Roofing
Soffit
The underside of the roof overhang (eave), typically finished with vented panels to allow air into the attic and prevent moisture buildup.
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In the Field
Soffit vents are the intake side of the attic ventilation system — ridge vents are the exhaust. Block a soffit vent with insulation and you create a moisture trap. Always maintain a clear air channel from soffit to ridge through baffles when insulating the attic floor.
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Rule of Thumb
IRC requires 1 square foot of net free ventilation area for every 150 square feet of attic floor space (1:150), reducible to 1:300 with a vapor barrier and balanced intake/exhaust.