Accessory Dwelling Unit Updates

City Council approved updates to the Accessory Dwelling Unit regulations in the land use code in May 2023. These changes apply to any ADU proposed on or after Sept. 1, 2023.

An accessory dwelling unit, also known as an “in-law apartment” or “garage flat” or “ADU,” is an additional living unit that has separate kitchen, sleeping and bathroom facilities, attached or detached from the primary residential unit on a single-family lot. The first ordinance allowing accessory dwelling units in Boulder was adopted in 1983. The regulations have been updated over time, with the most recent updates adopted in 2018.

Accessory dwelling units have been discussed as one tool to address Boulder’s housing challenges over the past decade or more to help provide “a diversity of housing types and price ranges,” which is a core value of the Boulder Valley Comprehensive Plan. The current regulations limit the percentage of ADUs within a certain radius in some zoning districts (a “saturation limit”) and establishes a waiting list for properties that are in areas that have reached their saturation limit.

In 2022, city staff completed an evaluation to understand how the 2018 changes had impacted the development of ADUs in the city, and what barriers for ADUs might remain in the land use code. The saturation limit, floor area requirements, and general code clarification and process improvements were identified as key issues to address.

• 2022 ADU Evaluation (PDF)