Attic Ventilation Formula

A discussion on attic ventilation isn t complete without going over the calculations to determine the minimum required net free ventilating area nfva.

Attic ventilation formula. 1 100 square inches of exhaust net free area needed 1 100 square inches of intake net free area needed. Since attic ventilation products are rated or specified by the manu. This means once we know the needed nfa for the entire attic 50 of it will be exhaust vents and 50 will be intake vents. 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. There should also be a 50 50 balance of attic venting and roof venting. According to their requirements you should have 1 square foot of attic ventilation per 300 sq ft of attic floor space. Ventilation of attic spaces is required by most building codes as well as by roofing material manufacturers and the national roofing contractors association nrca.

Calculating ventilation area of attic kitchen ventilation text. Calculate the total vent area needed multiply the length of the attic times the width in feet to find the attic area. It is the recommendation of the ravc that the attic ventilation system always be balanced. You can also contact your local municipality to check on building code in your area.

To find out how many soffit vents you need to install. Most building codes require a ratio of 1 150 ventilation space to attic floor space. Calculate or enter the square footage of the attic or area to be vented. Calculate the soffit vent area needed divide the total vent area by two to determine the soffit vent area.

The following is an example shown in the irc commentary for a simple gable roof using the 1 300 ratio. The house measures 30 feet by 50 feet.