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Building an Accessory Dwelling Unit - Type 1 Review#

A geographic map showing an outline of the City of Fort Collins with the Old Town residential zone districts shaded black.

Old Town residential districts, OT-A, OT-B or OT-C

An Accessory Dwelling Unit (ADU) is a small house or unit that is on the same property as a larger building. 

An ADU: 

  • Contains everything someone needs to live in a home: a kitchen, bathroom and living area.
  • Is on the same property or lot as another primary dwelling unit.
  • Is smaller than the primary dwelling unit and is located to the rear of the primary unit.
  • Can be attached to a house or detached.

If you are looking to build a detached ADU, your project will need to go through a certain level of review through our development review process. This is dependent on the zone district your property is located in. 

What is a Type 1 Review? A Type 1 Review will require your project to be reviewed and approved by an Administrative Hearing Officer at a public hearing.

How do I find out if I need one? In order to determine if your ADU project is subject to a Type 1 level review, check out your zoning. Search for your address or check our zoning map

If your property is located in an Old Town residential zoning, OT-A, OT-B, or OT-C, your project will need to go through a Type 1 Review.

Not able to build an ADU in your zone district? Learn more about other options for adding dwelling units on your property.

Top Considerations For an ADU#

Below, we have listed some of the major items to consider when it comes to thinking about building an ADU on your property.

  • Going through the Development Review Process: Staff time spent reviewing development project proposals is split between taxpayers and applicants. https://www.fcgov.com/developmentreview/fees 

  • Fees for electric service: These could include electric capacity fees, building site charges and any system modification charges necessary to serve the ADU project.  https://www.fcgov.com/utilities/business/builders-and-developers 

  • Transportation infrastructure improvements: If building an ADU will trigger the need for any road or sidewalk improvements in your area, you may be asked to help pay for those. 

  • Larimer County Road Impact Fees and Transportation Capital Expansion Fees: These will need to be paid before you can get a building permit. https://www.fcgov.com/engineering/tcef  

  • Development and water supply fees (WSR): These will be due at the time the building permit is issued. Please contact our Utility Fee and Rate Specialists at (970) 416-4252 or UtilityFees@fcgov.com for more information or questions. Information on fees can also be found at: www.fcgov.com/development-fees

  • Building fees: A plan review fee will be collected at the time of plans submittal on all work valued over $3,000. The building permit and any other applicable fees will be paid at the time the permit is issued. See Building Permit Fee Schedule

Is my property in a floodplain? If your property is in the Poudre River 100-year floodplain, you may not add any dwelling units. 
Is my property in this floodplain? Check our floodplain map.

Zone District Lot Area
OT-A 12,000 square feet min.
OT-B 10,000 square feet min.
OT-C No lot size requirement

Separation Requirements#

  • On smaller sites, it can be difficult to find space to meet rules about how far varying utilities need to be located from other things.  

  • For your reference, minimum water and sewer service separations are:

    • More than 10 feet between water and sewer services

    • More than 6 feet between trees and water or sewer services

    • More than 4 feet between shrubs and water or sewer services

    • More than 10 feet between storm drain pipes and other utilities 

    • Service lines of the same type may be placed together in the same trench but they will need to be separated by at least 3 feet. 

  • Other utilities, such as gas, electric and communications will also have spacing requirements and will need space on the site.
  • Please remember that there may be service lines on neighboring properties and you will need to keep your utilities separated from those as well.  
  • If you plan to plant more trees as part of this project, please keep them away from utility lines. We recommend:

    • Six feet between trees and water or sewer lines 

    • Four feet between trees and gas lines 

    • Ten feet between trees and electrical vaults.  

Walkway Connections#

You will be required to provide a walkway from the main door of the ADU to the approved Emergency Access road. This walkway is required to provide access for emergency personnel and equipment. 

Sprinkler Requirements#

Poudre Fire Authority will need to make sure they have access to all exterior portions of any building.  Access is required within 150 feet of any exterior portion of a building and can be considered from any public street or private street meeting fire lane requirements.  If access within 150 feet cannot be achieved, the installation of an approved NFPA 13D fire sprinkler system can extend the access distance to 300 feet. 

Stormwater Quality Treatment#

If the improvements create more than 1,000 square feet of new impervious area, stormwater quality treatment will be required for those new areas. Options could include directing downspouts into landscaped areas, disconnecting impervious areas, installing rain gardens, and using permeable pavers. 

Considerations For ADUs From All Departments#

An image showing multiple primary single unit homes with accessory dwelling unit structures behind them.

Below, you can find each departments' primary considerations for ADUs that require a Type 1 Review. Each property is unique, so the exact details of what reviewers are seeing when they review your project may differ from what is below. 

  • For an Accessory Dwelling Unit (ADU) to be approved in your zone district, it will need to be reviewed and approved by an Administrative Hearing Officer at a public hearing. After your application has been submitted, it will undergo a few rounds of edits between you and City staff, which could take several months. When the application is ready to be presented at a hearing, please allow 4-6 weeks to schedule a hearing to accommodate scheduling requirements, including posting and mailed public notices. 

  • For the hearing, nearby property owners within 800 feet will be formally notified by letter. We will send out these letters and work with you to set the hearing date. 

  • You won’t be required to hold a neighborhood meeting to build an ADU. We can help you organize one if you’d like to inform your neighbors beforehand. A neighborhood meeting is a good opportunity to receive early feedback from your neighbors. Hearing this feedback can help you to address any concerns they may have prior to the public hearing. 

  • Your first step is to have a free Conceptual Design Review meeting with City Staff. The application for this meeting is on our website: https://www.fcgov.com/developmentreview/applications  

  • During this meeting we will explain more about the Development Review Process. You can find additional information on our website: https://www.fcgov.com/developmentreview/why-development-review  

  • There are planning fees associated with this development project and you will receive a formal estimate of your fees when you submit your application.  https://www.fcgov.com/developmentreview/fees

  • There may be additional fees from other departments during the development review process and the building permit process. Fee schedules are subject to change. 

  • When you submit your Development Review Application, a yellow Development Review sign will be placed on your property. The sign will remain until a final decision is made at the hearing and any appeals have been processed.  

  • This property is located in an Old Town Zone District (OT-A, OT-B or OT-C). These zone districts have rules which you can find in Article 2, Section 1.6 of the Land Use Code. https://www.fcgov.com/planning-development-services/luc

  • In these zone districts, an Accessory Dwelling Unit (ADU) is subject to review by an administrative hearing officer.

  • If this property isn’t platted (in other words, isn’t shown on a previous subdivision plat map), then you will need to get a legal plat created by a licensed professional surveyor.

  • For your lot to have an ADU, it must:

    • Be at least 40 feet wide (along the street frontage).

    • Have a minimum area of: 

Zone District Lot size required by ADU (min)
OT-A 12,000 square feet
OT-B 10,000 square feet
OT-C No lot size requirement
  • A “setback” is the minimum distance a building can be from a property line. In the Old Town Zone Districts, your setbacks are:
    • Front: 15 feet
    • Side (interior a block): 5 feet
    • Side (next to a street on a corner lot): 9 feet
    • Rear (if there is no alley): 15 feet
    • Rear (if there is an alley): 5 feet 
  • Additional setbacks for garages in these zone districts are: 
    • Setback from a public sidewalk: at least 20 feet 
    • Setback of a garage door from a side or rear alley: 8 feet 
  • No permanent building may be built in an easement. Easements are areas set aside for things like utilities, emergency access or drainage. They are part of your property but have additional restrictions on them. When you submit your application, please show any known easements with their dimensions and purpose on your site plan.  
  • You may only have one ADU on your property.
  • ADUs may not be used for Short-Term Rentals (Airbnb, VRBO, etc.)
  • A detached ADU in the Old Town Zone Districts can be built behind any detached house, duplex or triplex. It must be built at least 10 feet behind the front wall of that primary building. 
  • Accessory Dwelling Units that are attached to the main house are not permitted in the Old Town Zone Districts. 
  • An ADU must be at least 5 feet from all other buildings. If it is between 5 and 10 feet of another building, you will need to build it out of special materials to meet fire safety rules. You will also have limitations on the openings (windows, doors, etc.) that you can build in those walls. 
  • The OT Zone Districts have protections on backyards, or limits on the mass of construction in the rear yard. Only a certain amount of floor area can be built on the rear half of a lot:  
Zone District Floor area allowed on the rear half of the lot
OT-A 25% of the rear; 50% of the lot area
OT-B 33% of the rear; 50% of the lot area
OT-C 33% of the rear; 50 % of the lot area

Floor area is the footprint of the building plus any second-floor area that has a ceiling height of 7 feet 6 inches or greater. All floors above a basement are counted. All buildings, including portions of the primary structure (e.g., house) are counted. This could include a detached garage, an ADU, and any shed over 120 square feet, etc.  

For example:  

A 10,000 square foot lot would have 5,000 square feet in the rear half of the lot. 33% of 5,000 square feet is 1,667 square feet. So, all the area of all the floors of all the buildings (or portions of buildings) in the rear half of the lot may add up to a maximum of 1,667 square feet. Basements generally do not count (unless their ceiling is more than 3 feet above grade/ in a “garden level” situation).  

  • The allowed floor area of the ADU will depend on several factors:
    • The size of the primary structure (the house, duplex or triplex)
    • Will the ADU be new construction or a conversion of an existing structure?
  • The floor area will include all habitable and non-habitable spaces (e.g., garage floor area + ADU floor area both count toward the square footage totals).  
New or existing? Size of primary building (e.g., primary house) Largest allowable floor area of ADU
New construction < 1,335 square feet  600 square feet
New construction > 1,335 square feet 1,000 square feet or 45% of the primary building, whichever is less
Existing accessory structure N/A 800 square feet
  • The ADU can be up to 1.5 stories. In other words, a full first story with a second story no more than 40% of the area of the first floor.

  • The ADU can’t be taller than the primary structure. The maximum allowable height is 24 feet. Any walls of the ADU facing the side yard (interior to a block; corner side yards) may not exceed 13 feet.  

  • There are a variety of architectural design requirements in the Land Use Code. These address things like orientation of entry doors and windows, size of dormers, exterior design features and solar access. Please see the Land Use Code Section 2.1.6 for more information.  

  • You will need to provide one on-site (off-street) parking space for the ADU, in addition to the parking already required for the primary building. Please show the parking spaces on your plans. 

  • The ADU must have a full bathroom and kitchen.  

  • There needs to be a walkway from the ADU to the street. The ADU’s address needs to be visible from where the walkway meets the public sidewalk (i.e., near the front of the primary building). This is so that any friends, emergency services and pizza deliveries can access the unit quickly and easily.  

  • Buildings, structures and open spaces must be located on the property to trees and shrubs, to the extent reasonably feasible.  

  • If your proposal is unable to meet all the rules, you may be able to ask for a Modification of Standard. The criteria for being granted a Modification of Standard are in Section 6.8 of the Land Use Code.  

Following the Development Review Process, you will need to get a building permit. Find our current adopted building codes here: https://www.fcgov.com/building/codes 

  • You may need to upgrade the public electrical system to support the new dwelling unit. If modifications or relocations are necessary, you will need to cover the costs. Light & Power will determine the location of the nearest transformer and any needed upgrades after you submit your project application.  

  • The Accessory Dwelling Unit will need its own electric meter and service lines. You will need to work with Light & Power to determine where the electric service and meter should go. You can find out more information about our metering requirements in our Electric Service Standards, Section 8, on our website: https://www.fcgov.com/utilities/what-we-do/light-power 

  • In most cases, Light & Power will own, maintain and install the service for the ADU at your expense. In some cases, Light & Power will require the owner to provide the trench. If the service is more than 200 amps, the service will need to be owned, maintained and installed by the property owner.  

  • If you build an ADU, you might need to provide a utility easement on the property so that a new transformer that can handle the additional load can be installed and accessed.  

  • The City of Fort Collins now provides high-speed fiber internet, video, and phone services. You can learn more about these residential services on our website. https://fcconnexion.com/residential/ 

  • We also offer significant rebates to Fort Collins Utility customers for installing solar PV units through our Solar Rebate Program. Visit our website to learn more. www.fcgov.com/solar 

  • Easements are areas on your property that are set aside for things like utilities, emergency access or drainage. These areas are part of your property but have additional restrictions on them. Our Engineering team will require you to provide any easements that may become necessary as a part of this project. 

  • If there are already easements on your property, please show them on your site plan when you apply for the ADU project.  

  • We will check your property to see if it has enough right-of-way along the street frontage. Please show this on your site plan when you apply too.  

  • We will check to see if any road or sidewalk improvements will be needed in your area due to this project. If there are, you might need to help pay for these improvements.  

  • We will also check that there are safe access points for vehicles, pedestrians, and cyclists to reach the ADU. If you have an alley behind your property cars might need to use the alley to reach the ADU. You may also be required to pave part of the alley.  

  • If any sidewalks, driveways or ramps on or near your property don’t meet ADA standards, they will need to be fixed as part of your project.  

  • You will need to pay Larimer County Road Impact Fees and Transportation Capital Expansion Fees before getting a building permit. You can find more information at: https://www.fcgov.com/engineering/tcef  

  • Other important details that we provide for every development project:

    • Any curbs, gutters or sidewalks that are damaged must be fixed before your project is completed. 

    • Public improvements must follow Larimer County Urban Area Street Standards, which can be found online. You can contact City staff if you need the link. 

    • Utility plans will be needed, and a Development Agreement will be recorded once the project is finalized. 

    • You will need a Development Construction Permit before starting construction work.

    • The public right-of-way cannot be used for treating stormwater runoff.

    • Any structures you would like to build in the public right-of-way would need to apply for an encroachment permit. Approval may not be granted.

    • The public right-of-way cannot be used for staging materials or parking during construction.  

  • If your project is near one of our protected natural habitats or natural features, you might need to hire a certified ecologist to conduct an Ecological Characterization Study. This helps us understand how your project might affect the environment. You may need to provide an un-developed buffer around those natural habitats or natural features. We can tell you if this Ecological Characterization Study requirement will apply when you submit your project application. You can reach out to our environmental planners at Planning@fcgov.com

  • If you are planning to remove trees, please note that it is prohibited for any person at any time in the city to abuse or injure any wild bird or damage a nest with eggs or to injure the young of any bird. A professional ecologist or wildlife biologist is required to complete a nesting survey 5-7 days before conducting tree removal or trimming. 

  • If any trees will be removed, this text will need to be included on the tree mitigation plan and the landscape plan:  “NO TREES SHALL BE REMOVED DURING THE SONGBIRD NESTING SEASON (FEBRUARY 1 TO JULY 31) WITHOUT FIRST HAVING A PROFESSIONAL ECOLOGIST OR WILDLIFE BIOLOGIST COMPLETE A NESTING SURVEY 5-7 DAYS BEFORE TREE REMOVAL OR TRIMMING TO IDENTIFY ANY ACTIVE NESTS EXISTING ON THE PROJECT SITE. THE SURVEY SHALL BE SENT TO THE CITY ENVIRONMENTAL PLANNER. IF ACTIVE NESTS ARE FOUND, THE CITY WILL COORDINATE WITH RELEVANT STATE AND FEDERAL REPRESENTATIVES TO DETERMINE WHETHER ADDITIONAL RESTRICTIONS ON TREE REMOVAL AND CONSTRUCTION APPLY.”  

  • Poudre Fire Authority will need to make sure they have access to all exterior portions of any building.  Access is required within 150 feet of any exterior portion of a building and can be considered from any public street or private street meeting fire lane requirements.  If access within 150 feet cannot be achieved, the installation of an approved NFPA 13D fire sprinkler system can extend the access distance to 300 feet. 

  • PFA will require a walkway from the main door of the ADU to the approved Emergency Access road.  This walkway is required to provide access for emergency personnel and equipment. 

  • PFA will verify the water supply (Fire Hydrant) to the ADU.  A fire hydrant is required within 400 feet of the proposed ADU and the distance is measured along the approved path of fire apparatus access. 

  • The ADU will need have its address posted in specific places that can help emergency services workers find their way to the building. The address numbers shall be a minimum of 4” in height with a minimum ½” stroke and shall be posted on a contrasting background.  Additional wayfinding signage may be required in order to provide emergency personnel direction to the ADU from the fire apparatus access road.   

  • Any ADU to be located in a City or FEMA regulated floodplain should contact floodplains@fcgov.com to discuss permitting requirements. 

  • If your property is located in the Poudre 100-year floodplain, no new residential units (including ADUs) will be allowed.  

  • If there are trees already on the property, we strongly encourage designing the layout of the ADU to avoid disturbing those trees. This may include not digging or filling the ground within the drip line (under the canopy) of any tree. It may also include putting up berries to protect trees during construction. If you would like more advice on preserving significant trees on your property, please do not hesitate to reach out to us at Forestry@fcgov.com.  

  • If you plan to plant more trees as part of this project, please keep them away from utility lines. We recommend: 

  • Six feet between trees and water or sewer lines 

  • Four feet between trees and gas lines 

  • Ten feet between trees and electrical vaults.

  • In most cases, Historic Review will not be required if you are building an ADU on a residential property with a detached house as the primary dwelling unit.  

  • Historic Review may be required if you are hoping to build an ADU and the primary building is a duplex, triplex, or a detached house that contains a non-residential land use (dentist, insurance agency, architect office, candy shop, etc.). In these cases, Historic Review would be required if the building is at least 50 years old or is designated as a historic resource. You can find out if your property is designated as historic here: https://www.fcgov.com/historicpreservation/fort-collins-landmarks.   

  • Stormwater can check which subdivision or neighborhood your property belongs to. Your project must follow the drainage design approved for that neighborhood. If your property isn’t in a neighborhood that has an approved plan, it must follow the designs in the Master Drainage Plan for your area and the Fort Collins Stormwater Criteria Manual. You can find these criteria here: https://www.fcgov.com/utility-development

  • If your project proposes to change the approved drainage plan, you will need a drainage letter and construction plans to be prepared by a Professional Engineer registered with the State of Colorado. These plans must show existing and proposed drainage patterns, where stormwater runoff will go (stormwater outfall), how to handle extra runoff on neighboring properties, and the areas that don’t absorb water (impervious areas). 

  • You will need to show the existing and proposed impervious areas with a table summarizing the areas with your project application. If the improvements create more than 1,000 square feet of new impervious area, stormwater quality treatment will be required for those new areas. Options could include directing downspouts into landscaped areas, disconnecting impervious areas, installing rain gardens, and using permeable pavers. 

  • You will need to provide a drainage letter and construction plans (site plan, grading & drainage plan, and utility plan) with your application. These will need to be prepared by a Professional Engineer registered in the State of Colorado. These documents will need to: 

  • Show the existing and proposed drainage patterns,  

  • Identify where site runoff is going (stormwater outfall),  

  • Address any need to mitigate additional runoff directed onto neighboring properties (in some cases offsite easements may be required), and  

  • Show the final site impervious areas (buildings, pavement, driveways, etc.).  

  • All plans must be based on the NAVD88 vertical datum. Before starting any surveying or design work, please make sure your consultants are aware of this requirement. Please contact our office for the latest Benchmark Statement format and City Vertical Control Network information.  
  • Technical services has specific naming, surveying and mapping conventions that will need to be followed in order to legally vest a project.  

  • Traffic Operations requires a Traffic Impact Study for some developments. Typically, an ADU would not require a Traffic Impact Study, but in order to waive the study you will need to submit a worksheet with your application. The worksheet is called a Transportation Worksheet (Attachment “C”). Here is a link where you can find the worksheet and learn more about the Traffic Impact Studies we require. https://www.larimer.gov/sites/default/files/uploads/2021/ch04_transportation_impact_studies_0.pdf 

  • When you submit your application, we will review the access points to the property to make sure they meet our standards. The number of access points (e.g. driveways) we allow for one property will vary depending on how your streets are classified (arterial, collector, local, etc.), but in most cases we will want any access to an ADU to be shared with the driveway to the existing building on the site.  

  • If the property currently has more access points than are allowed, one or more may need to be eliminated. Closure of an access point may required you to construct the curb, gutter and sidewalk along the street.  

  • Your property may be within the City of Fort Collins water and sewer service areas, however there are several water and sewer providers within City limits. You can check this map to find out who provides your water service and sewer service and how to contact them.  https://gisweb.fcgov.com/HTML5Viewer/index.html?Viewer=Utility%20Districts The information below is specifically for Fort Collins Utilities customers. If you’re served by a different utility, they might have similar rules for your project, but you’ll need to check with them. 

  • If you are in the Fort Collins water utility district, before you submit your application, please contact us at WaterUtilitiesEng@FCgov.com for information about the existing sewer infrastructure on and near your property. The City can provide you with information about the closest public sewer main (often in a nearby street) and private sewer service (from the water main to the building) to your site. 

  • Fort Collins Utilities water and/or sewer services to an existing residential building can be extended to one additional structure. This requires a covenant agreement for the property that says the lot may not be divided so the extra structure is on a separate lot. If the accessory structure is an ADU, you will need to pay additional water and sewer fees.

  • Development and water supply fees (WSR) will be due at the time the building permit is issued. Please contact our Utility Fee and Rate Specialists at (970) 416-4252 or UtilityFees@fcgov.com for more information or questions. Information on fees can also be found at: www.fcgov.com/development-fees.

  • When you submit your application, you will need to include a utility plan showing how the water and sewer services will be extended to or otherwise provided to the new structure. Generally, this plan is prepared by a Colorado Professional Engineer. 

  • On small sites, it can be difficult to find space to meet rules about how far water utilities need to be located from other things. 

  • For your reference, minimum water and sewer service separations are:

    • More than 10 feet between water and sewer services
    • More than 6 feet between trees and water or sewer services
    • More than 4 feet between shrubs and water or sewer services
    • More than 10 feet between storm drain pipes and other utilities
    • Service lines of the same type may be placed together in the same trench but they will need to be separated by at least 3 feet.
  • Other utilities, such as gas, electric and communications will also have spacing requirements and will need space on the site. Last, please remember that there may be service lines on neighboring properties and you will need to keep your utilities separated from those as well.

What Are My Next Steps?#

This is a rainbow colored image that shows the development phases from pre-application to inspections and compliance.

Ready to Start? Your first step is to have a free Conceptual Design Review meeting with City Staff. The application for this meeting is on our website: https://www.fcgov.com/developmentreview/applications  

You will receive the following with a Conceptual Review: 

  1. Application Checklists specific to your project 
  2. A Letter addressed to your business proposal, documenting requirements for your proposed project 
  3. A detailed outline of what to expect in the Development Review process. 
  4. A 45-minute online meeting with City Staff, including time to answer questions you might have about the development review process. 

More Resources#

Visit our Residents Portal for resources on zoning, land use, and planning & development.

See the full Land Use Code

Visit our Applications Page

Check out other options for adding a second dwelling on your property.

Why Development Review?