Ventilation is the cheapest part of your roof

Roofs fail from the inside more often than the outside

In a climate that spends eight months near dew point, the water that destroys a roof assembly frequently comes from inside the house. Showers, cooking, and laundry push moist air into the attic, it condenses on the underside of cold sheathing, and the deck quietly loses strength for years before anyone sees a stain.

Balanced ventilation solves it: continuous intake at the eaves, continuous exhaust at the ridge, and roughly one square foot of net free area for every 150 square feet of attic floor. Intake is the half everyone forgets. A ridge vent with blocked soffits does not ventilate; it just pulls conditioned air out of your living room.

What it costs

On a typical reroof, adding proper intake and ridge exhaust is a few hundred dollars inside a five-figure project. It is the cheapest line on the estimate and the one most likely to decide whether the covering above it reaches its rated life.