Larimer County, CO Accessory Structures: ADU Rules (2026)

Larimer County uses the term 'Accessory Living Area' (ALA) for what other jurisdictions call ADUs. ALAs are governed by the Larimer County Land Use Code (Article 4) and adopted building codes. Colorado HB24-1152, codified at C.R.S. 29-32-101 et seq., took effect June 30, 2025 and preempts ADU regulation in 'subject jurisdictions' - municipalities of 1,000+ within a Metropolitan Planning Organization, plus county areas inside census-designated places of 40,000+ within an MPO. Because the unincorporated Fort Collins-area census-designated places fall under HB24-1152, Larimer County removed the separate planning-process requirement so applicants now apply directly for a building permit. One ALA is permitted per lot. Total square footage must comply with Land Use Code Table 3-15 (size scales with primary dwelling and zone district). One additional off-street parking space is required for the ALA. The ALA must have at least one exit directly to the exterior that does not lead into a garage or barn. Because most of unincorporated Larimer County exceeds International Residential Code prescriptive wind and snow load limits, structural plans must be drawn and stamped by a Colorado-licensed Professional Engineer. New ALA dwelling units also require a radon mitigation system, radon testing, and prewiring for solar PV and EV charging where applicable. Permits go through Larimer County Community Development at 200 W. Oak St., Fort Collins (970-498-7700). Owner-occupancy demonstration may be required at the time of application but no permanent commitment or deed restriction may be imposed on subject jurisdictions under HB24-1152.