Side by side · Colorado
Compare ADU rules across Colorado
Flexible on where you build? The same backyard cottage can be routine in one city and impossible next door. This table puts 23 Colorado cities side by side so you can shortlist the friendly ones before reading a single ordinance, or narrow it to just the cities you are deciding between. Every value is summarized from the city's own code; open a city's page for the full notes, citations, and fine print.
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| City | Detached ADU | Attached / internal | Max size | Owner occupancy | Extra parking | Approval |
|---|---|---|---|---|---|---|
| Arvada | Allowed | Allowed | New construction: the lesser of 40 percent of the main home's living space and a lot-size cap of 600 sq ft (lot 6,000 sq ft or less), 850 sq ft (6,001 to 12,499 sq ft), 1,000 sq ft (12,500 sq ft to 1 acre) or 1,200 sq ft (over 1 acre). An ADU built inside an existing home's footprint is instead capped at 50 percent of the principal dwelling's floor area including the basement. | Required | One on-site parking space for the ADU on top of the parking required for the main house; the space may be in tandem | Permitted use |
| Aurora | Under Aurora's codified Unified Development Ordinance, a detached ADU is a listed use only in the historic Original Aurora area on the city's west side: Table 3.2-1 designates Dwelling Unit, Detached Accessory as a conditional accessory use (CA) in the OA-R1 and OA-R2 subdistricts and a conditional use (C) in OA-RMU, all within the Mixed-Use Original Aurora (MU-OA) district, and leaves it blank (not allowed) in every other district, including all of the R-R, R-1, R-2, R-3, and R-4 single-family districts. Even in MU-OA, the lot must be served by an alley, must exceed 6,000 square feet (single lot or contiguous lots), and must contain exactly one single-family dwelling, with one ADU maximum. Colorado's HB24-1152 (C.R.S. 29-35-403) has required Aurora, a subject jurisdiction, to allow one ADU wherever single-unit detached dwellings are allowed since June 30, 2025, but the City Council voted on June 9, 2025 against the compliance ordinance and the UDO remained unamended as of July 31, 2026, so state law and local code conflict everywhere outside MU-OA. Ordinance read July 2026 | Not allowed | 650 sq ft max; 24 ft height cap | Required | 1 additional off-street space, accessed from the alley | Table 3.2-1 lists detached ADUs as conditional uses in the only districts that allow them (CA in OA-R1 and OA-R2, C in OA-RMU), and conditional uses follow UDO §146-5.4.3.A: the Planning Director reviews the application and forwards a recommendation to the Planning and Zoning Commission, which holds a public hearing and decides against compatibility criteria, with appeal or call-up to City Council. One exception: ADUs in MU-OA that were legally created before the UDO's effective date are deemed permitted uses needing no conditional use approval (§146-3.3.6.G.2.a). HB24-1152 requires subject jurisdictions to approve ADUs through an administrative process with no public hearing; the compliance ordinance that would have made ADUs administratively approved in nine districts (R-R, R-1, R-2, R-3, R-4, OA-R1, OA-R2, MU-A, APZ) was voted down on June 9, 2025, so the hearing-based conditional use process remains the codified procedure. Ordinance read July 2026 |
| Boulder | Allowed | Allowed | Detached: 800 sq ft (1,000 sq ft for an affordable ADU or on a designated historic property). Attached: half the principal structure's floor area or 1,000 sq ft, whichever is less (two-thirds or 1,200 sq ft, whichever is less, for an affordable ADU or designated historic property), with a 750 sq ft floor for small principal homes. | Not required | None. Boulder imposes no minimum off-street motor vehicle parking for any use, ADUs included; Table 9-4 also lists 'no requirement' for ADU bicycle parking. | Permitted use |
| Broomfield | Allowed | Allowed | 500 sq ft allowed on any eligible lot regardless of house size; above 500 sq ft the ADU is capped at the lesser of 50 percent of the principal dwelling's footprint or 800 sq ft (garages and porches excluded from the calculation) | Not required | None in most cases; 1 space only if the lot has no existing off-street parking, adjacent streets do not allow on-street parking, and the lot is outside a Parking Reduction Area | Permitted use |
| Castle Rock | Allowed | Allowed | Interior or addition ADU: greater of 50% of the primary dwelling or 750 sq ft; detached ADU: 800 sq ft building footprint (PD zoning may allow more) | The owner of an existing primary dwelling must demonstrate, as evidenced in Douglas County public records, that the owner resides in the primary dwelling at the time the ADU building permit application is submitted; the town collects a notarized Affidavit of Residency with the application. There is no ongoing owner-occupancy obligation after the permit issues. Ord. 2025-023 (July 1, 2025) repealed the earlier rule, in place under Ord. 2023-007, that required the owner to occupy one of the two units and to record a deed restriction barring renting both units at once. The current at-application check is exactly what C.R.S. 29-35-103(2)(b), enacted by HB24-1152, permits: subject jurisdictions may not require an ADU or any dwelling on the same lot to be owner-occupied, but may require a residency demonstration when the construction application is submitted (an exception that does not apply when the ADU is built simultaneously with a new primary dwelling). Ordinance read July 2026 | None for the ADU: Chapter 17.61 imposes no ADU parking requirement, and state law bars new-space mandates | Permitted use |
| Centennial | Allowed | Allowed | 50% of the principal dwelling's footprint (or the full attic/basement area for an interior conversion); detached ADUs capped at 17 ft tall | Not required | 1 off-street space per ADU, in addition to the 2 required for the house; may sit in an existing driveway | Permitted use |
| Colorado Springs | Allowed | Allowed | 50 percent of the principal structure's floor area or 1,250 sq ft, whichever is less; 750 sq ft allowed if the house is under 1,500 sq ft. Detached ADUs are capped at 16 ft in height (25 ft for a converted detached garage). | There is no ongoing owner-occupancy mandate, but the owner must prove they live on the property at the time of application. UDC 7.3.304 E requires the property owner to demonstrate that the owner resides on the property when submitting an application to construct or convert an ADU, and the city implements that through a notarized Owner Residency Determination Affidavit filed with the building permit. The requirement expressly does not apply to an ADU built simultaneously with a primary dwelling. Nothing in the code requires the owner to keep living there afterward, and nothing requires either unit to be owner-occupied on an ongoing basis. This is the narrow exception Colorado's HB24-1152 leaves open: the state law bars a subject jurisdiction from requiring an ADU or any other dwelling on the lot to be owner-occupied, except that it may require the owner to demonstrate residence on the parcel when an application to construct or convert an ADU is submitted (and not for an ADU built at the same time as a new primary dwelling). Colorado Springs is on the Department of Local Affairs list of HB24-1152 subject jurisdictions. UDC 7.3.304 E (introductory paragraph); HB24-1152 sec. 29-35-103(2)(b), codified in C.R.S. article 35 of title 29 part 4 (see C.R.S. 29-35-403(2)(b))Full rules for Colorado Springs Ordinance read July 2026 | One off-street space for the ADU, in addition to the parking required for the house (2 spaces for a single-family detached dwelling). No ADU-specific waiver in the code. | Permitted use |
| Commerce City | Allowed | Allowed | 75 percent of the principal dwelling's floor area or 1,000 sq ft, whichever is less, but 750 sq ft is always allowed; detached ADU height must be less than the principal building or 22 ft, whichever is less | Not required | None. No off-street parking space is required for an ADU | Permitted use |
| Denver | Allowed | Allowed | 864 sq ft in single-unit (SU) zone districts on lots of 7,000 sq ft or less, 1,000 sq ft on larger lots; outside SU districts an attached ADU may be 75 percent of the house's floor area or 864 sq ft, whichever is greater, and a detached ADU has no floor-area cap but is limited to an 864 or 1,000 sq ft footprint and 2 stories / 24 ft | Owner occupancy is tested only in single-unit (SU) zone districts, and only at the moment the ADU permit application is filed: at least one owner of the existing primary dwelling must occupy it as their primary residence, proved by two of motor vehicle registration, driver's license, Colorado ID, voter registration, tax documents, or a utility bill. There is no continuing obligation, so once the ADU is permitted the owner may move away and both units may be rented. Two carve-outs apply: no occupancy is required when the ADU is built at the same time as a brand-new primary dwelling, and ADUs on homes owned by the Denver Housing Authority are exempt (added by the 2025 Text Amendment Mini Bundle, effective February 20, 2026). Outside SU districts there is no owner-occupancy requirement. SU-district ADUs must, however, stay under the same ownership as the primary dwelling, so the ADU cannot be sold off separately. This matches what Colorado HB24-1152 permits: C.R.S. 29-35-103(2)(b) bars a subject jurisdiction from requiring an ADU or the other dwelling on the lot to be owner-occupied, but expressly allows a jurisdiction to require the owner to show they reside on the parcel when the application is submitted. DZC §11.8.2.2.A and §11.8.2.2.B; C.R.S. §29-35-103(2)(b) (HB24-1152); D.R.M.C. §59-2(c)(21)(i)-(k), §59-2(c)(22)(a)-(b)Full rules for Denver Ordinance read July 2026 | None. Denver eliminated minimum off-street vehicle parking citywide effective August 11, 2025, so no parking space has to be added for an ADU | Permitted use |
| Durango | Detached ADUs (a unit inside an accessory building, including above a garage) are allowed in the EN-1 Old Durango, EN-2 2nd and 3rd Avenues, EN-3 East Animas City, EN-MF Multifamily, RA Rural/Agriculture, RL Residential-Low, RM Residential-Medium, RH Residential-High and MU-N Mixed-Use Neighborhood districts, and are flatly Not Allowed in EN-4 Crestview and Needham, EN-5 Riverview and EN-6 Other Single-Family Neighborhoods. The city explains that prohibition as the absence of alleys in those districts, which it treats as essential emergency-service access. Every detached ADU still needs a Limited Use Permit, must sit on the rear half of the lot in every zone except RA, must take vehicular access from an alley where one exists, and is capped by the height and setback figures in Table 2-3-2-3B. Minimum parcel areas for detached ADUs were eliminated by a Land Use and Development Code amendment that took effect 2/28/2026. LUDC Sec. 2-3-2-3.C and Table 2-3-2-3A, Zones and ADU Types; Sec. 2-3-2-3.B.2, H and I.2Full rules for Durango Ordinance read July 2026 | Allowed | 550 sq ft (basement ADUs exempt) | Required | 1 off-street space for the ADU (2 total if the lot has none); 1-space reduction possible near qualifying on-street parking | An ADU is a 'major accessory use' that requires a Limited Use Permit before construction. Durango's Limited Use Permit is administrative: Table 6-3-2-2 lists it as issued by the Administrator, and Sec. 6-3-2-2.A states administrative approvals are issued without a requirement for a public hearing, with the decision due within 30 calendar days of a complete application. It is nonetheless discretionary rather than by right, which is why this field is not marked 'permitted': under Sec. 2-2-2-1 staff must find the ADU will not conflict with adopted City plans and is compatible with surrounding land uses and the character of the immediate area. The application triggers a 14-day notice posted on the property and mailed notice to owners within 300 feet, both starting five days after the application is complete, plus a 15-day public comment period. A pre-application meeting is required, the fee schedule is set by the city, and staff decisions may be appealed under Division 6-3-17. A building permit is separately required for any structure 120 square feet or larger. LUDC Sec. 2-3-2-3.A; Sec. 2-2-2-1; Sec. 6-3-2-2.A and Table 6-3-2-2; Sec. 6-3-3-9.C.1.d; Sec. 6-3-3-10 Table 6-3-3-10B; Sec. 6-3-3-11 Table 6-3-3-11Full rules for Durango Ordinance read July 2026 |
| Fort Collins | Allowed | Allowed | Detached: 750 sq ft if the primary building is under 1,667 sq ft, otherwise 1,000 sq ft or 45 percent of the primary dwelling, whichever is less; 800 sq ft of habitable space when converting an accessory structure that was legal when the LUC was adopted. Attached: the greater of 750 sq ft or 45 percent of the primary dwelling at or above grade, the greater of 750 sq ft or 100 percent of the floor level below grade. Detached height 1.5 stories / 28 ft. | Not required | None for the ADU itself; the lot only has to meet the parking minimum for its primary dwelling | Permitted use |
| Golden | Allowed | Allowed | 800 sq ft or 50 percent of the principal dwelling's living space, whichever is smaller; 500 sq ft cap if the main home has under 1,000 sq ft; 200 sq ft minimum | Required | One on-site space for the ADU, on top of the parking required for the main house; tandem allowed but must be shown on a site plan | Permitted use |
| Grand Junction | Allowed | Allowed | 900 sq ft of habitable space per ADU | Not required | None; no off-street parking is required for an ADU | Permitted use |
| Greeley | Allowed | Allowed | 60 percent of the principal dwelling's living area or 1,200 sq ft, whichever is less | Not required | 1 off-street space per bedroom under the codified table; state law now bars most new-space mandates for ADUs | Permitted use |
| Jefferson County | Allowed | Allowed | Attached: 1,200 sq ft or 40 percent of the primary unit, whichever is less (basement conversions exempt from that cap). Detached: 1,200 sq ft on lots of 1 acre or more, 800 sq ft on lots of 12,500 sq ft or more, 600 sq ft on lots of 7,500 sq ft or more, each also capped at 40 percent of the primary unit. Any ADU may be at least 500 sq ft regardless of the percentage. | Required | One additional off-street space for each bedroom in the ADU, so one or two spaces, since an ADU is capped at two bedrooms | Permitted use |
| Lakewood | Allowed | Allowed | 1,400 sq ft gross floor area; height capped at 20 ft, or 30 ft if over a detached garage | Section 17.4.3.1:A(4) provides that a permit for an ADU shall only be issued to an owner occupant or their designee, so the city tests owner occupancy at the time the ADU is permitted. Colorado's ADU law bars a subject jurisdiction from requiring an ADU, or any other dwelling on the same lot, to be owner-occupied, but expressly allows the jurisdiction to require the owner to demonstrate that they reside on the parcel when the application to construct or convert is submitted, so Lakewood's permit-stage rule falls within that exception. Nothing in the code imposes a continuing owner-occupancy condition, and the state law means none can be enforced after the permit issues: an owner may move out and rent both units long term. The state exception does not apply at all where the ADU is built at the same time as a new primary dwelling. Ordinance read July 2026 | None unless on-street parking is unavailable, in which case 1 off-street space | Permitted use |
| Longmont | Allowed | Allowed | 500 to 800 sq ft by right regardless of house size; larger allowed if within 50 percent of the principal dwelling's finished above-ground floor area; basement ADUs have no size cap | Not required | None required; an ADU may add at most two off-street spaces | Permitted use |
| Loveland | Allowed | Allowed | 900 sq ft maximum floor area; on Large Suburban, Estate and Large Estate lots an ADU may exceed 900 sq ft up to 50 percent of the principal dwelling's floor area | Not required | None. Off-street parking is not required for an ADU | Permitted use |
| Monument | Allowed | Allowed | 50 percent of the principal structure's floor area or 750 sq ft, whichever is greater; Large Lot Residential District up to 1,250 sq ft; no ADU smaller than 500 sq ft. Detached ADUs limited to 16 ft in height (25 ft for a converted garage); attached ADUs to the district maximum but never above 25 ft. | Monument requires the property owner to demonstrate that the owner resides on the parcel at the time an application to construct or convert an ADU is submitted. That requirement does not apply when the ADU is being built at the same time as a new primary dwelling. The provision is copied from the narrow carve-out Colorado allows in C.R.S. 29-35-403(2)(b), which otherwise forbids a subject jurisdiction from requiring an ADU, or any other dwelling on the same lot, to be owner-occupied. So there is no continuing owner-occupancy condition: once the ADU is permitted and built, the owner may move away and rent out both units on a long-term basis. Ordinance No. 17-2026 left this subsection unchanged. Separately, the Town's fifty percent use tax rebate for low- and moderate-income ADUs requires the applicant to own and reside on the property when the rebate application is submitted. Monument Municipal Code Sec. 18.03.340.D.4.h and .D.5.b.ii; C.R.S. Sec. 29-35-403(2)(b)Full rules for Monument Ordinance read July 2026 | None in most cases: no additional off-street space is required, unless the lot has no existing off-street space AND is on a block where on-street parking is prohibited AND is in a district that requires parking for the principal dwelling, in which case one space is required. | Permitted use |
| Parker | Not allowed | Not allowed | No ADU size cap exists because ADUs are prohibited in every district. The only accessory living space Parker allows, one basement Secondary Family Space per home, may not exceed 40 percent of the main dwelling unit including the basement, measured on the original square footage of the single-family detached dwelling as initially constructed. | Required | None, because there is nothing to park for. Table 13.08.F assigns 'N/A' to 'Dwelling Unit, Accessory' in both parking columns, and the table's own key defines 'N/A = Not Applicable (Prohibited Use in Zoning District).' A single-family detached dwelling requires 2 spaces per dwelling unit, and a basement Secondary Family Space is not listed in Table 13.08.F and triggers no additional space. | There is no ADU approval pathway of any kind, so none of the permitted, conditional-use or varies categories applies. Table 13.05.A shows 'Dwelling Unit, Accessory' as 'Not permitted' across every district; Section 13.05.020(a)(3) states that 'A blank cell indicates that the use is prohibited in the respective zoning district'; and Section 13.05.020(b) adds that 'All other uses not specifically listed are prohibited unless the Planning Director has determined an appropriate use type for the unlisted use.' The only adjacent permit is an administrative building permit from the Parker Building Division for a basement Secondary Family Space, which Table 13.05.A treats as an accessory use by right (A+) in SF1, SF2, SF3 and AG and which issues once the recorded declaration of restrictions is in hand; no Planning Commission or Town Council hearing is involved. Had Parker complied with C.R.S. 29-35-403(1), an ADU application would have had to be decided through an administrative approval process against objective standards only, with no public hearing. LDO Sec. 13.05.020(a)(3), Sec. 13.05.020(b) and Table 13.05.A; Sec. 13.05.050(d)(1); PMC Sec. 11.02.050(10) item 3; C.R.S. 29-35-403(1)Full rules for Parker Ordinance read July 2026 |
| Pueblo | Allowed | Allowed | Lesser of 800 sq ft or 100 percent of the house's gross floor area | Not required | None in most cases; 1 space only if the lot has no usable off-street space and on-street parking is banned on that block | Permitted use |
| Thornton | Allowed | Allowed | 1,000 sq ft or 50 percent of the primary dwelling's gross floor area, whichever is greater (garage and porch areas excluded) | Required | 1 off-street space per ADU on the same lot, in addition to the 2 spaces required for the main house | Permitted use |
| Westminster | Allowed | Allowed | Lesser of 1,200 sq ft or 50 percent of the home's gross floor area; homes under 1,500 sq ft may host an ADU up to 750 sq ft; 190 sq ft minimum; two bedrooms max | Not required | None in most cases; one new space only if the lot has no usable existing off-street space and on-street parking is prohibited on the block | Permitted use |
Summarized from each city's ordinance text, most recently read July 2026. Tap a value marked with an info icon to see exactly what it depends on, straight from the ordinance. Nearly every value has zone, lot-size, or process caveats beyond that; the per-city pages carry the full notes and code citations. Treat this as orientation, not a permit determination.
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Reading the table
- Detached ADU is the make-or-break column for backyard cottages: minimum lot sizes (often 8,000 to 14,500 sq ft) hide behind many of the "Allowed" values, so check your lot before celebrating.
- Attached / internal (basement apartments, additions) is legal almost everywhere and is usually the path of least resistance.
- Approval: "Permitted use" means staff-level sign-off; "Conditional use" means a public hearing, which adds time, cost, and uncertainty.
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