Soffit vent vs roof vent: what is the difference?
Short answer. A soffit vent is an intake vent under the roof overhang that brings outside air into the attic; a roof vent is an exhaust vent near the top of the roof that lets hot, moist air out. They are partners, not alternatives: a vented attic needs both, with intake at least equal to exhaust.
Roles
- Soffit vent: low, sheltered from rain by the overhang, and able to feed every rafter bay.
- Roof vent: high, near the ridge, removing the warmest air. Types include ridge vents, box vents, turbines and powered fans.
Can a vent on the roof be intake?
Yes, one type: the edge intake vent installed on the roof surface at the eave for homes without soffits. That is what people usually mean by a soffit vent on the roof. It sits at the lowest shingle courses, not up high. A box vent placed low on the slope will act partly as intake, but that is no substitute for real soffit intake and can let in rain.
What happens with one but not the other
- Roof vents only: exhaust pulls air through ceiling leaks from the house, adding humidity and wasting conditioned air.
- Soffit vents only: air enters but has nowhere to go, so the upper attic stays hot.
Balance
Split the total required net free area roughly in half, then give intake a little extra if you can. Too much exhaust relative to intake is the more harmful imbalance. See roof ventilation basics and ridge vent vs box vents.