Attic Ventilation Calculator

Why NFVA Matters

Proper attic ventilation is arguably the most critical component of a new roof installation. If a roof cannot "breathe", extreme heat will bake the shingles from the inside out, dramatically shortening their lifespan. Furthermore, poor ventilation instantly voids almost all manufacturer warranties (like GAF, Owens Corning, and CertainTeed).

The 1:300 vs 1:150 Rule

• The 1:150 Rule: The general building code states you need 1 square foot of ventilation for every 150 square feet of attic space.
• The 1:300 Rule: You can cut the requirement in half (1:300) IF your ventilation is perfectly balanced (50% intake at the eaves/soffits, and 50% exhaust at the ridge) AND the ceiling has a Class I or II vapor retarder.

A balanced system is crucial. If you install massive ridge vents (exhaust) but the soffit vents (intake) are painted shut or blocked by insulation, the ridge vent will pull conditioned air straight out of the living space, causing energy bills to skyrocket.