ADU rules in 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.

Aurora's code flatly prohibits attached and internal ADUs: UDO §146-3.3.6.G.1.d states that each accessory dwelling unit must be detached from the primary dwelling and that attached accessory dwelling units are not permitted. Basement apartments and additions therefore cannot be permitted as ADUs under the codified ordinance anywhere in the city. State law defines an ADU as an internal, attached, or detached unit, and both the compliance ordinance the council rejected in June 2025 and the draft ordinance the council directed staff to prepare at its July 13, 2026 study session would allow internal, attached, and detached ADUs, but neither is adopted law as of July 31, 2026.

The maximum size of an accessory dwelling unit is 650 square feet, and the unit may not exceed 24 feet in height regardless of the primary dwelling's height (an older clause in the same subsection also ties height to the principal dwelling or 24 feet, whichever is less). The lot must additionally provide at least 360 square feet of usable private common space for the ADU with no dimension under 10 feet. Note that under HB24-1152 a standard that does not allow ADU sizes between 500 and 750 square feet is a prohibited restrictive dimension standard for subject jurisdictions; Aurora's 650-square-foot cap predates the state law and had not been amended as of July 31, 2026.

The codified UDO requires the property owner to occupy either the primary dwelling unit or the accessory dwelling (§146-3.3.6.G.1.l). Since June 30, 2025, HB24-1152 (C.R.S. 29-35-403(2)(b)) has prohibited subject jurisdictions like Aurora from requiring an ADU or any other dwelling on the same lot to be owner-occupied; a city may only require proof that the owner resides on the parcel at the time of an application to build or convert an ADU, or for a short-term rental license. Aurora has not amended the UDO, so the local owner-occupancy mandate conflicts with state law. Separately, Aurora's short-term rental code independently requires any STR to be the operator's primary residence.

For the ADUs the code allows (alley-served Original Aurora lots), UDO §146-3.3.6.G.1.k requires one additional off-street parking space accessed from the alley serving the lot. Since June 30, 2025, HB24-1152 (C.R.S. 29-35-403(2)(a) and (3)(a)-(b)) has barred subject jurisdictions from requiring construction of a new off-street space for an ADU except on parcels that have no usable existing off-street space, are in a district that required parking for the primary home as of January 1, 2024, and are on a block where on-street parking is prohibited; a city may still require designating an existing space. Aurora's parking standard predates the act and had not been amended as of July 31, 2026.

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.

Nothing in the UDO bars renting an ADU on ordinary month-or-longer leases, but because the owner must occupy either the primary home or the ADU, only one of the two units can be rented out. Short-term rental is narrower: UDO §146-3.3.6.G.1.n allows an ADU to be used as a short-term rental only by a property owner who is living in the primary structure. Citywide STR rules in City Code §§26-215 to 26-220 require a general business license and lodger's license before advertising, require the dwelling to be the operator's primary residence, cap whole-dwelling rentals at 180 days in any 365-day period, and allow only one booking at a time, though ADUs are exempt from the one-booking rule when the owner lives in the primary structure. An 8 percent city lodger's tax applies to stays under 30 days.