Attic Ventilation Ratio

Remember the minimum area requirement when using a continuous system is a ratio of 1 300.

Attic ventilation ratio.

1 300 ventilation ratio recommended. Without exception you should talk to a professional to determine what your home requires. 1 square foot of nfva per 300 square feet of attic floor if a vapor barrier is installed on the ceiling below. Allows cool dry air to enter the attic.

There should also be a 50 50 balance of attic venting and roof venting. Building codes vary. Always have a balanced ventilation system. 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.

Ventsure inflow intake vent. Ventilation of attic spaces is required by most building codes as well as by roofing material manufacturers and the national roofing contractors association nrca. Ok so now we know the square footage of the attic area to be ventilated. Most building codes require a ratio of 1 150 ventilation space to attic floor space.

In order to facilitate this exchange of warm and cool air the general rule of thumb suggests installing at least 1 sq. 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. The recommended ventilation ratio to provide for vented attic assemblies when an air barrier is present is the 1 300 ratio as specified by most building codes. So in our example we will divide the 1 500 square feet by 300.

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. According to their requirements you should have 1 square foot of attic ventilation per 300 sq ft of attic floor space. Choose one of the following products to meet the recommended intake nfva of 528 square inches. Now let s figure out how much ventilation space we need.

This is based principally on good historical experience and simple psychrometric analysis handegord giroux 1984. If your roof is 1200 sq ft soffit floor space you will need 4 sq feet of roof ventilation. Of vent for every 300 sq. That said air resistance and interference such as vent grates reduces the area of true ventilation.