Static/Passive Venting

Static - Passive Attic Ventilation

Passive attic ventilation is just heat escaping the attic space without the aid of mechanical or wind induced low pressure. Hot air rises and is replaced by cooler air. The attic space is warmed by either warm air escaping the heated living area, and/or by the sun and heat radiating through the roofing. This heat will naturally rise to the top of the attic and escape through any open holes or vents in the roof.

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Attic Fan | Cooling a hot attic space

Testing the effectiveness of a powered attic fan versus ridge vent and soffit ventilation.

Myth - A power roof ventilator will pull air from your roof ridge vent and short circuit the air flow from the lower eave soffit vents.

Fact - A powered roof fan will cool your hot attic space faster and more efficiently than ridge vent and soffit vents alone without compromising the venting system.

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Real World Attic Ventilation

Attic and roof ventilation in the real world. How it works.

The pretty pictures and diagrams you see on the ventilation manufacturers websites are a far cry from everyday construction reality.

For instance, below is a photo taken in the middle of winter after a winter storm. About 12 inches of snow have have fallen in the past 4 days in this area. The roof is a hip style on a contemporary home near Cleveland, Ohio. The roofing material is Ludowici round butt Lanai flat tile with a weathered texture. The house is about 70 years old and has had annual ice dams in winter caused by poor insulation and inadequate attic / roof ventilation.

The interesting thing in this photo is how it shows what really happens when ridge vents are mixed with static (mushroom, turtle, etc.) vents on a roof for attic ventilation.

According to many roof ventilation manufacturers websites, the static vents should be removed to prevent a "short circuiting" of the ventilation airflow.

As seen below, heat is coming out of the attic from both the lower static vents and the ridge vent. The ridge vent here is a custom installation consisting of ventilation material over a hole cut in the ridge roof boards which was then covered by the roof tile.

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A Roof Venting Analogy

A simple, and wrong, roof venting analogy often used as an example when trying to support the reasoning for closing off roof vents when installing ridge vents

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Attic / Roof Ventilation | Smoke Test

Large attic smoke test.

Exterior temperature :  80 deg. F

Interior temperature

     Attic floor :  95 deg. F

     Attic peak :  109 deg. F

Sunny with a light breeze off Lake Erie.

Red slate roof.

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