Attic Ventilation Ratio

Now let s figure out how much ventilation space we need.

Attic ventilation ratio.

Of vent for every 300 sq. 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. 1 300 ventilation ratio recommended.

Choose one of the following products to meet the recommended intake nfva of 528 square inches. So in our example we will divide the 1 500 square feet by 300. Allows cool dry air to enter the attic. 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.

Remember the minimum area requirement when using a continuous system is a ratio of 1 300. 1 square foot of net free vent area nfva per 150 feet of attic floor. In order to facilitate this exchange of warm and cool air the general rule of thumb suggests installing at least 1 sq. Building codes vary.

If your roof is 1200 sq ft soffit floor space you will need 4 sq feet of roof ventilation. This is based principally on good historical experience and simple psychrometric analysis handegord giroux 1984. There should also be a 50 50 balance of attic venting and roof venting. That said air resistance and interference such as vent grates reduces the area of true ventilation.

Ok so now we know the square footage of the attic area to be ventilated. According to their requirements you should have 1 square foot of attic ventilation per 300 sq ft of attic floor space. 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. You can also contact your local municipality to check on building code in your area.

Without exception you should talk to a professional to determine what your home requires. Always have a balanced ventilation system. The following product options will allow you to achieve an intake nfva of 528 square inches. 1 square foot of nfva per 300 square feet of attic floor if a vapor barrier is installed on the ceiling below.