Accessory Structures in Fort Collins, CO

Fort Collins maintains 166 local ordinances across all categories, and 5 of those deal specifically with accessory structures. Here is a breakdown of what the city actually requires, what is prohibited, and where Fort Collins falls on the strict-to-permissive spectrum compared to other cities.

Tiny Homes

Fort Collins has formally adopted Appendix BB Tiny Houses of the International Residential Code in full, giving tiny homes on foundations their own building-code path rather than forcing them to meet standard single-family dwelling rules.

Key details: Adoption: IRC Appendix BB adopted in its entirety. Related appendix: Appendix BC ADUs, amended locally. ADU cap: One ADU per lot. Adopting ordinance: City Code Sec. 5-30. Enforcing agency: CDNS.

Constructing a tiny house that does not meet Appendix BB's adopted construction standards, or siting one as an ADU without following the amended Appendix BC conditions such as the one-ADU-per-lot cap, is enforced by CDNS through permit denial or a stop-work order; occupancy can be withheld until the structure or its ADU status is brought into compliance.

ADU Rental Restrictions

Fort Collins allows only one extra kitchen inside a single-family dwelling, and only through a minor amendment approval under Transitional Land Use Code Section 3.5.2(H). Before a building permit issues, the owner must record a notarized affidavit with Larimer County confirming the second kitchen will never be used to create a separate rental or second dwelling unit.

Key details: Max additional kitchens: 1 per dwelling unit. Approval required: Director minor amendment, § 2.2.10. Recorded document: Notarized affidavit, Larimer County Recorder. Kitchen location ban: Not allowed in accessory buildings. Access rule: No locked doors between kitchens.

Building or using a second kitchen without Director approval, or converting an approved second kitchen into a separate dwelling in violation of the recorded affidavit, is a Land Use Code violation. Under Section 2.14.4(A), violators are guilty of a misdemeanor subject to the penalties in City Code Section 1-15, with each day of a continuing violation counted as a separate offense; the City can also withhold or revoke building permits tied to the unauthorized unit.

Compared to other cities, Fort Collins takes a harder line on adu rental restrictions. The enforcement and penalty structure reflects that.

ADU Rules

Fort Collins caps every lot at one accessory dwelling unit under City Code § 5-30's adoption of 2024 IRC Appendix BC. An ADU must sit inside an existing single-family detached home or townhouse, carry its own house number, stay secondary in size and function to the main dwelling, and meet the city's Land Use Code.

Key details: Governing rule: City Code § 5-30, 2024 IRC Appendix BC101.2. ADUs per lot: One maximum. Eligible host structure: Existing single-family or townhouse dwelling. Detached ADU siting: Must comply with IRC § R302.7. Addressing: Separate house number required.

An ADU that fails any BC101.2 condition, a second unit on the same lot, one without its own house number, or a detached unit sited without regard to IRC Section R302.7, is a building code violation. The code official can deny or revoke the building permit, require correction of the work, or issue a stop-work order until the unit satisfies all six conditions, including the one-ADU-per-lot cap and the Land Use Code's separate zoning requirements.

ADU Impact Fees

Fort Collins charges capital expansion impact fees on accessory dwelling units before a building permit issues, billed on a discounted "Multifamily/ADU" square-footage tier under City Code Chapter 7.5. The community parkland fee alone runs $1,611 to $2,494 per ADU depending on size, on top of separate police, fire, and other capital expansion fees.

Key details: Governing chapter: Municipal Code Ch. 7.5, Capital Expansion Fees. Parkland fee, ADU under 750 sf: $1,611 (as of 1/1/2026). Parkland fee, ADU over 1,301 sf: $2,494 (as of 1/1/2026). Police fee, ADU tier: $375 to $567 per unit. When fee is due: Before building permit issuance.

Building permits for an ADU are not issued until the Chapter 7.5 fees are paid to the City; nonpayment simply blocks permit issuance rather than triggering a separate fine. A refund of an overpaid or unspent fee must be requested from the Financial Officer within 180 days after the ten-year expenditure deadline under Sec. 7.5-24(c), and the City retains an additional 2 percent of any refunded amount to cover administrative costs. Knowingly making a false statement to obtain a Sec. 7.5-26 affordable-housing fee deferral is itself a violation of that section.

Shed & Carport Rules

Fort Collins exempts small storage sheds from a building permit only if the shed is one story, 120 square feet or less, no taller than 8 feet, holds no more than 10 gallons of flammable liquid, and sits at least 3 feet from the property line.

Key details: Permit-exempt shed max area: 120 square feet. Permit-exempt shed max height: 8 feet. Minimum setback for exempt shed: 3 feet from property line. Flammable liquid limit: 10 gallons per building. Applies under: 2024 IBC/IRC Sec. 105.2/R105.2 as amended.

Building or enlarging an accessory structure beyond the 120-square-foot, 8-foot, or 3-foot exemption thresholds without first obtaining a building permit is a code violation enforceable by the Building Services division; the code official can issue a stop-work order and require the owner to obtain a permit retroactively, with fees and possible penalties under the City's general building-code enforcement provisions.

The Bottom Line

Fort Collins's accessory structures rules are a mixed bag. Some areas are strict, others are relaxed, and the details matter. The best approach is to check the specific rule that applies to your situation rather than assuming Fort Collins is broadly strict or permissive.

This guide is based on Fort Collins's current municipal code. Local rules can and do change, so check the individual ordinance pages for the latest details, penalties, and FAQs.