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How to Calculate Attic Ventilation
Formula
Proper attic ventilation prevents moisture damage, ice dams, and excessive heat buildup. The standard rule is 1 sq ft of net free vent area per 150 sq ft of attic floor.
Balanced ventilation means equal intake (soffit vents) and exhaust (ridge or roof vents). The 1/300 rule applies when intake and exhaust are balanced.
Common use cases:
- Attic vent installation planning
- Building code compliance
- Moisture and ice dam prevention
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