Broomfield, CO Environmental Rules: Flood Elevation Requirements (2026)

Section 17-40-160 sets the specific construction standards that apply once base flood elevation data exists for a site, whether from the city's FEMA-based Flood Insurance Rate Map or data the city engineer develops under section 17-40-130. Subsection (A) requires new construction and any substantial improvement of a residential structure, meaning work costing 50% or more of the structure's pre-improvement market value, to have its lowest floor, including any basement, elevated to at least one foot above the base flood elevation. Subsection (B) gives nonresidential buildings, commercial, industrial, or otherwise, a choice: elevate the lowest floor that same one foot above base flood elevation, or floodproof the structure below that same one-foot mark so the walls are watertight and impermeable, with structural components able to resist hydrostatic and hydrodynamic loads.

A floodproofing design must be certified to the city engineer by a registered professional engineer or architect under subsection (B)(3). Subsection (C) requires enclosed areas below the elevated lowest floor to have automatic flood vents, at least two openings totaling one square inch per square foot of enclosed area, with the lowest opening no higher than one foot above grade, so hydrostatic pressure equalizes rather than damaging the walls. Manufactured homes face the same one-foot freeboard under subsection (D), anchored to resist flotation and lateral movement, and recreational vehicles are exempt only if they stay fewer than 180 consecutive days, are licensed and ready for highway use, or meet the same elevation and anchoring standards.

Properties raised out of the floodplain by a FEMA Letter of Map Revision based on Fill still owe the same one-foot elevation above the pre-fill base flood elevation under section 17-40-150(D).