Solano County, CA Environmental Rules: Flood Elevation Requirements (2026)

2-50 of the Flood Damage Prevention Ordinance sets Solano County's construction standards inside mapped special flood hazard areas, and its freeboard requirement is one of the most consequential numbers in the chapter. Under subsection (c)(1), new construction and substantial improvement of any residential structure must have its lowest floor, including any basement, elevated at least one foot above the base flood elevation (BFE), the water-surface elevation FEMA's Flood Insurance Rate Map shows for a flood with a 1-percent annual chance of being equaled or exceeded.

Once built, that elevation must be certified by a registered professional engineer or land surveyor, or verified by the county building inspector, with the certification delivered to the floodplain administrator. In Zones AO or VO, where the FIRM shows a flood depth rather than a fixed elevation, subsection (c)(2) instead requires the lowest floor to sit at least one foot above the highest adjacent grade plus the mapped depth number, or three feet above grade if no depth number is shown. Subsection (b)(2) extends the same one-foot buffer to electrical, heating, ventilation, air-conditioning, plumbing, and duct equipment, unless it is specifically designed and installed to resist flood forces and keep water out.

Nonresidential structures may meet the same elevation standard or, under subsection (c)(3), be dry floodproofed with watertight walls and structural components engineered to resist hydrostatic and hydrodynamic loads, certified by a registered civil engineer or architect. Enclosed areas below the lowest floor used only for parking, access, or storage must include flood vents, at least two openings on different walls totaling one square inch of net area per square foot of enclosed space, with the lowest opening no higher than one foot above grade.