How Much Attic Ventilation Is Needed

Since manufacturers of static ventilation products rate their products in square inches of nfa it will be necessary to multiply that value by 144 to determine the square inches required.

How much attic ventilation is needed.

The following are the requirements taken directly from the irc. 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. 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. Before we explore how to ventilate an attic space it is prudent to understand how much ventilation is needed.

Ventilation can be accomplished using various products and techniques. Up to 6 12 roof pitch use the standard formula as explained in this article. Calculate the total vent area needed. Generally as the roof pitch increases the volume inside the attic also increases along with the amount of needed attic ventilation.

Ideally there should also be plenty of soffit intake space their calculations recommend 336 net square inches of open soffit. Length x width of attic in feet 150 total sq. Generally speaking you need a ratio of 1 300 where for every 300 square feet of ceiling space you need 1 square foot of attic ventilation. The ventilation amount and opening size requirements can be found in section 806 roof ventilation of chapter 8 roof ceiling construction.

Attic ventilation works on the principle that heated air naturally rises primarily utilizing two types of vents. The majority of the requirements related to attic ventilation have not changed much from the previous editions. Ft divided by 150 equals 10 sq. Enter square footage calculate or enter the square footage of the attic or area to be vented.

A 50 x 30 attic would have a total area of 1 500 sq. Of total vent space 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. Here s a rule of thumb to follow.

According to the home ventilating institute hvi powered attic ventilators need to move a minimum of 700 cubic feet per minute cfm for 1 000 sq. Without exception you should talk to a professional to determine what your home requires. Ft of attic space for example 20 x 50 to be effective. Divide that area by 150 to determine the square feet of attic ventilation needed.

Ventilation of attic spaces is required by most building codes as well as by roofing material manufacturers and the national roofing contractors association nrca.