Formula For Proper Attic Ventilation

Calculate the total vent area needed multiply the length of the attic times the width in feet to find the attic area then divide by 150 to find the total square feet of vent space needed.

Formula for proper attic ventilation.

Remember the minimum area requirement when using a continuous system is a ratio of 1 300. According to the national roofing contractors association nrca a power vent with an airflow rate of 1 0 cubic foot per minute per square foot of attic space measured at the attic floor is generally considered to be equivalent to a 1 150 ventilation ratio. Now let s figure out how much ventilation space we need. After that find out the vent s nfa as rated by the manufacturer.

See how simple that was. Next multiply the 4 square feet into cubic inches. So in our example we will divide the 1 500 square feet by 300. Of attic space you need 1 sq.

Ventilation of attic spaces is required by most building codes as well as by roofing material manufacturers and the national roofing contractors association nrca. Calculate or enter the square footage of the attic or area to be vented. Cool air in hot air out. 1 100 square inches of intake net free area needed.

Ok so now we know the square footage of the attic area to be ventilated. 1 500 square feet 300 5 square feet. 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. Ensuring your home has the proper attic ventilation according to these guidelines however can save yourself the stress and hassle of an emergency roof repair.

Most building codes require a ratio of 1 150 ventilation space to attic floor space. It states that for every 150 sq. 2 200 2. 1 cubic foot is 12 x 12 144 cubic inches.

Proper attic ventilation consists of a balance between air intake at your eaves soffits or fascias and air exhaust at or near your roof ridge. In our case the required 4 vents for the 1200 sq ft house multiply the 144 cubic inches by 4 576 cubic inches. 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. 1 100 square inches of exhaust net free area needed.

Tips for assessing your needs. Length x width of attic in feet 150 total sq. There is a generally agreed upon formula that you can apply for balanced attic ventilation known as the 1 150 rule.