Attic Ventilation Calculator
Find out how much net free area your attic actually needs — using the standard 1:150 rule that Oklahoma building officials and shingle manufacturers use. Enter your attic's floor square footage, pick your vent types, and get the exact intake, exhaust, ridge vent, and box vent counts for your home.
Ventilation Requirements Calculator
All controls are sized for comfortable use on a phone. Results update instantly as you change inputs.
Total net free area required for your attic
Intake needed (soffit)
0 soffit vents
Exhaust needed (ridge / box)
0 linear ft of ridge vent
Ridge Vent vs Box Vent: Which for Oklahoma?
Both are legitimate exhaust options. Here's how they compare on a Tulsa-area roof.
| Consideration | Ridge Vent | Box Vent |
|---|---|---|
| Net free area | ~18 sq in per linear foot — a 40′ ridge delivers ~720 sq in | Typically 50–144 sq in per vent; needs many units to match a ridge |
| Airflow pattern | Continuous, even exhaust along the full ridge — no dead zones | Localized exhaust; vents must be spaced evenly to avoid pockets |
| Oklahoma heat | Best for hot climates; moves the most hot air with natural convection | Works, but only with enough vents and matching soffit intake |
| Leak risk | One continuous flashing line when installed with a proper ridge shingle cap | Each vent is a potential leak point; more penetrations on the deck |
| Best for | Simple hip and gable roofs with a full ridge line | Roofs without a continuous ridge, or retrofits where the ridge can't be cut |
Whichever you choose, the math is the same: exhaust area must never exceed intake area. A ridge vent without enough soffit vents is a common — and expensive — mistake.
Need a Second Opinion on Your Attic?
Proof Construction offers free, no-obligation attic and roof evaluations for Tulsa-metro homeowners. We'll measure your actual vent area, check your soffit intake, and tell you straight whether your attic is under-ventilated — and what fixing it costs.
CALL (918) 734-4444Licensed & insured • OK License CIB #80004070 • BBB A+ Accredited • Owens Corning Preferred Contractor
Attic Ventilation FAQ
The standard rule is 1 square foot of net free area for every 150 square feet of attic floor area — the 1:150 rule. A 1,500 sq ft attic needs 10 sq ft of total net free vent area, split between intake and exhaust. The 1:300 ratio is allowed only when ventilation is balanced — half at the eaves or soffits and half at the ridge — with a vapor retarder installed.
Yes. At minimum, intake and exhaust should be balanced 50/50, and many roofers recommend slightly more intake (a 60/40 intake-to-exhaust split) in hot climates like Oklahoma. Too much exhaust with too little intake pulls conditioned air out of your living space and can cause moisture problems in the attic.
For most Oklahoma roofs, a continuous ridge vent is the better exhaust choice: it runs the full ridge length, provides more net free area, and creates fewer potential leak points than multiple box vents. Box vents work on simple roofs where a ridge vent isn't practical, but they need careful spacing to avoid dead zones.
Unventilated attics in Oklahoma routinely hit 140–160°F in July and August. That trapped heat radiates into your living space, drives up cooling bills, and can void shingle warranties by cooking the shingles from underneath. Proper intake-plus-exhaust airflow keeps the attic near outdoor temperatures.
The attic will pull replacement air from wherever it can — usually down through ceiling cracks and recessed lights, which draws conditioned air out of your home. That wastes energy in summer and can pull moisture into the attic in humid weather. Ventilation only works when intake and exhaust are balanced.