Building an ADU in Fort Collins
City code and Colorado law · Last reviewed October 9, 2026
Since February 2025, Fort Collins allows an accessory dwelling unit (ADU) in all zone districts on a lot with a house, duplex or triplex, as long as the property meets city requirements. A detached ADU can be 750 square feet behind a home under 1,667 square feet, or up to 1,000 square feet (45% of the home) behind a larger one. Every ADU goes through a Basic Development Review with a $6,925 flat fee and then a building permit; the city says total fees may run $20,000 to $25,000. [1]
| Where allowed | All zone districts, on a lot with (or allowed to have) a house, duplex or triplex; no new units in the Poudre River 100-year floodplain [1] |
|---|---|
| How many | One ADU on most properties; some zones may allow a second detached house on the lot [1] |
| Detached ADU max size | 750 sq ft if the main home is under 1,667 sq ft; otherwise 1,000 sq ft or 45% of the home, whichever is less; converted accessory buildings up to 800 sq ft [1] |
| Attached ADU max size | Above grade: 750 sq ft or 45% of the main home; basement: 750 sq ft or 100% of that floor [1] |
| Height | Detached ADU no taller than the main building or the zone maximum [1] |
| Location | Detached ADUs behind the front wall of the home, at least 5 ft from other buildings, within zone setbacks [1] |
| Parking | No extra parking beyond what the main home needs [1] |
| Review | Basic Development Review decided by staff; no neighborhood meeting, but notice is posted or mailed [1] |
| Fees | $6,925 Basic Development Review fee; city estimates $20,000-$25,000 total [1] |
| Electric meter | Each ADU needs its own [1] |
| Short-term rental | Not allowed in ADUs that applied for a building permit on or after Jan. 1, 2024 [2] |
| State ADU law | A HB24-1152 subject jurisdiction and a certified ADU Supportive Jurisdiction (as of Oct. 9, 2026) [6][8] |
On this page
What you can build here
Fort Collins says that starting in February 2025, Colorado's ADU law, HB24-1152, allows ADUs in all Fort Collins zone districts, as long as your property meets city requirements. See our Colorado ADU law page.
An ADU is a small home on the same property as a larger house, duplex or triplex. It must have a kitchen, bathroom and living area, and it can be attached (such as a basement unit or an addition) or detached (such as a cottage or a garage apartment).
- Most properties can add one ADU.
- In some zones (RUL, RF, CC, CCN, CCR, CG, CS, CL, LMN, MMN, HMN, NC, D, HC, E, I and RC) you may be able to build a second detached house on the lot, if you meet the usual development standards.
- No new units are allowed in the Poudre River 100-year floodplain. State law also exempts floodway and 100-year floodplain lots from its ADU requirements.
The ADU must be subordinate to the main home, and the land can't be split into separate lots. The Land Use Code says this doesn't rule out a condominium plat. [1][2][3]
Size, height and location
Detached ADUs:
- Up to 750 square feet if your main home is smaller than 1,667 square feet.
- Up to 1,000 square feet or 45% of the main home, whichever is less, if the home is larger.
- An existing accessory building can be converted to an ADU of up to 800 square feet.
Attached ADUs: above grade, up to 750 square feet or 45% of the main home; in a basement, up to 750 square feet or 100% of that floor. The city's page doesn't say whether the lesser or the greater of those two limits applies to above-grade units. HB24-1152 treats as "restrictive" a local standard that "does not allow for accessory dwelling unit sizes between five hundred and seven hundred fifty square feet," though a city may cap an ADU at the size of the main home. If 45% of your home would be under 500 square feet, confirm with Development Review at 970-221-6689 what size it will approve.
Height. A detached ADU can't be taller than the main building or the zone's maximum.
Location. A detached ADU must sit behind the front wall of the house and at least 5 feet from other buildings (more if fire-safety building requirements can't otherwise be met). It must meet the zone's setbacks. A walkway must connect the ADU's main door to the street, and the address must be visible from the street. [1][3]
Parking
No extra parking is required for an ADU beyond what the main home already needs. For reference, a house needs one off-street space if the lot is wider than 40 feet, or two if it is narrower. A duplex needs one space per unit with one or two bedrooms, and two for units with three or more. HB24-1152 bars covered cities from requiring a new off-street space for an ADU, except in narrow cases. [1][3]
Utilities, stormwater and building code
Each ADU needs its own electric meter. In some cases you may need to upgrade nearby transformers or pay for trenching. Utility lines, trees and landscaping have spacing rules: 10 feet between water and sewer lines, 10 feet between storm drains and other utilities, 6 feet between trees and water or sewer lines, and 4 feet between shrubs and those lines. A project that adds more than 1,000 square feet of impervious surface needs stormwater quality treatment, such as rain gardens or permeable pavers.
The Building Code requires fire-rated separation and separate heating for attached ADUs, minimum kitchen and bathroom standards, and separate exit doors. [1]
Fees and timeline
Fort Collins lists these ADU fees:
- Basic Development Review: a flat $6,925, required for every ADU.
- Utility fees: water, sewer and electric capacity charges.
- Transportation fees: Larimer County road impact fees and city capital expansion fees.
- Building permit fees: based on project value and other details.
The city says total fees for an ADU "may be in the range of $20,000-$25,000." HB24-1152 lets cities keep charging generally applicable impact fees. DOLA's ADU Grant Program page lists a $157,000 award to the City of Fort Collins in May 2026 for a "Pre-approved ADU Program and Fee Waiver Support." The grant goes to the city, not to homeowners, and the city's ADU page doesn't yet describe a fee waiver or pre-approved plans, so ask Development Review whether either is available. See our ADU cost guide.
The city doesn't publish a review time for ADUs. Development Review comes first, then the building permit. See our ADU permit process guide. [1][3][4]
Garage conversions
You can convert an existing accessory building, such as a detached garage, into an ADU of up to 800 square feet. It still goes through Basic Development Review and a building permit, and it must meet the building code and utility rules above. The city says no extra parking is required beyond what your main home already needs (one or two spaces, depending on lot width). If your garage holds that parking, confirm with Development Review how the conversion affects it; state law bars covered cities from requiring a new off-street space for an ADU except in narrow cases. See our garage conversion guide. [1][3]
Renting it out
Fort Collins' Land Use Code says ADUs that apply for a building permit on or after January 1, 2024 "shall not be used for a short term rental." Short-term rental licenses issued before that date may be renewed, or a new license may be issued under Section 15-646 of the City Code. HB24-1152 lets cities regulate short-term rental of ADUs.
For long-term rentals (30 days or more), most rental properties must register with the city every year and self-certify that they meet minimum housing standards. The base fee is $37 a year per property, plus $10 for each additional unit on the same property. Contact the Rental Housing program at 970-416-2305.
The city's ADU page doesn't mention an owner-occupancy rule. Under HB24-1152, a covered city can't require you to live on the property, though it may ask you to show you live there when you apply. [1][2][3][5]
Financing and state programs
Fort Collins is on DOLA's list of certified ADU Supportive Jurisdictions as of October 9, 2026. Homeowners there may qualify for the Colorado Housing and Finance Authority's ADU interest rate buydown or credit enhancement programs through a lender of their choice. CHFA describes the programs as supporting ADUs for low- and moderate-income borrowers and/or tenants. See CHFA's ADU finance programs and our ADU financing guide. To compare, see our Denver and Boulder pages. [6][7]
Permit steps in Fort Collins
Check eligibility, zoning and floodplain
Check your zone and whether you're in the Poudre River 100-year floodplain on the city's FCMaps. You need, or must be allowed to build, a house, duplex or triplex on the lot. [1]
Design to the ADU rules
Check size, height, location and setbacks. The ADU's main door needs a walkway to the street, and its address must be visible from the street. [1]
Plan utilities, trees and stormwater
Each ADU needs its own electric meter, and you may need a transformer upgrade or trenching. Keep water and sewer lines 10 feet apart, and trees 6 feet from them. Adding more than 1,000 square feet of roof or paving requires stormwater quality treatment. [1]
Optional: free Conceptual Design Review
Meet city staff through a free Conceptual Design Review to learn about costs, utility connections and site issues before you apply. [1]
Apply for Basic Development Review
Every ADU goes through a Basic Development Review ($6,925 flat fee). Planning, Utilities, Fire, Stormwater and other departments review it, and the Planning Manager or Community Development Director decides. Notice is posted or mailed; no neighborhood meeting is required. [1]
Apply for a building permit
After approval, apply for a building permit by emailing your documents to buildingservices@fortcollins.gov. [1][9]
Build and pass inspections
Build to the approved plans and pass city inspections throughout construction. [1]
Who to call
-
Development Review, Planning and Zoning
ADU eligibility, rules and Development Review; or use the city's online inquiry form
-
Building permit applications: buildingservices@fortcollins.gov
-
Annual rental registration: rentalhousing@fortcollins.gov
281 N College Ave., Fort Collins, CO
Questions people ask
How big can an ADU be in Fort Collins?
A detached ADU can be 750 square feet if your home is under 1,667 square feet, or up to 1,000 square feet or 45% of the home, whichever is less, if it's larger. A converted accessory building can be up to 800 square feet. [1]
How much does it cost to permit an ADU in Fort Collins?
The Basic Development Review alone is a flat $6,925. With utility capacity charges, transportation fees and building permit fees, the city says total fees may be $20,000 to $25,000. [1]
Do I need extra parking for an ADU in Fort Collins?
No. You only need the parking your main home already requires. [1]
Can I Airbnb my ADU in Fort Collins?
Not if the ADU applied for its building permit on or after January 1, 2024. Short-term rental licenses issued before that date may be renewed, or a new license may be issued under Section 15-646 of the City Code. [2]
Is there a public hearing for an ADU in Fort Collins?
No neighborhood meeting is required. City staff (the Planning Manager or Community Development Director) decide the Basic Development Review, and notice is posted or mailed. [1]
Sources (9)
- Accessory Dwelling Units (ADUs), City of Fort Collins Development Review. Accessed October 9, 2026.
- Land Use Code, Article 4: Use Standards, City of Fort Collins. Accessed October 9, 2026.
- House Bill 24-1152, Concerning Increasing the Number of Accessory Dwelling Units (Signed Act), Colorado General Assembly. Accessed October 9, 2026.
- Accessory Dwelling Unit (ADU) Grant Program, Colorado Department of Local Affairs, Division of Local Government. Accessed October 9, 2026.
- Rental Housing, City of Fort Collins. Accessed October 9, 2026.
- ADU Supportive Jurisdictions, Colorado Department of Local Affairs, Division of Local Government. Accessed October 9, 2026.
- Accessory Dwelling Unit (ADU) Finance Programs, Colorado Housing and Finance Authority. Accessed October 9, 2026.
- Accessory Dwelling Units, Colorado Department of Local Affairs, Division of Local Government. Accessed October 9, 2026.
- Building Permits, City of Fort Collins Building Services. Accessed October 9, 2026.