Douglas County approves zoning amendment to allow accessory dwelling units

The Douglas County Board of County Commissioners on June 24 approved amendments to the county zoning resolution to allow accessory dwelling units, or ADUs, in several residential zoning districts and to add a formal ADU definition (project file DOCTOR2024-001).

Staff said the change defines ADUs (including guest houses), allows attached ADUs in SR (suburban residential), ER (estate residential), RR (rural residential), LRR (large rural residential) and A-1 (agricultural) zone districts, and sets minimum lot sizes for detached ADUs: 1 acre where a lot is served by central water and septic, and 2 acres where a lot is served by a private groundwater well and septic. Detached ADUs in SR are permitted on lots greater than 0.5 acre. The amendment would permit up to two ADUs on A-1 lots of at least 35 acres, with the second ADU subject to additional board review and approval.

The ADU proposal was prepared by Planning Resources staff, forwarded to referral agencies for comment and heard by the Planning Commission on June 16, 2025. Staff reported that most referral agencies provided no comment or no objection, while several homeowners associations — including Burning Tree Ranch HOA, Deerfield Community, Grandview Estates HOA, Happy Canyon HOA and Parker View Estates HOA — submitted letters urging the board to pause or discontinue the amendment, citing concerns about density, impacts to rural character, groundwater, traffic and enforcement of HOA covenants. A public workshop held Dec. 13, 2024 drew 13 attendees from Franktown, Parker and Roxborough-area communities, staff said.

At the Planning Commission hearing three members of the public spoke in opposition, and the Planning Commission recommended denial by a 5–0 vote, stating the amendment would increase density in ways the commission viewed as contrary to the comprehensive master plan. In the commission and referral comments staff was asked to perform broader outreach and provide additional detail on enforcement and water impacts.

During the Board of County Commissioners discussion, one resident, Tom Bowles of the Franktown/Deerfield area, said the measure would "commercialize residential areas" and voiced opposition to what he called increased density and short-term rental use. Planning staff responded with the proposal's technical limits and the definition language, and commissioners debated competing priorities of private property rights, rural preservation and limited local water resources. Several commissioners said they had moved from initial skepticism to support after reviewing draft language and limits (for example, minimum-lot thresholds and exclusion of planned developments).

After discussion a commissioner moved to approve the resolution adopting amendments to Section 3 (A-1), Section 4 (LRR), Section 5 (RR), Section 6 (ER), Section 7 (SR) and Section 36 (definitions) of the Douglas County Zoning Resolution (project file DOCTOR2024-001); another commissioner seconded. The board voted in favor; the motion carried unanimously.

The adopted changes add a formal ADU definition, allow attached ADUs in the enumerated zones, permit detached ADUs subject to minimum lot sizes tied to water supply, and permit an additional ADU on large A-1 parcels subject to board review. Staff retained that ADUs remain accessory to a principal dwelling and that the rules do not enable lot subdivision.

The board may still act to modify, table for further study, remand to the Planning Commission or otherwise revise the regulation in a future meeting; the adopted resolution represents the board's action on this proposal at the June 24 public hearing.