Net Free Area Tables

/Net Free Area Tables
Net Free Area Tables2016-11-28T19:08:26+00:00

Net Free Area Tables

1:150 Ratio-no Moisture Barrier | 1:300 Ratio-w/ Moisture Barrier

1:150 Ratio-no Moisture Barrier

1:150 ratio: Net Free Area Table-Use when no Moisture Barrier is installed.

The MINIMUM attic ventilation required by the Building Codes is 1 square foot of total net free area per 150 square feet of attic when no moisture barrier is used.

A Balanced System requires soffit ventilation in an amount equal to or greater than the amount of ridge ventilation. See soffit vent manufacturer’s information on the Net Free Area provided by soffit vent product.

Attic Area (SF) Minimum NFA (SF) Exhaust NFA (SF) Length of Roof Saver (FT) Intake NFA (SF)
1000 6.67 3.33 31.6 3.33
1100 7.33 3.67 34.7 3.67
1200 8.00 4.00 37.9 4.00
1300 8.67 4.33 41.1 4.33
1400 9.33 4.67 44.2 4.67
1500 10.00 5.00 47.4 5.00
1600 10.67 5.33 50.0 5.33
1700 11.33 5.67 53.7 5.67
1800 12.00 6.00 56.8 6.00
1900 12.67 6.33 60.0 6.33
2000 13.33 6.67 63.2 6.67
2100 14.00 7.00 66.3 7.00
2200 14.67 7.33 69.5 7.33
2300 15.33 7.67 72.6 7.67
2400 16.00 8.00 75.8 8.00
2500 16.67 8.33 39.5 8.33
2600 17.33 8.67 41.1 8.67
2700 18.00 9.00 42.6 9.00
2800 18.67 9.33 44.2 9.33
2900 19.33 9.67 45.8 9.67
3000 20.00 10.00 47.4 10.00
See soffit vent manufacturers instructions for NFA calculation.

1:300 Ratio-w/ Moisture Barrier

1:300 ratio: Net Free Area Table-Use when Moisture Barrier is installed

The MINIMUM attic ventilation required by the Building Codes is 1 square foot of total net free area per 300 square feet of attic when a moisture barrier is installed.

A Balanced System requires soffit ventilation in an amount equal to or greater than the amount of ridge ventilation. See soffit vent manufacturer’s information on the Net Free Area provided by soffit vent product.

Attic Area (SF) Minimum NFA (SF) Exhaust NFA (SF) Length of Roof Saver (FT) Intake NFA (SF)
1000 3.33 1.67 15.8 1.67
1100 3.67 1.83 17.4 1.83
1200 4.00 2.00 18.9 2.00
1300 4.33 2.17 20.5 2.17
1400 4.67 2.33 22.1 2.33
1500 5.00 2.50 23.7 2.50
1600 5.33 2.67 25.3 2.67
1700 5.67 2.83 26.8 2.83
1800 6.00 3.00 28.4 3.00
1900 6.33 3.17 30.0 3.17
2000 6.67 3.33 31.6 3.33
2100 700 3.50 33.2 3.50
2200 7.33 3.67 34.7 3.67
2300 7.67 3.83 36.3 3.83
2400 8.00 4.00 37.9 4.00
2500 8.33 4.17 39.5 4.17
2600 8.67 4.33 41.1 4.33
2700 9.00 4.50 42.6 4.50
2800 9.33 4.67 44.2 4.67
2900 9.67 4.83 45.8 4.83
3000 10.00 5.00 47.4 5.00
See soffit vent manufacturers instructions for NFA calculation.