Attic Ventilation Formula

According to their requirements you should have 1 square foot of attic ventilation per 300 sq ft of attic floor space.

Attic ventilation formula.

Since attic ventilation products are rated or specified by the manu. Ok to determine how much ventilation area you need for your house all you need to know is the square foot area of the attic to be ventilated. Ventilation of attic spaces is required by most building codes as well as by roofing material manufacturers and the national roofing contractors association nrca. You can also contact your local municipality to check on building code in your area.

1 100 square inches of exhaust net free area needed 1 100 square inches of intake net free area needed. If your roof is 1200 sq ft soffit floor space you will need 4 sq feet of roof ventilation. Most building codes require a ratio of 1 150 ventilation space to attic floor space. Calculate the soffit vent area needed divide the total vent area by two to determine the soffit vent area.

Calculate the total vent area needed multiply the length of the attic times the width in feet to find the attic area. Let s use the following simple ranch house for an example. Use our easy 3 step attic ventilation calculator to determine your attic square footage and ventilation needs. The house measures 30 feet by 50 feet.

Calculate or enter the square footage of the attic or area to be vented. It is the recommendation of the ravc that the attic ventilation system always be balanced. A discussion on attic ventilation isn t complete without going over the calculations to determine the minimum required net free ventilating area nfva. 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.

There should also be a 50 50 balance of attic venting and roof venting. The following is an example shown in the irc commentary for a simple gable roof using the 1 300 ratio.