Attic Ventilation Formula

Let s use the following simple ranch house for an example.

Attic ventilation formula.

The following is an example shown in the irc commentary for a simple gable roof using the 1 300 ratio. Calculate the soffit vent area needed divide the total vent area by two to determine the soffit vent 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.

There should also be a 50 50 balance of attic venting and roof venting. A discussion on attic ventilation isn t complete without going over the calculations to determine the minimum required net free ventilating area nfva. 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. Calculating ventilation area of attic kitchen ventilation text.

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. Use our easy 3 step attic ventilation calculator to determine your attic square footage and ventilation needs. 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. Calculate the total vent area needed multiply the length of the attic times the width in feet to find the attic area.

Calculate or enter the square footage of the attic or area to be vented. Since attic ventilation products are rated or specified by the manu. To find out how many soffit vents you need to install. 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. According to their requirements you should have 1 square foot of attic ventilation per 300 sq ft of attic floor space.