Formula For Proper Attic Ventilation

Cool air in hot air out.

Formula for proper attic ventilation.

There is a generally agreed upon formula that you can apply for balanced attic ventilation known as the 1 150 rule. 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. Most building codes require a ratio of 1 150 ventilation space to attic floor space. 2 200 2.

Ventilation of attic spaces is required by most building codes as well as by roofing material manufacturers and the national roofing contractors association nrca. The next step is to select a suitable exhaust vent and intake vent that fits the roof design for best performance and best aesthetics. In order to find the right calculator divide the attic floor space by 300 sq 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.

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. Now let s figure out how much ventilation space we need. You can also contact your local municipality to check on building code in your area. Calculate or enter the square footage of the attic or area to be vented.

So in our example we will divide the 1 500 square feet by 300. Length x width of attic in feet 150 total sq. 1 100 square inches of intake net free area needed. 1 100 square inches of exhaust net free area needed.

See how simple that was. After that find out the vent s nfa as rated by the manufacturer. 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.

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. 1 500 square feet 300 5 square feet. 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. Tips for assessing your needs.

In our case the required 4 vents for the 1200 sq ft house multiply the 144 cubic inches by 4 576 cubic inches. Next multiply the 4 square feet into cubic inches. Ok so now we know the square footage of the attic area to be ventilated.