ADU Rules in Fort Collins, Colorado

Fort Collins allows accessory dwelling units under its Land Use Code and updated its local rules to align with Colorado's 2024 ADU legislation. The exact design envelope depends on the existing primary building, the type of ADU, and the underlying zone district.

Detached ADU Size

For a new detached ADU, the current standards use a tiered maximum:

• If the primary building is under 1,335 sq ft, the detached ADU is limited to 600 sq ft.
• If the primary building is 1,335 sq ft or larger, the detached ADU may be up to 1,000 sq ft or 45% of the primary dwelling's floor area, whichever is less.
• Conversions or additions involving an existing legal accessory structure have separate limits and should be checked against the current Land Use Code.

These rules replace the older blanket “800 sq ft” or “1,000 sq ft / 50%” summaries that appeared on this page.

Height and Separation

A detached ADU is generally limited to 1.5 stories / 28 ft, or a lower limit if the underlying zone district requires one. A detached ADU must also maintain the required separation from the primary dwelling and comply with the applicable zone-district setbacks.

Do not use a universal 5 ft side/rear setback for every Fort Collins parcel. The current standards tie those setbacks to the applicable zone district and site conditions.

Owner Occupancy and Parking

Fort Collins amended its ADU rules to comply with Colorado HB24-1152. The state-aligned framework does not allow a local owner-occupancy requirement as a condition of ADU approval. Parking should be checked against the current local code for the property and application type rather than relying on older blanket statements.

Permit Process

1. Confirm that an ADU is allowed on the lot and identify the underlying zone district.
2. Determine whether the proposal is a new detached ADU, attached/internal ADU, or conversion of an existing legal accessory structure.
3. Check the applicable floor-area, height, separation, setback, utility, and building-code requirements.
4. Submit the required development-review and building-permit materials through the City's current application system.
5. Complete required inspections before occupancy.

Current applications show Fort Collins processing ADUs through its normal development-review system, but review time varies by project and corrections; this page therefore does not give a fixed “4–6 week” promise.

Official Sources

Use the current Fort Collins Land Use Code and the City's Development Review resources for the parcel-specific rules. Colorado HB24-1152 provides the state framework that Fort Collins implemented locally.

Fort Collins Development Review
281 N. College Ave, Fort Collins, CO 80524
Website: fcgov.com/developmentreview

Disclaimer: This guide is a summary for orientation. Confirm the current Land Use Code, zoning, and permit requirements for the specific property before designing or building an ADU.