How Much Attic Ventilation Is Needed

In order to facilitate this exchange of warm and cool air the general rule of.

How much attic ventilation is needed.

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. Two square feet equals 288 square inches. Ventilation can be accomplished using various products and techniques. Taking advantage of this natural process referred to as passive ventilation is the most common way to vent an attic.

Most building codes require a ratio of 1 150 ventilation space to attic floor space. Divide that area by 150 to determine the square feet of attic ventilation needed. In other words the entire vent opening doesn t count as vented space. That said air resistance and interference such as vent grates reduces the area of true ventilation.

So we would need at least six metal vents in addition to the lower soffit ventilation to meet minimum ventilation requirements. The rule of thumb on the amount of vent space needed is approximately 1 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. Of vent space for every 150 sq.

Always have a balanced ventilation system. Based on your 1100 sq. Before we explore how to ventilate an attic space it is prudent to understand how much ventilation is needed. And this guideline you ll need a minimum of.

The calculations before indicated that we needed 2 square feet of ridge or upper roof ventilation. Ft you divide that by 150 to get 10 sq. Near ridge of the roof. This shortcut conveniently calculates the 2015 international residential building code minimum irc section r806 roof ventilation 1 which states in part 1 square foot of net free area for every 150 square feet of attic floor space with the attic defined as length x width floor of the attic.

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. In no case should the amount of exhaust ventilation exceed the amount of intake ventilation. To determine the static ventilator net free area nfa needed for your attic space determine the area of the attic in square feet.