Attic Ventilation Calculator
Attic Ventilation
Calculate the net free vent area needed for your attic.
Formula
NFA = Attic Area / Ventilation Ratio (150 or 300)
Frequently Asked Questions
What is the 1/150 ventilation rule?
It means 1 sq ft of vent area per 150 sq ft of attic without a vapor barrier.
Should intake and exhaust be balanced?
Yes, split vent area evenly between soffit intake and ridge exhaust.