Attic Ventilation Ratio

So in our example we will divide the 1 500 square feet by 300.

Attic ventilation ratio. 1 300 ventilation ratio recommended. 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. If your roof is 1200 sq ft soffit floor space you will need 4 sq feet of roof ventilation.

According to their requirements you should have 1 square foot of attic ventilation per 300 sq ft of attic floor space. Ok so now we know the square footage of the attic area to be ventilated. 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.

Building codes vary. Of vent for every 300 sq. You can also contact your local municipality to check on building code in your area. 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.

Remember the minimum area requirement when using a continuous system is a ratio of 1 300. 1 square foot of nfva per 300 square feet of attic floor if a vapor barrier is installed on the ceiling below. This is based principally on good historical experience and simple psychrometric analysis handegord giroux 1984. Always have a balanced ventilation system.

Now let s figure out how much ventilation space we need. There should also be a 50 50 balance of attic venting and roof venting. 1 square foot of net free vent area nfva per 150 feet of attic floor. 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 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. Allows cool dry air to enter the attic. Ventilation of attic spaces is required by most building codes as well as by roofing material manufacturers and the national roofing contractors association nrca. That said air resistance and interference such as vent grates reduces the area of true ventilation.