Roof Ventilation Explained: Ridge Vent, Turbines, and Why Mixing Them Fails
How intake and exhaust ventilation actually work, why mixing ridge vents with turbines short-circuits your attic, and how to size ventilation correctly.
Bad ventilation cooks shingles from underneath and voids most manufacturer warranties. Good ventilation is boring, quiet, and adds 5–8 years of shingle life.
How balanced ventilation works
Cool air enters at the soffit (intake). Warm air exits at the ridge (exhaust). The ratio is 1:1 — every square inch of intake matched by a square inch of exhaust.
Code (IRC R806) requires 1 sq ft of net-free ventilation area per 300 sq ft of attic floor, split intake/exhaust.
Ridge vent — the default in 2026
Continuous vent along the ridge, covered by ridge cap shingles. Nearly invisible, no moving parts, no leaks when properly installed.
Turbines and box vents — legacy exhaust
Fine on their own, but never mix with a ridge vent on the same attic. When you do, the ridge vent becomes an intake, air short-circuits, and half the attic gets no airflow at all.
Powered attic fans — usually the wrong answer
Solar or electric attic fans pull conditioned air out of the house through ceiling gaps, raising cooling bills. DOE studies consistently show they cost more to run than they save.
How to check yours
Attic temperature within 15°F of outside on a hot day = good. 30°F+ hotter = under-ventilated. Look for blocked soffit vents (insulation stuffed against them is the #1 cause).
Frequently Asked Questions
- Do I need ventilation with a spray-foam attic?
- No. Closed-cell spray foam creates an unvented, conditioned attic — different code path (IRC R806.5). Ridge vents are actively harmful in that case.
- How much does adding a ridge vent cost during a roof replacement?
- $400–$900 on an average roof. Almost always worth it if you're already tearing off — extends shingle life measurably.
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