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

Lynwood Municipal Code Section 15-14 sets the construction standards that apply throughout the city's mapped special flood hazard areas. Under subsection c1, new construction and substantial improvements must have the lowest floor, including any basement, elevated to or above the base flood elevation, the water-surface height reached by the flood having a one percent annual chance of occurring (the '100-year flood,' defined in Section 15-5). Nonresidential structures may instead meet the floodproofing alternative in subsection c3, making the structure watertight below the base flood level with walls substantially impermeable to water and components able to resist hydrostatic and hydrodynamic loads, certified by a registered engineer or architect.

In Zone AR, AR/AH, or AR/AO, subsection c2 requires the lowest floor elevated above the highest adjacent grade to at least the depth number shown on the FIRM, or at least two feet if the FIRM lists no depth number. Whichever standard applies, the finished elevation must be certified by a registered professional engineer or surveyor, or verified by the city's building inspector, and that certification goes to the Floodplain Administrator. Subsection c4 additionally requires enclosed areas below the lowest floor that can flood to have at least two openings with a combined net area of one square inch per square foot of enclosed space, with opening bottoms no higher than one foot above grade, so floodwater can enter and exit and equalize hydrostatic pressure on the walls.