Boulder County, CO Environmental Rules: Flood Zones (2026)

Boulder County's regulatory floodplain is established as the Floodplain Overlay District in the Boulder County Land Use Code Article 4-400. The district consists of FEMA Special Flood Hazard Areas shown on the current Flood Insurance Rate Maps (FIRMs) and additional county-adopted floodplain mapping for Boulder Creek, the St. Vrain, Left Hand Creek, and other regulated waterways. Any construction, fill, grading, or substantial improvement within the district requires a Floodplain Development Permit (FDP) from the Floodplain Administrator (303-441-3930, floodplainadmin@bouldercounty.gov), in addition to any building permit. Boulder County participates in the NFIP since 1974, allowing residents to purchase federally backed flood insurance, and as a CRS Class 5 community provides a 25% premium discount on NFIP policies in unincorporated areas regardless of flood zone. Following the September 2013 flood that overwhelmed Boulder Creek, the St. Vrain, and Left Hand Creek, the Board of County Commissioners updated FIRMs (FEMA approval 2012 and subsequent revisions) and adopted DC-22-0004 (Resolution 2023-036, May 11, 2023) amending Article 4-400 and Article 4-802 to align with current FEMA and Colorado Water Conservation Board (CWCB) standards. New residential structures in the floodplain must elevate the lowest floor above the regulatory base flood elevation per the LUC, and substantial improvements (work valued at 50% or more of the structure's market value over a rolling period) trigger full floodplain compliance. Properties outside mapped floodplains can still flood; FEMA flood insurance is available to any property owner in a participating community.