What Is Roof Ventilation?
Roof ventilation is the paired system of intake vents (usually at the soffits) and exhaust vents (ridge, box, or powered vents) that moves air through the attic. The common design guideline is roughly one square foot of net free vent area per 150 square feet of attic floor, split about evenly between intake and exhaust; many codes allow 1:300 when a balanced system or vapor barrier is present. In Central Texas heat, attic temperatures can exceed 150 degrees F, and inadequate ventilation cooks asphalt shingles from below, ages them prematurely, and can void manufacturer warranties. The most common defect is a good ridge vent starved by blocked or undersized soffit intake. Both under-ventilation and over-ventilation (mixing exhaust types that short-circuit airflow) cause problems. Ventilation is evaluated during any competent roof inspection and is a frequent code-upgrade item on Austin-area replacements.
Also Known As
These are the search terms and phrases that commonly refer to this topic, so you can find it however you describe it.
How Roof Ventilation Relates to Other Topics
Mixing exhaust types - a ridge vent plus a powered fan, or ridge plus box vents - short-circuits the system: the stronger exhaust pulls its air from the weaker one instead of from the soffits, and the attic below stays unvented.
Ventilation is sized in net free area, and the rule is intake-heavy: when exhaust exceeds soffit intake, part of the ridge vent becomes intake, pulling weather in at the exact line the system was supposed to push air out.
Ventilation is the cheapest energy upgrade on a roof: clearing blocked soffits or balancing exhaust costs a fraction of a reflective roof and attacks the same attic heat load the expensive options do.
Questions about Roof Ventilation?
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