How to Calculate How Much Sofit Venting for Cathedral Ceilings

Like attics, cathedral ceilings in your home need the proper amount of ventilation to keep your house healthy. Since most cathedral ceilings don’t have room for an attic above them, the ceiling itself needs soffit vents installed in the rafters to keep the airflow in your home fluid. The number of vents you need to install will depend on the size of your ceiling and vents.

Measuring tape

Instructions

- 1
  Measure the size of the room with the cathedral ceiling and multiply the length by the width to get the number of square feet in the room. For example, a room that is 30 feet by 20 feet would be 500 square feet.
- 2
  Divide the number by 150 if you live in a new home or 300 if you live in a home build before the 1970s. This number is called the total net free ventilating area and will give you the amount of ventilated inches you need for your ceiling. For example, 500 divided by 150 is 3.3 square feet.
- 3
  Multiply this number by 144, the number of square inches in a square foot. For example, 3.3 multiplied by 144 is 480. This is the number of square inches you need to vent your cathedral ceiling.
- 4
  Divide the number of inches you need to vent by the square inches of the soffit vents you want to use. Most soffit vents are 56 square inches to 176 square inches. For example, 480 divided by 56 is 8.6, which you can round up to 9. You’d need nine soffit vents of 56 square inches for the ceiling.

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Ventilation