Roof Venting Ratio

Proper attic ventilation consists of a balance between air intake at your eaves soffits or fascias and air exhaust at or near your roof ridge.

Roof venting ratio.

In order to find the right calculator divide the attic floor space by 300 sq feet. And this guideline you ll need a minimum of. There should also be a 50 50 balance of attic venting and roof venting. The ratio of soffit intake to roof outlet should be at least 2 1 to avoid unnecessary these heat losses from the building.

Based on your 1100 sq. A serious error is a roof outlet vent net free area that exceeds the air inlets at lower roof edges or eaves. 1 square foot of net free vent area nfva per 150 feet of attic floor. If your roof is 1200 sq ft soffit floor space you will need 4 sq feet of roof ventilation.

1 square foot of nfva per 300 square feet of attic floor if a vapor barrier is installed on the ceiling below. Federal housing authority recommends a minimum of at least 1 square foot of attic ventilation evenly split between intake and exhaust for every 300 square feet of attic floor space.