Tempe, AZ Environmental Rules: Flood Elevation Requirements (2026)

Section 12-18 of the general code defines 'Regulatory Flood-Elevation (RFE)' as an elevation one foot above the base flood elevation FEMA computes for a one-percent-annual-chance flood, so Tempe's standard runs a foot of freeboard above the federal minimum. Section 12-29(3) applies that standard by use type. Residential new construction or substantial improvement must have its lowest floor, including any basement, elevated to or above the RFE; in an AO zone without a published depth number, the floor must sit at least two feet above the highest adjacent grade, and in an unmapped A zone the Floodplain Administrator must pull the best available base flood data from FEMA or the state before applying the RFE.

Non-residential buildings may either meet the same elevation or be floodproofed watertight below the RFE with structural components able to resist hydrostatic and hydrodynamic loads, under § 12-29(3)(b). Section 12-29(3)(c) adds flood-opening requirements for enclosed areas below the lowest floor used only for parking, access, or storage: at least two openings on different walls, one square inch of net opening area for every square foot of enclosed floor space, with the lowest opening no higher than one foot above grade. On completion, § 12-29 requires a registered professional engineer or surveyor to certify the as-built lowest-floor elevation, and Tempe's building inspector verifies it before the Floodplain Administrator signs off.

Detached garages and small storage accessory structures can be built below the RFE only if constructed with flood-resistant materials, anchored against flotation, and designed to admit floodwater automatically per § 12-29(3)(f).