CSLB C-39 Roofing ContractorFlashing, Ventilation and InsulationEasy
A roofing contractor is designing a balanced attic ventilation system using both soffit (intake) and ridge (exhaust) vents. To prevent airflow short-circuiting and ensure the attic ventilates properly, how should the total required net free ventilating area generally be distributed?
- A75% at the gable ends and 25% at the ridge
- B100% at the soffits with no ridge exhaust needed
- C90% at the ridge and 10% at the soffits
- DApproximately 50% at the soffits (intake) and 50% at the ridge (exhaust)
Show answer & explanationAnswer & explanation
Correct answer: D. Approximately 50% at the soffits (intake) and 50% at the ridge (exhaust)
Balanced ventilation relies on roughly equal intake (low, at soffits) and exhaust (high, at ridge) net free area so air flows continuously from eave to ridge, sweeping the entire underside of the roof deck. An imbalance causes dead air pockets and reduces the system's cooling and moisture-control effectiveness.
Why the other options are wrong
- A. Gable vents at 75% can short-circuit airflow and bypass much of the roof deck.
- B. Without exhaust, hot/moist air cannot escape at the ridge.
- C. Too little intake starves the exhaust vents of makeup air.
Balanced Ventilation Distribution
Attic ventilation systems perform best when intake (soffit) and exhaust (ridge) net free areas are roughly equal, promoting continuous low-to-high airflow.
- Intake at eaves/soffits, exhaust at ridge
- Roughly 50/50 split prevents dead zones
- Imbalance reduces cooling and moisture control
Memory trick: Half in, half out keeps the attic breathing throughout.