Attic Ventilation Basics: Why Your Roof Needs to Breathe

Attic ventilation moves outside air through the attic space, typically in at soffit vents near the eaves and out at a ridge or roof vents near the peak. The goal is to keep the attic close to outdoor temperature, which does two things: it stops warm, moist indoor air that's leaked upward from condensing on cold roof sheathing, and it keeps the underside of the roof deck cold enough that snow on the shingles doesn't melt and refreeze at the eaves as an ice dam.

Codes typically set a minimum net free ventilation area relative to the insulated ceiling area below, split between intake and exhaust. Insulation that's been pushed into the soffit and blocked the intake path is one of the most common ways a technically-vented attic stops actually working — the vents exist, air just can't move through them anymore.