Roof Vent Calculator

The tool below will help you determine your minimum ventilation requirements.

The U.S. Department of Housing and Urban Development (HUD) sets standards for the Minimum Net Free Area. This figure is calculated based on the floor space of the attic (square footage). It is recommended that 50% of the Net Free Area is provided by Roof and Ridge Vents, with the remaining 50% provided by Under Eave Vents. FLAMCO manufactures all of the products necessary to properly ventilate your home.


Ridge Vent
180 sq inches per piece (10 LF)

Off-Ridge Vent
2′ Vent = 66 sq inches
4′ Vent = 138 sq inches
6′ Vent = 210 sq inches
8′ Vent = 282 sq inches

Hurricane Country Shingle Over Vent
4′ Vent = 72 sq inches

Hurricane Country II Shingle Over Vent
4′ Vent = 72 sq inches

Under Eave Vent
16″ x 4″ = 22 sq inches
16″ x 8″ = 58 sq inches
8′ Continuous = 61 sq inches