Tigard, OR Environmental Rules: Flood Elevation Requirements (2026)

Section 9.10.050 of the Tigard Municipal Code sets the elevation standards for the City of Tigard's mapped flood zones. In riverine areas with base flood elevations, Zones A1-A30, AH and AE, subsection M.2 requires new construction, conversion to, and substantial improvement of any residential structure to have the lowest floor, including basement, elevated at one foot above the base flood elevation. Subsection M.3 applies the same one foot height to commercial, industrial and other nonresidential structures, but allows the owner to floodproof instead so the structure is watertight below the base flood level, with structural components that resist hydrostatic and hydrodynamic loads and buoyancy, certified by a registered professional engineer or architect. Base flood elevation means the elevation to which floodwater is anticipated to rise during the base flood, which has a one percent chance of being equaled or exceeded in any given year.

Other zones and structures have their own heights. Where no base flood elevation data is available in a riverine unnumbered A Zone, § 9.10.050.J requires a minimum of two feet above the highest adjacent grade. In AO Zones, residential lowest floors must be elevated to or above the depth number on the Flood Insurance Rate Maps, or at least two feet if no depth number is specified. Manufactured dwellings need the bottom of the longitudinal chassis frame beam at or above base flood elevation, with electrical crossover connections a minimum of 12 inches above it. New critical facilities allowed in a flood hazard area must have the lowest floor elevated three feet above base flood elevation or to the height of the 500-year flood, whichever is higher. Electrical, heating, plumbing and similar equipment must be elevated at or above the base flood level or protected from water entry.

Elevation is verified in § 9.10.040.D: the lowest floor elevation is certified by a licensed surveyor or engineer once the lowest floor is placed and before further vertical construction, and a record drawing certification is required before final inspection. Subdivisions of more than 50 lots or five acres must include base flood elevation data.