ADU rules in Castle Rock

The ADU definition expressly includes a detached structure on the same lot or tract as the primary dwelling, and Section 17.61.040.C allows ADUs in all residential zone districts (R-1, R-2, R-3) and in any Planned Development (PD) area designated for single-family residential uses, subject only to administrative review by the Director of Development Services and a building permit. Because most Castle Rock neighborhoods are zoned PD, Ord. 2025-023 (July 1, 2025, the town's HB24-1152 alignment ordinance) added Section 17.61.020.B making Chapter 17.61 govern over any conflicting PD zoning regulations for ADUs accessory to single-unit detached homes, with the more permissive provision controlling. ADUs are prohibited in the MH Manufactured Home district and on residentially zoned lots containing an existing or proposed duplex, triplex, condominium, townhome, or multifamily dwelling.

The ADU definition covers a unit located within, but physically separated from, an existing primary dwelling (including an attached garage) and an addition to the primary dwelling that is physically separated from it, so basement finishes, garage conversions, and additions all qualify. Physical separation may be a wall, a wall with a door, or a similar feature; a door frame, door hinges, a pocket, or an opening of 38 inches or less in width constitutes separation. Approval follows the same administrative building-permit path as detached units, and the town's ADU application lists basement finish and residential remodel as standard ADU types.

An ADU located inside the primary dwelling, whether as part of it or as an addition, may not exceed 50 percent of the primary dwelling's floor area or 750 square feet, whichever is greater. A detached ADU may not exceed an 800 square foot building footprint attributable to the ADU, unless the lot's PD zoning regulations set a more permissive size limit, in which case the PD standard governs. The cap on a detached unit is written as a footprint limit rather than total floor area. District or PD zoning regulations for the construction and placement of structures (height, coverage) otherwise apply, and side and rear setbacks follow accessory-structure standards with state-law-compliant caps.

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).

The ADU chapter's building-permit conditions (Section 17.61.050.C) contain no off-street parking requirement, and the town's ADU application collects no parking information. The general parking table (Table 64-1 in Section 17.54.040) requires 2 off-street spaces per dwelling unit for the single-family residence itself and has no ADU category. Since June 30, 2025, C.R.S. 29-35-103(2)(a), enacted by HB24-1152, prohibits Castle Rock, a subject jurisdiction, from requiring construction of a new off-street parking space for an ADU; the narrow state exceptions (designating an existing space, or one new space on a lot with no existing off-street parking in a district that required parking as of January 1, 2024 and where on-street parking is banned on the block) are not implemented as ADU conditions in the code.

ADUs are approved administratively in every location where they are allowed: Section 17.61.040.C permits them in all residential zone districts and in PD areas designated for single-family residential uses upon an administrative review by the Director of Development Services and approval of a building permit. No public hearing, special review, or conditional use approval applies; the one-page ADU application is filed with the Building Division together with the building permit. A request to deviate from the ADU standards to install accessibility features for disabled persons goes to the Board of Adjustment under Chapter 17.06.

The current code places no restriction on long-term rental of the ADU or the primary dwelling. Ord. 2025-023 (July 1, 2025) repealed the prior Ord. 2023-007 rule that prohibited both units from being renter-occupied at the same time and required a recorded deed restriction to that effect, so both units may now be rented; the ADU may never be subdivided or sold separately from the primary home. Castle Rock has no short-term rental licensing program: the town's official FAQ (crgov.com/faq.aspx?qid=742, information as of Dec. 20, 2023) states the town does not regulate short term rentals such as Airbnb or VRBO, though operators need a town business license and must collect and remit lodging and sales taxes. Section 17.61.050.C.3 expressly reserves the town's authority to adopt ADU short-term rental regulations in the future, and a code-wide search confirms no STR chapter exists as of Supp. 63 (June 2026).