How Much Attic Ventilation Is Required

Furthermore nrca also rec ommends the amount of ventila.

How much attic ventilation is required.

As an example in an attic that is 30 feet by 20 feet you would have 600 square feet of floor area. 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. 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. Ventilation can be accomplished using various products and techniques.

For large volume attics such as where roof slopes are greater than 8 12 designers also should consider increasing the amount of attic ventilation to account for the additional volume of attic space. 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. So in our example we will divide the 1 500 square feet by 300. 1 500 square feet 300 5 square feet.

Now let s figure out how much ventilation space we need. Figure 1 soffit to ridge attic ventilation. Divide that area by 150 to determine the square feet of attic ventilation needed. Before we explore how to ventilate an attic space it is prudent to understand how much ventilation is needed.

The following are the requirements taken directly from the irc. Remember the minimum area requirement when using a continuous system is a ratio of 1 300. See how simple. The ventilation amount and opening size requirements can be found in section 806 roof ventilation of chapter 8 roof ceiling construction.

Ok so now we know the square footage of the attic area to be ventilated. According to the fha federal housing administration us for every 300 square feet of attic floor area you should have at minimum one square foot ventilation. So how much ventilation should you have. Is this too much ventilation.

I have received several questions and comments since writing about attic ventilation. Of attic space 1 150 ventilation ratio measured at the attic floor level ceiling. Enter square footage calculate or enter the square footage of the attic or area to be vented. 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.

Ventilation of attic spaces is required by most building codes as well as by roofing material manufacturers and the national roofing contractors association nrca. Without exception you should talk to a professional to determine what your home requires.