How to Calculate Proper Attic Ventilation

Proper attic ventilation lets air circulate through your attic. The air circulation deters the buildup of excessive heat and moisture. You can achieve attic ventilation in several ways. Fans, vents, skylights and windows that open can all help ventilation. The method you choose may depend on how you use your attic space.

Calculating Attic Ventilation Needs

As a general rule, every 150 square feet of attic space requires 1 square foot of ventilation. Windows do not always remain open, so fans and vents are your best bet. You might consider ridge vents, box and dome vents, gable fans and vents, or soffit vents.

Using the above calculations, we find that an area that is 600 square feet should have 4 square feet of operable attic ventilation. To fill this ventilation requirement, you could use four box vents (1 square foot each) or one long, narrow ridge vent (4 total square feet).

Improper Attic Ventilation

Without proper air circulation, moisture can build up in your attic. The moisture may lead to rotting drywall and insulation. In addition, since heat rises, air needs to flow in and out of the attic to draw out the heat as much as possible.

To avoid potential problems, measure the square footage as described above and choose a method of attic ventilation that can fulfill your needs.