Brentwood, CA Environmental Rules: Flood Elevation Requirements (2026)

300(C), part of the city's floodplain management chapter, sets construction elevation standards for all areas of special flood hazard. For AO zones, the lowest floor including any basement must be elevated above the highest adjacent grade to a height equal to or exceeding the depth number shown on the Flood Insurance Rate Map, or at least four feet above the highest adjacent grade if no depth number is specified. 220(b). For every other flood zone, the freeboard requirement doubles: the lowest floor must be elevated to two feet above the base flood elevation.

Once built, a registered professional engineer or surveyor must certify the lowest floor's elevation, and the city's community building inspector must verify it before that certification goes to the floodplain administrator. Nonresidential construction can instead be flood-proofed watertight below the same elevation, with structural components certified to resist hydrostatic and hydrodynamic loads. Enclosed areas below the lowest floor used only for parking, access or storage must have flood vents sized to at least one square inch of opening per square foot of enclosed area, with the bottom of openings no higher than one foot above grade, so floodwater can enter and exit automatically rather than pushing on the walls.