Roof Ventilation Calculator

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Ventilation Requirements

Enter attic dimensions and vent type preferences

Attic Length (ft)

Attic Width (ft)

Ventilation Rule

Exhaust Vent Type

Intake Vent Type

How Roof Ventilation Works

Proper attic ventilation requires a balanced system of intake vents (at the eaves/soffits) and exhaust vents (at or near the ridge). The IRC building code requires:

Total NFA Required = Attic Floor Area ÷ Ventilation Ratio
1/300 rule: 1 sq ft NFA per 300 sq ft attic (with balanced vents)
1/150 rule: 1 sq ft NFA per 150 sq ft attic (without vapor barrier)
NFA = Net Free Area (actual open airflow area)

NFA (Net Free Area) is the actual open area of a vent after accounting for screens and louvers. A vent's NFA is typically 50-60% of its physical size.

Balanced Ventilation (50/50 Rule)

50% of total NFA should be intake (soffit vents)
50% of total NFA should be exhaust (ridge/box vents)
Slightly more intake than exhaust is acceptable (60/40)

📊 Ventilation Plan

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Enter attic dimensions to calculate ventilation needs.

Ventilation Requirements

How Roof Ventilation Works

Balanced Ventilation (50/50 Rule)

Cost Calculator

Square Footage

Roof Load

📊 Ventilation Plan

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