Roof Ventilation Guide

Balanced Intake & Exhaust Per IRC Code

This guide explains how to design balanced attic ventilation per IRC code. Total NFA must equal 1 sq ft per 150 sq ft of attic floor (or 1:300 with vapor barrier), split 50/50 between low intake (soffit vents) and high exhaust (ridge or gable vents). Mixing exhaust types (ridge + gable) short-circuits the system and is a common mistake. Topics include ridge vent vs box vent, soffit vent sizing, and how to retrofit an existing attic. Pair with our Vents Calculator.