ADU rules in Denver

Denver allows one accessory dwelling unit on every zone lot with a single unit, two unit, or multi-unit dwelling, and a detached backyard cottage or carriage house is the standard form. The Citywide ADUs text amendment, passed November 18, 2024 and effective December 16, 2024, extended the ADU use to all residential zone districts, and the accessory use tables in Articles 3 through 9 of the Denver Zoning Code now list Accessory Dwelling Unit as 'L-ZP' (permitted with limitations, zoning permit review) in every Suburban, Urban Edge, Urban, General Urban, Urban Center, Downtown, Master Planned, and industrial mixed use district. Properties still zoned under Former Chapter 59 are covered too: D.R.M.C. Sec. 59-2(c)(19) permits one ADU accessory to each single unit dwelling in every Former Chapter 59 district that allows new single unit dwellings. A detached ADU must sit in the rear part of the lot (rear 50 percent of lot depth in Suburban S- districts, rear 35 percent in Urban Edge and Urban districts).

An attached or internal ADU (a basement apartment, an attic conversion, or an addition) is allowed wherever the primary use is a single unit dwelling: the maximum gross floor area table in DZC 11.8.2.1.B.2 expressly covers ADUs located 'Attached or Detached' in SU zone districts and 'Attached' in all other districts. The one limit is that an ADU accessory to a two unit, row house, or town house primary use must be built in a detached accessory structure and is not allowed inside the primary structure. Only one kitchen per ADU is allowed, and the unit may start with a partial kitchen and later convert to a full kitchen. An attached ADU may have its own outside stairway, but not on a street-facing facade of the main house.

The size rules split by zone district. In every SU (single unit) district the ADU's gross floor area may not exceed 864 sq ft on a zone lot of 7,000 sq ft or less, or 1,000 sq ft on a larger lot, whether the unit is attached or detached. Outside SU districts, an attached ADU may be the greater of 75 percent of the primary dwelling's gross floor area or 864 sq ft, and a detached ADU has no gross floor area cap at all. Detached units are instead bounded by the Detached Accessory Dwelling Unit building form: a maximum footprint of 864 sq ft per unit on lots of 7,000 sq ft or less and 1,000 sq ft on larger lots, and a height cap of 2 stories and 24 ft (in S-SU and E-SU districts a one-story option is capped at 17 ft in exchange for a smaller rear setback). Former Chapter 59 properties use the same 864 and 1,000 sq ft caps in the RS-4, R-X, R-0, R-1, R-2, R-2-A and R-2-B districts, with a 24 ft height cap.

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.

Denver's Modernizing Parking Requirements text amendment took effect August 11, 2025 and deleted minimum vehicle parking from both the Denver Zoning Code and Former Chapter 59 zoning. Division 10.4 of the code now contains only maximum vehicle parking limits (near rail stations and in the D-CPV districts), minimum bicycle parking, and design rules; there is no minimum vehicle parking table left. Sections 10.4.2.3 and 10.4.2.4 go further and bar the Manager from enforcing minimum parking written into an approved regulating plan, site development plan, zoning permit, PUD, or zone district with waivers. Bicycle parking minimums do not reach ADUs either: the table in 10.4.3.5 shows 'No requirement' for single unit and two unit dwellings. What does still apply is vehicle access: a detached ADU must take access from the alley where one exists, and the ADU may not have a driveway separate from the one serving the main house except for new alley access.

An ADU is a permitted accessory use approved administratively. The use tables in Articles 3 through 9 mark Accessory Dwelling Unit as 'L-ZP', meaning permitted with limitations and subject to zoning permit review under DZC 12.4.1: the Zoning Administrator makes the final decision against fixed criteria (consistency with prior approvals and compliance with the code), with no public hearing, no neighbor notice, and no community information meeting. In practice a homeowner files for zoning, building, and sewer use and drainage permits together (they can be reviewed simultaneously), plus trade permits, and needs a Certificate of Occupancy before anyone moves in. Denver requires ADUs to be built by a licensed contractor; the city's ADU permitting page states homeowners cannot apply for ADU permits themselves. Landmark structures and properties inside historic districts additionally need a certificate of appropriateness from Landmark Preservation, and PUD-zoned properties are handled under DZC 11.8.2.3.

Renting an ADU for 30 days or more is allowed, but Denver licenses it: D.R.M.C. 27-192(6) defines a residential rental property to include an accessory dwelling unit offered for rent as a residence, and since January 1, 2024 a license has been required even for a single rented dwelling unit on a parcel, which brings a periodic inspection and minimum housing standards. Short-term rentals of under 30 days need a separate license from the Department of Excise and Licenses, and it is unlawful to operate one anywhere that is not the applicant's primary residence. For ADUs the zoning code draws the line precisely: if you live in the main house you may short-term rent either the main house or the ADU, but not both at the same time; if your primary residence is the ADU, you may not operate a short-term rental at all. Advertisements must display the license number, and lodger's tax applies. Colorado HB24-1152 expressly leaves these local short-term rental rules intact for ADUs.