Accessory Dwelling Units

The legislative declaration (C.R.S. 29-35-401) in HB24-1152 highlights that Accessory Dwelling Units (ADUs) provide more housing options for smaller and lower-income households, and elderly individuals who wish to age in their neighborhoods. By allowing the construction of these smaller, more affordable units in areas where utilities and infrastructure are already in place, ADUs present a viable alternative to low-density, dispersed development.

This can help reduce water usage, greenhouse gas emissions, infrastructure costs, and household transportation and energy expenses. Because single-family detached home neighborhoods often occupy a large percentage of land in Colorado communities, allowing ADUs in those areas can serve as an important way to increase housing supply with minimal impacts on their neighborhoods, and can increase attainable and affordable housing options in high opportunity neighborhoods. After requiring that local governments reduce barriers to ADUs, California estimates that ADUs now make up to 20 percent of new housing constructed in that state (Accessory Dwelling Units (ADUs) in California | Bipartisan Policy Center). 

Better aligning ADU regulations across many Colorado communities can help achieve economies of scale by reducing the variability of regulations between jurisdictions, thereby enabling more standardized and modular ADU designs, a more robust market of ADU developers, and associated cost reductions.

Summarized from C.R.S. 29-35-402(21)

The law applies to Subject Jurisdictions, which include:

• Colorado Home Rule or statutory cities and towns, Territorial Charter cities and towns, and consolidated cities and counties, that are within a Metropolitan Planning Organization and have a population of 1,000 or more as reported by the State Demography Office; and
• Those portions of Colorado counties, including Home Rule counties, that are within a Metropolitan Planning Organization and within a Census Designated Place with a population of 40,000 or more as reported in the most recent federal decennial Census.
• However, any jurisdiction may voluntarily comply with HB24-1152 to become eligible for the  ADU Fee Reduction and Encouragement grant program. Additional information is within the Certification Process section below.

The following is a list of Subject Jurisdictions:

• Arvada
• Aurora
• Bennett
• Berthoud
• Boulder
• Brighton
• Broomfield
• Castle Pines
• Castle Rock
• Centennial
• Cherry Hills Village
• Colorado Springs
• Columbine Valley
• Commerce City
• Dacono
• Denver
• Eaton
• Edgewater
• Englewood
• Erie
• Evans
• Federal Heights
• Firestone
• Fort Collins
• Fort Lupton
• Fountain
• Frederick
• Fruita
• Glendale
• Golden
• Grand Junction
• Greeley
• Greenwood Village
• Hudson
• Johnstown
• Kersey
• Lafayette
• Lakewood
• La Salle
• Littleton
• Lochbuie
• Lone Tree
• Longmont
• Louisville
• Loveland
• Lyons
• Manitou Springs
• Mead
• Milliken
• Monument
• Nederland
• Northglenn
• Palisade
• Palmer Lake
• Parker
• Platteville
• Pueblo
• Severance
• Sheridan
• Superior
• Thornton
• Timnath
• Westminster
• Wheat Ridge
• Windsor
• Woodland Park
• Highlands Ranch (Unincorporated Douglas County)

Summarized from C.R.S. 29-35-403(1)

By June 30, 2025, a Subject Jurisdiction must allow one ADU as an Accessory Use to a Single-unit Detached Dwelling in any area, lot, or parcel where the jurisdiction allows Single-unit Detached Dwellings. The ADU must be allowed to be either internal to, attached to, or detached from the Single-unit Detached Dwelling.

Applications for ADUs must be reviewed through an Administrative Approval Process that does not include a public hearing. Approval or denial must be based on compliance with Objective Standards included in the land use code or other ADU regulations. The land use code and/or architectural design standards may not include Restrictive Design or Dimension Standards. These requirements apply to all lots that allow the construction of Single-Unit Detached Dwellings regardless of whether the lot or parcel is located in a standard zone district, overlay zone district, or a Planned Unit Development, and regardless of whether restrictive declarations, bylaws, or rules of an HOA prevent ADUs. 

Summarized from C.R.S. 29-35-403(2), 29-35-403(3), 29-35-402(18)

Subject Jurisdictions may not restrict ADUs in some ways, but are still allowed to regulate ADUs in a number of other ways, as summarized in the table below. More detail is available in the text of the law and in the guidance section.
 

*These requirements do not apply to Exempt Parcels as defined in the law. A Subject Jurisdiction may opt to formalize the allowances for Exempt Parcels in its code.

Subject Jurisdictions who are reviewing current zoning and land development regulations for alignment with the requirements of HB 24-1152 should focus on the following. Example code amendments may be found in the Tools & Resources section below.

The definition of an Accessory Dwelling Unit (ADU)

Summarized from C.R.S. 29-35-402(2)

While the law includes a definition of Accessory Dwelling Unit, it does not require that Subject Jurisdictions adopt that definition. It gives Subject Jurisdictions the right to exclude motor homes, recreational vehicles, and other specific types of housing from the definition, or to include them. However, the Subject Jurisdiction’s definition of ADU may not result in restricting or prohibiting ADUs that would be permitted under the law’s definition such as an attached or internal ADU, or an ADU that is a detached structure.

The list(s) or table(s) of allowed uses in each zone district

Summarized from C.R.S. 29-35-403(1)

In general, ADUs should be listed (or included in a table) as an allowed or accessory use in every zone district where Single-Unit Detached Dwellings are an allowed use (including PUDs). In zone districts where Single-Unit Detached Dwellings are a conditional or special use, ADUs must be allowed as an accessory use to an existing Single-Unit Detached Dwelling. Instead of including this information in a table, Subject Jurisdictions may include language in their development codes clearly indicating that ADUs are allowed in conjunction with all Single-Unit Detached Dwellings in their jurisdiction. This applies regardless of whether Local Law uses a different zoning or regulatory term for a freestanding house on a single lot designed for occupancy by a single household. 

NOTE: This guidance generally uses the term 'allowed' in conformance with the law, but Subject Jurisdictions may use 'permitted' or any other similar terms that clearly indicate an ADU may be constructed.

The procedures for approval of an ADU

Summarized from C.R.S. 29-35-402(5a), 29-35-402(17), and 103(1)

Zoning and land development regulations should be reviewed to ensure that applications for ADUs are subject only to an Administrative Approval Process using Objective Standards, and to remove any requirements for a public hearing before approving an ADU. If the Local Laws allow an administrative decision to be "elevated," "sent up," "referred," or "called up" to an appointed or elected body for review and decision, those provisions should be modified to exclude ADUs from potential public hearing requirements. 

There is one exception: If the ADU is located in a locally designated historic district, and the Subject Jurisdiction has been designated by History Colorado as a Certified Local Government, the application can be subject to the public hearing requirements applicable to other historic district properties. The standards applied in this process must be locally adopted historic regulations or the Secretary of State’s historic preservation standards.

An appeal of an administrative decision to a Board of Adjustment or Planning Commission, for example, is allowable under the law's definition of Administrative Approval Process. The appeal should be limited to a review of the project in relation to the Objective Standards that governed the administrative decision, rather than any subjective determination outside of those Objective Standards.

The standards, conditions, and criteria for approval of ADUs

Summarized from C.R.S. 29-35-402(17)

Standards and conditions applicable to ADUs will require careful review to meet the requirement of HB24-1152. They must be "Objective", which means standards using a defined benchmark or criterion that allows for decisions to be made consistently regardless of who makes the decision. These standards cannot require subjective determinations of whether the application is consistent with adopted plans (including comprehensive or development plans); compatible with the land use or development of the surrounding area; or consistent with public welfare, community character, or neighborhood character.  Although not listed in HB24-1152, decision criteria such as "compatible", "harmonious", "attractive", "similar", and "contributing" are generally considered subjective standards. 

The requirement for Objective Standards applies regardless of whether they appear as "use-specific standards" or "performance standards" applicable to the ADU use in particular, or as decision criteria that staff must use in determining whether to issue a specific type of permit or decision.

Parking regulations

Summarized from C.R.S. 29-35-403(2a), (3a), and (3b)

The law prohibits Local Laws from requiring that a new parking space be constructed or available for each ADU, but does provide two exceptions: 

1. The Subject Jurisdiction may require the designation of an existing parking space on the lot for the use of the ADU, if such a parking space already exists at the time the ADU is constructed or converted. 
2. The Subject Jurisdiction may require the construction of a new off-street parking space if: 
   1. The ADU is in a zone district that, as of January 1, 2024, required one or more off-street parking spaces for a Single-Unit Detached Dwelling; and 
   2. There is no existing parking space on the lot (including a driveway, garage, or tandem parking space) that could be used for the ADU; and 
   3. The ADU is located on a block where the Subject Jurisdiction prohibits on-street parking.

ADU sizes and setbacks regulations

Summarized from C.R.S. 29-35-402(18b), 402(18c), 403(d), and 403(3c)

HB24-1152 contains language that establishes a minimum right to ADUs that are between 500 and 750 square feet (sqft) in size. Subject Jurisdictions may also choose to also allow ADUs smaller than 500 feet or larger than 750 feet. Subject Jurisdictions may also require ADUs be no larger than the Single-Unit Detached Dwelling on the lot. 

Example: A jurisdiction adopts a development regulation stating ADUs can be no larger than 50% of the floor area of the primary dwelling unit. Under this regulation, a property with a house that is 800 sqft would be limited to 400 sqft ADU which is below the 750 sqft that jurisdictions are required to allow. In this interpretation, to comply with state law, the local code would also have to say something like, "the square footage of an ADU shall not exceed fifty (50) percent of the square footage of the principal structure. Except where the principal structure is less than one thousand, five hundred (1,500) square feet, the ADU shall not exceed seven hundred and fifty (750) square feet, but in no case shall exceed the square footage of the principal structure."

Additionally, minimum side setbacks may not be larger than those that apply to the Single-Unit Detached Dwelling on the lot. Minimum rear setbacks may not be larger than those that apply to other accessory building types in the same zone, or five feet, whichever is greater.

Owner occupancy on lots with ADUs

Summarized from C.R.S 29-35-403(2b)

The law prohibits Local Laws from requiring that the Single-Unit Detached Dwelling or the ADU be occupied by the owner of the lot. The law provides two exceptions: 

1. Local Law can require evidence that the owner resides on the lot at the time an application for construction or conversion of an ADU is filed (but this exception does not apply if the ADU and new Single-Unit Detached Dwelling are being constructed at the same time). 
2. Local Law may require evidence that the owner resides on the lot at the time an application for a license or permit allowing short-term rental of the ADU is filed.  

Planned Unit Developments (PUDs)

Summarized from C.R.S. 24-67-105(5.3)

Two separate provisions of the law address its impact on Planned Unit Developments: The first applies to approved PUDs and the second to future PUDs.

The law applies to areas of approved Planned Unit Developments that allow the construction of Single-Unit Detached Dwellings to the same extent it applies to other properties in non-PUD developments. Meaning, in areas where Single-Unit Detached Dwellings are allowed, ADUs must be allowed as an accessory use to a Single-Unit Detached Dwelling regardless of whether the PUD is silent on ADUs and/or accessory uses, or prohibits ADUs. The approval, permitting, and construction of an ADU in a PUD development shall also only be subject to an Administrative Approval Process subject to only Objective Standards.

The law also provides that future PUDs may not contain provisions that restrict the construction or conversion of ADUs in ways not permitted by the law.

Subject Jurisdictions should consider incorporating language within the portion of their land use and development codes that grants the authority to create PUD zone districts stating:

• Future PUD zone districts which permit Single-unit Detached Dwellings shall not restrict the allowance of ADUs as an Accessory Use subject to an Administrative Approval Process; and
• Existing PUD zone district regulations pertaining to ADUs and/or Accessory Uses may be superseded by the adoption of local laws pursuant to CRS 29-35-403.

A Subject Jurisdiction should consult with their city attorney to determine the appropriate language. 

No later than June 30, 2025, every Subject Jurisdiction must file a report with DOLA demonstrating that the community has complied with the requirements of the law. The report must be submitted by 11:59 p.m. on June 30, 2025. DOLA may approve an extension of up to six months if the Subject Jurisdiction demonstrates that it has: 

• Initiated the process of compliance, 
• A timeline for completion of that process, and 
• Explained the reason for not meeting the initial compliance deadline.

DOLA is in the process of developing a web-based portal for submissions. If jurisdictions would like to prepare their submission materials before the portal is available, please refer to the Form & Manner document in the Tools & Resources section below. While there may be some minor updates in the web portal, we expect the required information to stay consistent.

Summarized from C.R.S. 29-35-404(1a), (2), and (3)

HB24-1152 contains provisions allowing Colorado communities to seek designation as an ADU Supportive Jurisdiction, whether or not they are a Subject Jurisdiction required to comply with the law.

In order to achieve this designation, Colorado communities must comply with the requirements of the law, and also implement at least one of 10 supportive strategies to promote the construction, conversion, or use of ADUs. While nine of those strategies are defined in the law, the tenth is an option allowing for any additional strategy suggested by the community and approved by DOLA to achieve those goals. These strategies are listed and described in a document within the Tools & Resources section below. This document also contains examples in and outside of Colorado, and discussion on the pros and potential cons with each strategy. Implementation of at least one of those 10 strategies must also be documented in the report due by June 30, 2025.

Designation as an ADU Supportive Jurisdiction is documented by a certificate issued by DOLA, which makes the Subject Jurisdiction, or voluntary community, eligible to apply for grants under a new Accessory Dwelling Unit Fee Reduction and Encouragement Grant Program. Subject Jurisdictions are encouraged to take the additional step necessary to achieve this designation, as the state may in the future make additional resources and assistance available to ADU Supportive Jurisdictions.

Summarized from C.R.S. 38-33.3-106.5(4)

Three provisions of the law address restrictive covenants that may apply to neighborhoods with Single-Unit Detached Dwellings.

In Subject Jurisdictions, HOA covenants adopted on or before June 30, 2025 may not be applied to restrict the creation of an ADU in any way that is prohibited by the law. Similarly, restrictive covenants created after June 30, 2025, may not contain provisions that restrict the creation of an ADU in ways that are prohibited by the law. As a practical matter, these provisions mean that the courts of Colorado will not be available to enforce restrictive covenants that violate these requirements.

A third provision allows HOAs to continue to apply "Reasonable Restrictions" on ADUs. A Reasonable Restriction is defined as "a substantive condition or requirement that does not unreasonably increase the cost to construct, effectively prohibit the construction, or extinguish the ability to otherwise construct an ADU" pursuant to the law. Among other things, an HOA may apply standards and conditions to ADUs if those standards are also applied to the construction of other types of accessory buildings.  They may apply standards and conditions to the creation of an ADU within an existing Single-Unit Detached Dwelling if they would apply the same standards and conditions to other internal modifications of the house.

NOTE: SB24-174, also passed by the General Assembly during its 2024 session, includes a similar provision for Common Interest Ownership Associations (i.e. condominium associations). After June 30, 2024, it prohibits them from adopting new regulations that prohibit or restrict the construction of ADUs if the zoning laws of the local jurisdiction would otherwise allow ADUs.

Summarized from C.R.S. 29-35-402

This section lists several key terms defined in the law. Please note that the law contains numerous additional definitions that may be important in specific contexts.

"Accessory Dwelling Unit" means an internal, attached, or detached dwelling unit that: (a) provides complete independent living facilities for one or more individuals; (b) is located on the same lot as a proposed or existing primary residence; and (c) includes facilities for living, sleeping, eating, cooking, and sanitation.
NOTE: Subject jurisdictions are not required to adopt this definition of an ADU, but the use of a different definition cannot result in more restrictions on ADUs than are permitted by the law. For example, subject jurisdictions’ definitions must include internal, attached, and detached ADUs.

"Administrative Approval Process" means a process in which: (i) a development proposal for a specified project is approved, approved with conditions, or denied by local government administrative staff based solely on its compliance with Objective Standards set forth in local laws; and (ii) does not require, and cannot be elevated to require, a public hearing, a recommendation, or a decision by an elected or appointed public body or a hearing officer.

"Exempt Parcel" means a parcel that is: (a) not served by a domestic water and sewage treatment system, as defined in section 24-65.1-104 (5), or is served by a well with a permit that cannot supply an additional dwelling unit; (b) a historic property that is not within a historic district; or (c) in a floodway or in a one hundred year floodplain, as identified by the federal emergency management agency.

"Local Law" means any code, law, ordinance, policy, regulation, or rule enacted by a local government that governs the development and use of land, including land use codes, zoning codes, and subdivision codes.

"Objective Standard" means a standard that: 

1. Is a defined benchmark or criterion that allows for determinations of compliance to be consistently decided regardless of the decision maker; and 
2. Does not require a subjective determination concerning a development proposal, including but not limited to whether the application for the development proposal is: 
   1. Consistent with master plans, or other development plans; 
   2. Compatible with the land use or development of the area surrounding the area described in the application; or 
   3. Consistent with public welfare, community character, or neighborhood character.

"Restrictive Design or Dimension Standard" means a standard in a Local Law that: 

1. Requires an architectural style, building material, or landscaping that is more restrictive for an Accessory Dwelling Unit than for a Single-Unit Detached Dwelling in the same zoning district; 
2. Does not allow for Accessory Dwelling Unit sizes between five hundred and seven hundred fifty square feet; 
3. Requires side setbacks for an Accessory Dwelling Unit that are larger than the side setbacks required for a primary dwelling unit in the same zoning district; 
4. Requires a rear setback for an Accessory Dwelling Unit that is larger than the greater of: 
   1. The rear setback required for other accessory building types in the same zoning district; or 
   2. Five feet; 
5. Is a more restrictive minimum lot size standard for an Accessory Dwelling Unit than for a Single-Unit Detached Dwelling in the same zoning district; or 
6. Applies more restrictive aesthetic design or dimensional standards to Accessory Dwelling Units that are factory-built residential structures, as defined in section 24-32-3302 (10), than other Accessory Dwelling Units.

"Single-Unit Detached Dwelling" means a detached building with a single dwelling unit on a single lot.