Roof Ventilation Calculator
Estimate attic ventilation needs with a quick NFVA rule-of-thumb. Enter your attic floor area, choose the 1:150 standard or 1:300 balanced rule, and see total net free vent area plus intake and exhaust targets so you can plan soffit and ridge vents faster.
Inputs
Split
Disclaimer: This is a rough sizing tool. Ventilation requirements vary by roof design, climate zone, and local code. Always confirm NFVA requirements with your local building authority and vent product ratings.
Results
Total NFVA
1,440 in²
10 ft² of net free vent area
Intake target
720 in²
Soffit or low intake vents.
Exhaust target
720 in²
Ridge, gable, or roof vents.
Assumptions
- Uses rule-of-thumb ratios (1:150 or 1:300) for attic ventilation.
- Balanced split assumes equal intake and exhaust when selected.
- NFVA varies by product; use rated net free area, not rough opening.
Next Steps
- ✓ Confirm roof area with the roofing squares calculator
- ✓ Get ordering context from the roofing calculators guide
Example
An attic of 1500 sq ft at a 1:150 rule needs about 1,440 in² of total NFVA, split into 720 in² intake and 720 in² exhaust when balanced.
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