Eave Vent Area To Floor Square Ft Ratio

Divide the square footage by 150 to calculate the area of ventilation needed since you need 1 square foot of vent space for each 150 square feet of attic space.

Eave vent area to floor square ft ratio.

That determines the total amount of net free area needed to properly ventilate the attic. 1 500 square feet 300 5 square feet. L x w in inches 144 area of vent in sq. Once attic square footage is known divide by 150 for the 1 150 ratio.

1 square foot of nfva per 300 square feet of attic floor if a vapor barrier is installed on the ceiling below. 30 feet x 50 feet 1 500 square feet. Remember the minimum area requirement when using a continuous system is a ratio of 1 300. Determine the total net free area required.

Ok so now we know the square footage of the attic area to be ventilated. If you have 3 000 square feet of attic space this equates to 20 square feet of ventilation needed. A 6 x 12 vent would equal 72 sq. So in our example we will divide the 1 500 square feet by 300.

For square or rectangular vents muliply the length times width of the vent space in inches then divide by 144 to convert into sq. Now let s figure out how much ventilation space we need. 40 x 25 1 000 square feet of attic area 2. In divided by 144 equals an area of 0 5 sq.

This ratio is required for modern insulated homes. See how simple that was. The irc adds that the nfva ratio can also be reduced to 1 300 if 50 to 80 of the required ventilation is located in the upper portion of the attic or cathedral ceiling and the rest is located at the eaves with the upper vents at least 3 feet above the lower.