How to Calculate Eave Ventilation Area

Attic ventilation keeps a continual flow of fresh air through an unconditioned space. The air reduces moisture buildup in the attic, preventing mold, mildew and fungus from growing. It also prevents the wood from rotting due to excessive moisture, and mitigates the chances of ice dams forming in winter. The amount of ventilation must be evenly distributed between the eave and ridge vents. This ensures a balanced flow of air through both systems.

Things You'll Need

• Measuring tape
• Calculator

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Instructions

1. • 1

     Divide your attic into square sections and measure each section's width and length with a measuring tape.

   • 2

     Multiply the individual sections' width by their length and add the figures together to determine the total area.

   • 3

     Divide this area by 300. The ratio of ventilation-to-attic space must be at least 300:1. Divide the result by 2. The answer is the required square feet of eave ventilation.