How attic ventilation works — cool air in at the soffits, hot air out at the ridge

A vented attic is a chimney: cool air enters low at the soffits, sweeps the underside of the deck, and leaves hot at the ridge. It only works when intake (low) and exhaust (high) net free areas are balanced ~50/50.

Cross-section of a vented attic showing the airflow path. Cool outside air enters low through continuous soffit (eave) vents, washes up the underside of the roof deck along both slopes, and hot, moist air rises out the top through a continuous ridge vent. Insulation covers the attic floor with a one-inch clear airspace kept open at each eave by a baffle. The system is balanced when the intake net free area at the soffits equals the exhaust net free area at the ridge — about half low and half high. — Source: 2021 IRC R806.2 / R806.3 · HVI intake–exhaust balance

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Cross-section of a vented attic showing the airflow path. Cool outside air enters low through continuous soffit (eave) vents, washes up the underside of the roof deck along both slopes, and hot, moist air rises out the top through a continuous ridge vent. Insulation covers the attic floor with a one-inch clear airspace kept open at each eave by a baffle. The system is balanced when the intake net free area at the soffits equals the exhaust net free area at the ridge — about half low and half high.

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    <img src="https://remodelcalculators.com/api/figure-embed/attic-ventilation-airflow" alt="Cross-section of a vented attic showing the airflow path. Cool outside air enters low through continuous soffit (eave) vents, washes up the underside of the roof deck along both slopes, and hot, moist air rises out the top through a continuous ridge vent. Insulation covers the attic floor with a one-inch clear airspace kept open at each eave by a baffle. The system is balanced when the intake net free area at the soffits equals the exhaust net free area at the ridge — about half low and half high." width="800" height="480" style="width:100%;height:auto;border:0" loading="lazy">
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