"Understanding Your Home" by Building Inspector Mark Visser
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Ridge vent for flat roofs


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Ventilation for Flat Roofs...
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Flat roof ventilation. Ridge vent for flat roofs. Siffit vent.

When there is no insulation in a roof cavity, warm air circulation inside absorbs condensed moisture and keeps the roof and ceiling relatively dry.
The temperature of the entire roof structure is high enough that a condensation problem is not likely to develop.
Insulation above the ceiling in the roof will reduce heat loss but will not completely eliminate air leakage. Warm, moist air can still leak into the cool, insulated roof space from living areas and condense.
Since most flat or compact roofs usually have ineffective ventilation , this condensation could get trapped within the insulation.
50% Of the required ventilation should be provided by a continuous soffit vent and 50% through a continuous ridge vent.
The air can freely flow through the continuous vent, over the joists, and over the ridge vent. Failure to provide adequate ventilation may cause deterioration of the roof structure.
To the left is an illustration of a continuous ridge vent on a built-up curb.




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