How Much Attic Ventilation Is Needed

Always have a balanced ventilation system.

How much attic ventilation is needed.

The rule of thumb on the amount of vent space needed is approximately 1 sq. In other words the entire vent opening doesn t count as vented space. Of vent space for every 150 sq. In order to facilitate this exchange of warm and cool air the general rule of.

Most building codes require a ratio of 1 150 ventilation space to attic floor space. 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. And this guideline you ll need a minimum of. 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.

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. 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. That said air resistance and interference such as vent grates reduces the area of true ventilation. Divide that area by 150 to determine the square feet of attic ventilation needed.

Near ridge of the roof. So we would need at least six metal vents in addition to the lower soffit ventilation to meet minimum ventilation requirements. Based on your 1100 sq. Two square feet equals 288 square inches.

So if your attic is 1 500 sq. In no case should the amount of exhaust ventilation exceed the amount of intake ventilation. The calculations before indicated that we needed 2 square feet of ridge or upper roof 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.

Ft you divide that by 150 to get 10 sq. A normal metal pot vent produces only 50 squares inches of free net area. Taking advantage of this natural process referred to as passive ventilation is the most common way to vent an attic.