A.Lynn Underwood, an engineer, licensed contractor, and building code official in Norfolk, Va., responds: If a basement measures less than 200 square feet and is used only for mechanical equipment, no windows are required by the IRC, though foundation ventilation, crawlspace access, and flood vents may be needed. Otherwise, all basements with full-height foundation walls must have at least one emergency egress window. Local codes may require additional fenestration for natural lighting and ventilation.

But even if you intend for the basement to be nonhabitable, installing full-height precast foundation walls could allow for conversion to living space later on, in which case section R310 of the 2006 IRC requires that every sleeping area have an emergency egress opening, with a sill that isn’t any higher than 44 inches above the floor. While the...

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