add ventilation to an attic, and how much does adding attic ventilation cost?
Short answer. To add ventilation to an attic, start with intake: open or add soffit vents and install baffles so air can enter at the eaves. Then add exhaust high on the roof, usually a ridge vent on gable roofs or box vents on short hip ridges, and close any competing exhaust so the new vents work as one system.
Ways to add intake
- Open what is there: pull insulation back from the eaves and install rafter baffles.
- Cut in soffit vents: strip vents or round plug vents in wood soffits, or swap solid vinyl panels for vented ones, making sure any solid wood behind them is opened.
- Edge intake vents: for homes with no overhang, vents installed at the roof edge under the shingles bring air in at the eave line.
Ways to add exhaust
- Ridge vent: remove the ridge cap, cut a slot, install the vent, and recap. Best on gable roofs.
- Box vents: add individual vents high on the back slopes, within about 3 feet of the ridge measured vertically.
- Hip vents: add exhaust length on hip roofs with short ridges.
- Powered fans: a last resort, and only with plenty of intake.
Order of operations
- Calculate the requirement: attic floor area divided by 300, times 144, split evenly between intake and exhaust.
- Inventory what you have and its ratings.
- Fix intake first, then exhaust.
- Close gable vents or extra exhaust that would short circuit the new system.
- Make sure bath and dryer exhaust go outdoors, not into the attic.
Rough costs
Clearing intake and adding baffles is the cheapest step. Cutting in soffit vents and retrofitting a ridge vent each commonly run several hundred dollars, more for long or high eaves and steep ridges. During a roof replacement, adding a ridge vent or edge intake costs far less because the roof is already open. See roof ventilation basics and roof replacement cost in Georgia.