How does a soffit vent work?
Short answer. A soffit vent is the intake half of attic ventilation: openings in the underside of the roof overhang let outside air into the attic at its lowest point, and that air rises along the underside of the roof deck to exit through ridge or box vents. It works only if a clear path exists from the soffit, over the top of the wall, and into the attic.
The air path
- Outside air enters through perforations or louvers in the soffit.
- It moves into the rafter bay above the exterior wall, between the top of the wall and the roof deck.
- It passes over the insulation, ideally through a baffle that keeps a clear channel.
- It rises along the underside of the decking as it warms and exits at the exhaust vents high on the roof.
Types of soffit vents
- Perforated vinyl or aluminum panels: small holes across the whole panel or just the center. The most common type on Georgia homes built in recent decades.
- Continuous strip vents: a slotted metal strip running along a wood soffit.
- Individual rectangular louvers: common on older homes with plywood soffits.
- Round plug vents: small screened circles drilled into soffit boards.
Why many soffit vents do not work
- Insulation blown or pushed tight against the roof deck at the eaves.
- Solid wood or plywood left behind when vented vinyl was installed over it.
- Paint clogging the perforations.
- Framing blocks or the top of a brick veneer wall closing the path.
- Debris, wasp nests, and pollen buildup on screens.
Checking yours
From the attic, look for daylight at the eaves. From outside, a smoke source held under the vent on a warm day should be drawn upward. If not, the vent is likely blocked. More in roof ventilation basics and attic heat and shingles.