Attic Ventilation Net Free Area

So for a 2400 sf attic space covered by roof you only need 8 sf of net free vent area to comply with the building code.

Attic ventilation net free area.

Let owens corning roofing help you calculate exactly how much ventilation you will need for a healthy and balanced attic with our 4 step ventilation calculator. Check with your building official for current code and a copy of the section regarding roof ventilation. The total net free area of the intake and exhaust must be balanced. This attic vent provides maximum airflow 72 square inches of net free ventilation area nfva without detracting from the aesthetics of the roof design.

The calculations before indicated that we needed 2 square feet of ridge or upper roof ventilation. If you do not have upper vents within 3 ft of the ridge then use 1 150. Eave vent gable vent roof jack soffit vent screen factor sf mesh sf w o louvers sf w louvers 1 4 or 1 2 1 0 2 0 1 8 1 25 2 25 1 16 2 0 2 0 nfa for common attic vents attic vents nfa. The net free area is always less than the actual area.

The passive vent net free area table gives the net free area ventilation for some common roof and gable passive vents. Screen factor sf adjusts for airflow obstructed by screens and louvers. Should you need to add more air intake ventilation to your attic simply determine the number of vents needed from the table based on your net free area requirements. Helpful hint for the 1 150 attic ventilation requirement simply double the amount of exhaust and intake calculated.

Besides the rated air ventilation area described by various vent product manufacturers other roof and vent opening details can significantly affect the actual airflow and level of under roof ventilation at a building. Two square feet equals 288 square inches. Of net free area of intake needed at or near the soffit. So we would need at least six metal vents in addition to the lower soffit ventilation to meet minimum ventilation requirements.

O hagin standard line of attic vents is available for contractor painting in 26 gauge g90 mill finish galvanized steel 0 032 aluminum 16 oz. Attic square footage 2 square inches of exhaust and square inches of intake net free area nfa needed. A normal metal pot vent produces only 50 squares inches of free net area. Comments opinion about statements of net free ventilation area of various roof venting products.

Calculate or enter the square footage of the attic or area to be vented.