Attic Ventilation & Ridge Vent Calculator
Calculate Net Free Vent Area (NFVA) under the 1:300 code rule, continuous ridge vent footage, and soffit intake vents.
Input Parameters
Enter dimensions and specifications to estimate materials.
Total Net Free Area Required
Soffit Vents Needed
6vents
Ridge Vent Length
15linear ft
Intake NFA (50% low)
268.8sq in
Exhaust NFA (50% high)
268.8sq in
Attic Floor Area
1120sq ft
Code Rule Applied
IRC 1/300 Balanced Ventilation Standard
Material estimates include recommended trade waste buffer. Always confirm dimensions on site prior to ordering.
How The Calculation Works
Formulas, material coverage assumptions, waste buffers, and rounding standards.
Required ventilation is expressed as Net Free Area — the actual open area of a vent after the screen and louvre are deducted, which is typically far less than the vent's physical size.
The total is split evenly between low intake at the soffits and high exhaust at the ridge. Balance is what makes the system work: exhaust without matching intake simply pulls conditioned air up out of the house.
Ridge vent is converted to linear feet assuming roughly 18 sq in of NFA per foot, and soffit vents at about 50 sq in each for a standard 16" × 8" undereave vent.
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Frequently Asked Questions
Practical installation guidance and purchasing tips for attic ventilation & ridge vent calculator.