How do attic vents work, and what does each type do?
Short answer. Attic vents work as a team: intake vents low on the roof, usually in the soffits, let outside air in, and exhaust vents high on the roof let warm, moist air out. Air moves between them because warm air rises and because wind creates pressure differences across the roof, and some vents add a fan to force the flow.
Intake vents
- Soffit vents: perforated panels, continuous strips, or individual louvers under the eaves.
- Edge intake vents: low profile vents at the roof edge, under the first courses of shingles, for homes without overhangs.
Passive exhaust vents
- Ridge vent: a continuous vent along the peak over a slot in the decking, usually hidden under cap shingles. It exhausts at the highest point along the whole ridge.
- Box or static vents: individual hooded openings near the ridge. Simple and reliable, but they vent in spots.
- Hip vents: similar to ridge vents but installed along hips, used on roofs with short ridges.
- Gable vents: louvers in the end walls. They act as both intake and exhaust depending on wind direction.
Wind and powered exhaust
- Turbines: wind spins the vanes, which pulls air up and out. They move more air in wind and very little when it is calm.
- Power and solar fans: motors pull air out on a thermostat or humidistat. They need generous intake or they draw air from the house.
How they work together
The system works best when intake and exhaust are balanced, intake is spread along the eaves, and only one type of exhaust is used per attic. Mixing exhaust types lets air loop between the exhaust vents instead of entering at the soffits. Sizing comes from the code: at least 1/150 of the attic floor area in net free vent area, or 1/300 with properly placed high exhaust. More in roof ventilation basics and ridge vent vs box vents.