Attic Ventilation Formula

The following is an example shown in the irc commentary for a simple gable roof using the 1 300 ratio.

Attic ventilation formula.

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. If your roof is 1200 sq ft soffit floor space you will need 4 sq feet of roof ventilation. 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.

There should also be a 50 50 balance of attic venting and roof venting. Since attic ventilation products are rated or specified by the manu. Ventilation of attic spaces is required by most building codes as well as by roofing material manufacturers and the national roofing contractors association nrca. 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.

To find out how many soffit vents you need to install. The house measures 30 feet by 50 feet. You can also contact your local municipality to check on building code in your area. 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. It is the recommendation of the ravc that the attic ventilation system always be balanced. Calculate or enter the square footage of the attic or area to be vented. According to their requirements you should have 1 square foot of attic ventilation per 300 sq ft of attic floor space.

1 100 square inches of exhaust net free area needed 1 100 square inches of intake net free area needed. A discussion on attic ventilation isn t complete without going over the calculations to determine the minimum required net free ventilating area nfva.