Attic Ventilation Formula

It states that for every 150 sq.

Attic ventilation formula. 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. Attic area including eave soffit 104 x 124. Of attic space you need 1 sq. Now let s figure out how much ventilation space we need.

Tips for assessing your needs. According to the national roofing contractors association nrca a power vent with an airflow rate of 1 0 cubic foot per minute per square foot of attic space measured at the attic floor is generally considered to be equivalent to a 1 150 ventilation ratio. The example below uses this exception and the calculation is based on a 100 x120 building with a hip roof and 2 overhangs on all sides. So for an attic that s 1 000 square feet you would divide 1 000 by 150 to calculate that 6 6 square feet nfa of ventilation would be required.

Assembly ventilation coalition ravc that all roofing professionals have a basic understanding of the attic ventilation calculations necessary to help the system fight heat in the summer moisture in the winter and ice dams in cold climates. There should also be a 50 50 balance of attic venting and roof venting. If your roof is 1200 sq ft soffit floor space you will need 4 sq feet of roof ventilation. Let owens corning roofing help you calculate exactly how much ventilation you will need for a healthy and balanced attic with our 4 step ventilation calculator.

Exception 1 allows you to only ventilate 1 300 th of the attic area if 50 to 80 of the ventilation occurs at least 3 above eave or cornice vents. To achieve a balanced system half that amount is intake and the other half is exhaust so each should be 3 3 square feet or 475 square inches. 30 feet x 50 feet 1 500 square feet. Ventilation manufacturers assign an nfa value to the non motorized vents they make.

Attic ventilation calculations made easy 84 24 3 7 2 212 768 56 x 84 56 x 39 3 2 2 120 0 3 8 5 3 3. Nfa is the unobstructed area through which air can pass through a vent usually measured in square inches. Attic square footage 2 square inches of exhaust and square inches of intake net free area nfa needed. 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.

Calculate or enter the square footage of the attic or area to be vented. Calculation formula there is a generally agreed upon formula that you can apply for balanced attic ventilation known as the 1 150 rule.