How Much Attic Ventilation Is Needed

A 50 x 30 attic would have a total area of 1 500 sq.

How much attic ventilation is needed.

Attic ventilation works on the principle that heated air naturally rises primarily utilizing two types of vents. Intake vents located at the lowest part of the roof under the eaves allow cool. Up to 6 12 roof pitch use the standard formula as explained in this article. 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.

Without exception you should talk to a professional to determine what your home requires. The ventilation amount and opening size requirements can be found in section 806 roof ventilation of chapter 8 roof ceiling construction. Of total vent space needed. So how much ventilation should you have.

Before we explore how to ventilate an attic space it is prudent to understand how much ventilation is needed. Calculate the total vent area 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. Ventilation can be accomplished using various products and techniques.

Divide that area by 150 to determine the square feet of attic ventilation needed. The majority of the requirements related to attic ventilation have not changed much from the previous editions. Ft of attic space for example 20 x 50 to be effective. 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. The following are the requirements taken directly from the irc. 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. Ft divided by 150 equals 10 sq.

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. 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. Here s a rule of thumb to follow. Ventilation of attic spaces is required by most building codes as well as by roofing material manufacturers and the national roofing contractors association nrca.

Enter square footage calculate or enter the square footage of the attic or area to be vented.