How to Calculate Soffit & Fascia
Soffit area: Perimeter x Overhang width (ft)
Fascia: Perimeter in linear feet, divided by board length
Vent area: Attic sq ft / 150 (code minimum NFA)
Ventilation Requirements
- 1/150 rule: 1 sq ft of Net Free Area per 150 sq ft of attic (no vapor barrier)
- 1/300 rule: 1 sq ft per 300 sq ft if vapor barrier present and balanced intake/exhaust
- Soffit vents should provide at least 50% of total attic ventilation