Ventilation component
What is a soffit vent?
The intake half of attic ventilation: the slots, strips and perforations under the eave that let cool outside air in so the ridge vent has something to exhaust.
Updated September 12, 2026 · Every figure links to its source · Sources
DefinitionComponentAlso called: eave vent, intake vent, continuous soffit vent
Soffit vent — a ventilation opening set into the soffit at the eave — as a continuous strip vent, individual rectangular or round vents, or perforated soffit panel — through which outside air enters the attic; the 2021 IRC, Section R806 counts eave and cornice vents as the lower part of the required attic ventilation and requires a clear air path above the insulation at each one.
What it is
Air enters an attic at the eaves and leaves at the ridge, and the soffit vents are the entrance. Three forms are common: a continuous strip vent, a narrow aluminium or vinyl louvered channel that runs the full length of the eave; individual vents, rectangular or round louvers set into a solid soffit every few feet; and perforated soffit panel, vinyl or aluminium soffit with holes across its width, which vents the whole overhang. Each is rated by its net free area — the open area after louvers and screen are subtracted — which is the number that counts toward the code.
The IRC, Section R806.2 sets the total: net free area of at least one 150th of the attic floor area, or one 300th when 40 to 50 percent of it is high in the attic (at least three feet above the eave vents) and the rest is at the eaves. Section R806.3 then protects the intake: where eave vents are installed, the insulation must not block the airflow, and a clear space of at least one inch must be kept between the insulation and the roof sheathing — in practice, a baffle or chute stapled between the rafters at every vented bay.
Why it matters
A ridge vent without intake is a slot in the roof. The stack effect that carries warm, moist air out at the ridge only works if cooler air can come in below; block the soffits and the ridge vent draws from the house instead, through every ceiling gap, pulling conditioned air and moisture into the attic. The commonest way soffits get blocked is an insulation upgrade pushed to the eaves without baffles; the second is a soffit replacement with solid panel; the third is paint. Mould on the underside of the sheathing, frost in the attic in winter, and ice dams are the signs.
The directory's roof ventilation calculator turns an attic's area into the intake and exhaust area required and the number of vents of a given rating that provide it; the directory's how-to on ridge vents covers the exhaust side that the soffits feed.
What it costs and who does it
Adding soffit vents is priced per vent or per foot of strip vent, plus baffles per rafter bay if the insulation must be pulled back, and is done by roofing contractors, insulation contractors (as part of an attic air-sealing and insulation job) and siding or trim contractors replacing soffit. On a re-roof it is a small line and the natural time to balance the system with the new ridge vent. The directory's roof repair cost guide describes how such small items are estimated.
Frequently asked questions
Short answers; the sections above carry the detail and the sources.
How many soffit vents do I need?
Can insulation block soffit vents?
Do I need soffit vents if I have gable vents?
Next step
Find a roofer who does this
Intake, exhaust and baffles are one job; ask the contractor to quote all three. The directory lists roofing contractors by state and city.
Sources
- 2021 International Residential Code, Chapter 8: Roof-Ceiling Construction — International Code Council (ICC)