How to Determine Ventilation for Roofs With Roof Peak Vents

Proper attic ventilation involves both roof peak vents and roof gable vents. The roof peak vents are known as exhaust vents since they allow air to flow out of the attic space. In order to find out how much ventilation you need, you have to figure out how big your attic is. The Federal Housing Administration suggests that for every 150 to 300 square feet of attic space, you'll need one square foot of attic ventilation. These are known as the 1/150 and 1/300 rules. Half of that ventilation space needs to be in outtake vents, such as roof peak vents.

Things You'll Need

Measuring tape

Instructions

- 1
  Measure the length and width of your attic's floor space. To determine the square footage of your attic, multiply the width by the length. For example, a 30-x-40-foot attic is 1,200 square feet.
- 2
  Divide the square footage measurement by 150 for a new home, or 300 for an older home. For example, 1,200 divided by 150 is eight. This is the total number of square feet of ventilation you need in your attic.
- 3
  Convert the amount of attic ventilation from square feet to square inches, since most attic vents are measured in inches. Multiply the number of total square feet by 144, which is the number of inches per square foot. In this example, eight multiplied by 144 is 1,152.
- 4
  Divide the total number of vents by two to figure out how many intake and outtake vents you need. For example, 1,152 divided by two is 576 square inches of roof peak vents.
- 5
  Measure the size of the roof peak vent and multiply its width by its height to get the total number of square inches of ventilation it can provide. To get the total number of rook peak vents for your attic, divide the square inches of roof peak ventilation you need by the amount of ventilation provided by the vent. For example, if you have a vent that's 8 by 10 inches, it provides 80 inches of vent space. Divide 576 by 80 to get 7.2, which you can round up to eight roof peak vents.

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