Eave Vent Area To Floor Square Ft Ratio

Most local building codes require compliance with either the 1 150 method or the 1 300 method exception refer to local code.

Eave vent area to floor square ft ratio.

Remember the minimum area requirement when using a continuous system is a ratio of 1 300. For square or rectangular vents muliply the length times width of the vent space in inches then divide by 144 to convert into sq. A 6 x 12 vent would equal 72 sq. If you have 3 000 square feet of attic space this equates to 20 square feet of ventilation needed.

40 x 25 1 000 square feet of attic area 2. 1 500 square feet 300 5 square feet. Ok so now we know the square footage of the attic area to be ventilated. See how simple that was.

Determine the total net free area required. 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. 150 6 6 square feet of total net free area 3. Once attic square footage is known divide by 150 for the 1 150 ratio.

So in our example we will divide the 1 500 square feet by 300. This ratio is required for modern insulated homes. 1 square foot of nfva per 300 square feet of attic floor if a vapor barrier is installed on the ceiling below. 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.

These methods dictate that one 1 square foot of ventilation is provided for every 150 or 300 square feet of attic floor space. 30 feet x 50 feet 1 500 square feet. In divided by 144 equals an area of 0 5 sq.