ADU rules in Arvada

A detached backyard ADU (the city calls it a Type A ADU) is allowed on any lot with a single-family detached house in Arvada's residential districts (RA, RN, R6, R13, R24), the Olde Town (OT) districts and the mixed-use (MX) districts. Only one ADU is allowed per residential lot, and the principal single-family detached house must already exist or be built at the same time as the ADU. On interior lots a Type A ADU must sit at or behind the front plane of the main house; on corner lots it must be at least ten feet behind the facade of the main house along both street frontages.

An internal or attached ADU (the city calls it a Type B ADU) is allowed in the same districts. Type B covers a unit created in a basement or upper story, or attached to the principal single-family detached building, where the ADU occupants and the main household do not live together as one household. Both types count as separate dwelling units under the building code, so fire separation from the main house and a separate HVAC system are required, and water and sewer must connect to the main house's service lines rather than to new taps.

For a newly built detached ADU or a new addition, both tests apply and the smaller number governs: no more than 40 percent of the living space of the principal building (garages, unfinished basements and patios do not count as living space), and no more than the Table 5-1-5-2 figure for your lot size. Conversions that stay within the footprint of an existing home, such as a basement unit, escape both limits and are capped only at 50 percent of the principal dwelling's floor area including the basement. Every ADU must be configured as a studio, one-bedroom or two-bedroom unit, and garage space built for the ADU occupants may not exceed 250 sq ft.

Arvada's adopted code still requires it: the property owner of record must occupy either the main house or the ADU, and before a building permit is issued the owner must record a deed restriction with the Jefferson County Clerk and Recorder stating that the ADU's certificate of occupancy is effective only while the owner lives in one of the two units. The Director may waive the requirement for a temporary absence of under one year if the use has been maintained for at least two years. However, Colorado's HB24-1152 (C.R.S. 29-35-403(2)(b)) bars a subject jurisdiction from requiring an ADU, or any other dwelling on the same lot, to be owner-occupied on or after June 30, 2025, and the state Division of Local Government lists Arvada as a subject jurisdiction. Arvada has not amended Sec. 5-1-5-2 since 2022, so this local mandate is very likely unenforceable; confirm current practice with Arvada Planning before relying on either reading.

Sec. 5-1-5-2.D requires one on-site space for the ADU in addition to any space required for the principal dwelling, and expressly allows that space to be in tandem with other required spaces (for example stacked in a driveway), so a new curb cut or garage is not needed. Garage space built for the ADU occupants may not exceed 250 sq ft. Note that HB24-1152 (C.R.S. 29-35-403(2)(a) and (3)) lets a subject jurisdiction require only that an existing driveway, garage or tandem space be designated for the ADU, and permits a required new space only on a narrow set of lots with no existing off-street parking and no on-street parking; Arvada's text has not been updated to track that limit.

By right with administrative review only. ADUs are an accessory use allowed under Sec. 5-1-5-2 with no conditional use, no rezoning and no public hearing, and Table 8-2-2-2B expressly lists 'Accessory dwelling units and accessory buildings' as an exception to the Site Plan requirement, so no site plan application is filed. The approval is a building permit submitted through the city's online permitting system (Arvada Permits / eTRAKiT), reviewed by staff for zoning and building compliance; the city advertises about three weeks of review for a detached Type A ADU and one to two weeks for a Type B. Permits are issued only to contractors holding a City of Arvada type 1B, 2B or 3B license, and the deed restriction must be recorded before the permit issues.

Renting an ADU for 30 or more days needs no city permit; the code itself says a Type B ADU is typically rented. The recorded deed restriction bars selling the ADU separately from the main house and keeps the ADU's certificate of occupancy alive only while the owner occupies one of the units. For stays under 30 days Arvada rewrote its STR rules in Ordinance No. 4917, adopted February 17, 2026 and effective May 1, 2026: an STR permit plus a city business license are required; the permit may be issued only to one natural person holding at least a 20 percent ownership interest; no person may hold more than three permits citywide; only one STR permit is issued per lot, so the city's FAQ confirms that only the ADU or the primary structure can be the permitted STR; stays must be at least two consecutive nights; guest occupancy is capped at 240 days per 365; one additional on-site parking space is required unless the entire premises is rented; an annual inspection by a certified home inspector, an emergency contact available within one hour, smoke and CO detectors and a fire extinguisher are required; and lodging plus sales taxes must be remitted. Deed-restricted or affordable-designated dwellings may not be used as STRs. HB24-1152 expressly preserves local authority to regulate short-term rentals of ADUs, so these rules stand.