Attic Venting Formula

The ridge vent is installed on the peak with nails and shingled over for aesthetic purposes.

Attic venting formula.

Ridge vents are one of the easiest ways to meet roof venting requirements. Every formula for attic ventilation i ve seen says 1 sq ft of ventilation is required for every 300 sq ft of attic floor space. Jones has an attic space that measures 23 feet by 48 feet. Building codes typically echo the administration s guidelines.

That number is divided by 2 so that the ventilation is equally distributed between the soffit and the ridge. 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. Remember the minimum area requirement when using a continuous system is a ratio of 1 300.

Now let s figure out how much ventilation space we need. Ben erickson september 28 2010 at 8 03 am. 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. This yields a total area of 1 104 square feet.

Calculate or enter the square footage of the attic or area to be vented. The federal housing administration recommends 1 square foot of attic ventilation for every 150 square feet of attic space. Standard attic vents like af 50 s ventilation fans or solar powered attic fans. Jones takes this measurement and divides it by 150 for a total of 7 36 square feet of ventilation space that is needed.

So in our example we will divide the 1 500 square feet by 300. Nfa is the unobstructed area through which air can pass through a vent usually measured in square inches. Ventilation manufacturers assign an nfa value to the non motorized vents they make.