What is a soffit vent?

From below, look for continuous perforated panels running the length of the eave, or individual rectangular grilles, commonly 4 by 16 inches, spaced every few feet between rafter tails. The more useful check happens inside on a bright day. Crawl to the low edge where the roof deck meets the top of the exterior wall and look for daylight around the perimeter. Insulation packed tight against the sheathing instead of daylight is the single most common ventilation defect in American attics. The plastic or foam chutes stapled between rafters, called baffles or rafter vents, are what hold that 1-inch to 2-inch air channel open.

Ventilation is sized by net free area. Code generally asks for 1 square foot of vent per 150 square feet of attic floor, or 1 per 300 when the venting is split roughly half intake and half exhaust with a ceiling vapor retarder in place. Intake is the half people skip. A continuous 2-inch vent strip supplies around 9 square inches of net free area per lineal foot, so the arithmetic usually works out as long as the vents are open. When they are buried, three things follow. Summer attic temperatures climb and cook the shingles from below, which most warranties treat as a maintenance failure. Winter moisture condenses on the sheathing and grows mold. And the ridge vent starts drawing makeup air out of the house through recessed lights and ceiling gaps, dragging indoor humidity up with it, which is also how ice dams get worse.

Treat this as an inspection item, best done in fall. From the attic, pull insulation back off the eaves, add baffles anywhere they are missing at $2–5 apiece, and confirm you can see light at the edges once the work is done. From the ground, check that nobody painted the perforations shut during the last exterior job, and knock out wasp nests. Do it while you are already examining the soffit itself, and look at the exhaust side in the same trip (what a ridge vent is), because intake and exhaust only work as a matched pair.