Do I need soffit vents, and why does a soffit need to be vented?

Why intake matters as much as exhaust

Air in an attic moves as a loop. Rising heat and wind pull air out at the top, and replacement air has to come in somewhere. Low intake at the eaves makes that air sweep the underside of the whole roof deck before leaving. Many manufacturers recommend at least as much intake area as exhaust area.

When vented soffits are needed

• The roof has a ridge vent, box vents, turbines, or a power fan.
• The attic shows moisture or heat problems and the soffits are solid.
• You are reroofing and want the attic sized to code with balanced intake and exhaust.

When they are not

• The attic is sealed with spray foam under the roof deck. Then the soffits should be closed off from the attic.
• The house has little or no overhang. Intake can come from vents installed at the roof edge under the shingles instead.
• Gable vents are the whole ventilation system, though this is a weaker setup.

Do all soffit panels need to be vented?

No. You need enough net free area, spread along the eaves. Many homes alternate vented and solid panels or use center vented panels. Soffit over a porch or a closed rafter bay does not help, because no air path leads into the attic there.

Quick check

From inside the attic on a sunny day, look toward the eaves. If you see insulation packed tight with no light, the vents may be there but blocked. Baffles fix that. See roof ventilation basics and attic heat and shingles.