Roofing Giant · Free tool
An attic that cannot breathe cooks shingles from below, traps moisture and raises cooling bills. This calculator applies the International Residential Code ratio to your attic floor area and tells you how much intake and exhaust you need, in square inches of net free area and in real vents.
Why balance matters
Intake first
Exhaust vents cannot pull air the soffits do not supply. Blocked or painted-over soffit vents are the most common ventilation failure we find on inspections.
Do not mix exhaust types
Ridge vents with turbines or power fans short-circuit: the strongest vent pulls air from the weakest one instead of from the soffits.
Baffles at the eaves
Insulation pushed into the eaves blocks intake. Baffles keep a clear channel from soffit to attic.
Signs your attic is under-ventilated
- Shingles curling or losing granules early on south and west slopes
- Attic temperatures far above outdoor temperature on summer afternoons
- Rusty nail tips, frost or condensation on the underside of the deck in winter
- Ice dams, mold or a musty smell
- A manufacturer warranty claim denied for “improper ventilation”
Ventilation is checked on every 30-point inspection and corrected as part of a replacement. The code references are on the roofing codes page.
We measure intake and exhaust and tell you what your attic needs.Ventilation check with every inspection