How to Figure Out How Much Ventilation From a Hip Roof Vent

Vents

• 1

  Measure the width and length of a vent in inches. Vents in the eaves are intake vents and allow air to enter the attic space. Other vents in a hip roof are exhaust vents.

• 2

  Multiply the length of the vent by the width to obtain the net free area for the vent in square inches. A vent hole cut in the eave that is 15 inches long and 3 inches wide provides 45 inches of net free area.

• 3

  Repeat the process for all the intake and exhaust vents in the attic. Add the net free area for all the intake vents together. Add the net free area for all the exhaust vents together. The total net free area for the exhaust vents should equal or exceed the total net free area for the intake vents.

Calculating Ventilation Requirements

• 4

  Multiply the length of the attic by the width to obtain the square footage. Divide the square footage by 150 to calculate the net free area.

• 5

  Multiply the net free area by 144 to convert square feet to inches. The total net free area in inches is the minimum amount of venting required for the attic.

• 6

  Divide the net free area by two. This is the minimum number of square inches required for intake vents. The net free area of the exhaust vents must be equal to or exceed the net free area for the intake vents.