Everything homeowners need to know about building an accessory dwelling unit in Fort Collins - size limits, setbacks, permits, and how a contentious local rewrite and Colorado's statewide ADU law together reshaped the city's rules.
Last verified: August 2026
7/10 · ADU-friendly
1,000 sq ft*
Max ADU size
No taller than home
Max height
Not required
Owner-occupancy
By-right
Permit type
This page summarizes the Fort Collins Land Use Code's Accessory Dwelling Unit standards, as amended by Ordinance No. 009, 2025 to align with Colorado's statewide ADU law (HB 24-1152), for general reference - it is not legal advice. Regulations change; always confirm current requirements with the Fort Collins Development Review Center before designing or applying for permits. See sources below.
Zoning & size requirements
What you're allowed to build
ADU type
Max size
Max height
Notes
Detached (new build)
750 sq ft if the primary home is 1,667 sq ft or smaller; 1,000 sq ft or 45% of the primary dwelling's floor area (whichever is less) if the primary home is larger. Converting an existing legal accessory structure is capped at 800 sq ft
Cannot exceed the height of the primary dwelling on the same lot
Must sit behind the primary dwelling; a minimum 5 ft separation from other buildings applies, with additional setbacks that vary by zone district
Attached (addition or basement conversion)
At or above grade: the greater of 750 sq ft or 45% of the primary dwelling. Basement level: the greater of 750 sq ft or 100% of that floor
Same as the primary structure
Common approach for a basement conversion or above-grade addition
Allowed zoning districts
Following Ordinance No. 009, 2025 (effective February 14, 2025), ADUs are allowed by right in every zone district where a single-unit dwelling is permitted or exists - including Old Town's OT-A, OT-B, and OT-C subdistricts, which previously had narrower rules. Confirm your parcel's zoning with the Fort Collins Development Review Center.
Additional standards
Setbacks, parking & other rules
Setbacks
Detached ADUs must sit behind the primary dwelling with at least 5 ft separation from other buildings; specific front, side, and rear setbacks vary by zone district
Parking
No additional off-street parking is required specifically for the ADU - Ordinance 009, 2025 eliminated ADU parking requirements citywide, ahead of Colorado's statewide parking-mandate ban
Units per lot
1 ADU permitted per detached house (or, in most zones, per duplex or triplex), in addition to the primary dwelling
Owner-occupancy
Not required, consistent with Colorado's HB 24-1152. Fort Collins does not impose its own owner-occupancy condition on ADUs
Building code
Must meet Fort Collins' adopted residential building code dwelling-unit standards
Rental license
Long-term rentals (30+ days) are allowed for both the ADU and the primary home. Short-term rental use is barred for any ADU that received a building permit on or after January 1, 2024 (Fort Collins Municipal Code §15-646)
Ordinance history
How Fort Collins's ADU rules got here
2022Sweeping Land Use Code rewrite adopted. On November 1, 2022, City Council voted 5-2 to adopt the city's first major Land Use Code update since 1997, which included by-right ADUs as part of a broader set of density reforms.
2023Code repealed after resident backlash. A petition drive by the group Preserve Fort Collins forced Council to choose between repealing the new code or sending it to a public vote. In January 2023, Council voted 7-0 to repeal it, and the November 2022 reforms - including their ADU provisions - never took effect.
2023A revised, narrower code passes instead. On October 17, 2023, Council adopted a scaled-back Land Use Code 5-1, again legalizing ADUs in residential zones including the Low Density Residential (RL) district.
2024Colorado passes HB 24-1152. The statewide ADU law required "subject jurisdictions" like Fort Collins, a member of the North Front Range Metropolitan Planning Organization (NFRMPO), to allow at least one ADU by right in every zone permitting a single-unit dwelling by June 30, 2025.
2025Ordinance 009, 2025 aligns the city with state law. Adopted February 4, 2025 and effective February 14, 2025, it extended by-right ADU eligibility to every zone allowing a single-unit dwelling (including Old Town), moved ADU review to an administrative-only Basic Development Review with no appeal, and eliminated ADU parking requirements citywide.
Fort Collins, home to Colorado State University, has a long history of contentious housing politics - the city's "U+2" ordinance limiting unrelated roommates to three per household dated to 1964 and wasn't repealed until Colorado's 2024 occupancy-limit ban forced the issue. ADUs followed a similar arc: proposed reforms were rejected once by petition before finally passing in a narrower form. Fort Collins is now a certified Colorado "ADU Supportive Jurisdiction," but the city's development fees, not its zoning, are the more likely hurdle for homeowners today.
Permit process
How Fort Collins ADU permitting works
1
Confirm your zone and review track
ADUs are allowed in every zone that permits a single-unit dwelling; most projects go through Basic Development Review (BDR), an administrative process with no public hearing.
2
Plan your utility connections early
Decide whether the ADU will share a water and sewer tap with the primary home (assessed by fixture count) or need its own - utility Plant Investment Fees are one of the largest cost drivers.
3
Prepare your plan set
Site plan, floor plans, and elevations, plus the size calculation showing compliance with the 750/1,000 sq ft-or-45% formula.
4
Optional conceptual review
Meet informally with city staff for feedback before you submit formally - there's no fee for this step.
5
Basic Development Review
Submit through the city's online portal and pay the flat BDR fee. The Development Review Manager or Community Development and Neighborhood Services Director decides; there's no public hearing and no appeal for ADU applications.
6
Building permit & inspections
Once BDR is approved, pull your building permit and complete the standard framing, plumbing, electrical, and final inspections.
Fees and utility charges change periodically - confirm current figures with the Fort Collins Development Review Center before budgeting your project.
Budgeting
What it costs to build an ADU in Fort Collins
Garage conversion
Roughly $90,000-$180,000, the least expensive path since the shell already exists
Basement conversion
Roughly $120,000-$230,000, depending on existing ceiling height and utility access
New detached ADU
Roughly $170,000-$380,000+ for a code-compliant, fully insulated freestanding unit
Basic Development Review fee
A flat fee, commonly cited around $6,925, separate from the building permit fee
Utility Plant Investment Fees (PIFs)
Often $5,000-$15,000 for an ADU sharing utilities with the primary home, assessed by fixture count; a full new 3/4" tap runs roughly $27,000 after 2026 increases. Combined with BDR and permit fees, total city development fees commonly land around $20,000-$25,000
These are general ranges from local contractor estimates and regional reporting, not quotes - actual cost depends heavily on lot conditions, finishes, and utility connections. Fort Collins' development fees are notably higher than several peer Colorado and Pacific Northwest cities, even though its zoning process itself is now fully administrative.
Before you apply
Tips for a smooth approval
Check your primary home's size before assuming your ADU cap. The 750 sq ft vs. 1,000 sq ft / 45% formula turns on whether your house is above or below 1,667 sq ft - confirm the number for your lot before designing.
Budget for utility fees separately from construction. Plant Investment Fees are billed apart from the Basic Development Review and building permit fees, and 2026 increases have made them a bigger share of total cost.
Use the free conceptual review. Getting informal staff feedback before you submit formally can catch zone-specific setback or design issues early, when they're cheap to fix.
Know that ADU decisions can't be appealed. Basic Development Review is fast, but that also means there's no formal appeal step if a decision doesn't go your way - get your application right the first time.
Decide on short-term rental plans before you apply. Any ADU permitted on or after January 1, 2024 is barred from short-term rental use, so plan for long-term rental if that's a consideration.
FAQ
Common questions
Do I need to live on the property to build an ADU in Fort Collins?
No. Colorado's HB 24-1152 bars cities from requiring owner-occupancy for ADUs, and Fort Collins does not impose its own version of that requirement.
How many ADUs can I build on one lot in Fort Collins?
One ADU is permitted per detached house (or, in most zones, per duplex or triplex), in addition to the primary dwelling.
Do I need extra parking for an ADU?
No. Ordinance 009, 2025 eliminated ADU parking requirements citywide, ahead of Colorado's statewide ban on most ADU parking mandates.
What's the maximum size for a detached ADU in Fort Collins?
750 sq ft if your primary home is 1,667 sq ft or smaller, or 1,000 sq ft (or 45% of the primary home's floor area, whichever is less) if it's larger. A detached ADU also can't exceed the height of the primary dwelling.
How long does the permit process take?
Most ADUs go through Basic Development Review, an administrative process with no public hearing - generally faster than a discretionary review, though exact timelines depend on application completeness. Confirm current timelines with the Development Review Center.
How much does an ADU cost to build in Fort Collins?
Garage conversions run roughly $90,000-$180,000, basement conversions roughly $120,000-$230,000, and new detached units roughly $170,000-$380,000+, based on local contractor estimates and regional reporting - not counting the roughly $20,000-$25,000 in typical city development fees.
Why did Fort Collins' Land Use Code change twice in such a short period?
A sweeping code rewrite adopted in November 2022 - which included by-right ADUs - was repealed in January 2023 after a citizen petition drive. Council then passed a narrower revised code in October 2023, which was later updated again by Ordinance 009, 2025 to fully comply with Colorado's statewide ADU law.
Are Fort Collins' ADU development fees really higher than other Colorado cities?
Based on published fee schedules, yes - Fort Collins' combined Basic Development Review and utility Plant Investment Fees commonly total $20,000-$25,000, noticeably more than the roughly $5,000-$8,000 in typical city fees reported for Denver.
Can I rent my ADU out on Airbnb or a short-term rental platform?
Not if it was permitted on or after January 1, 2024 - Fort Collins bars short-term rental use for those units under Municipal Code §15-646. Long-term rentals of 30 days or more are allowed.
