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Accessory Dwelling Units (ADU)

Accessory Dwelling Units (ADU)

Online Feedback Results

Be Heard Boulder, the city's new online engagement platform, was used to gather opinions on the proposed recommendations to ADU regulations. View the results here pdf.


City Council responded to community requests to encourage the creation of new Accessory Dwelling Units (ADUs) by requesting that staff bring forward a list of incremental changes to city regulations that better allow accessory units while still addressing potential neighborhood impacts. Council has identified this as a work plan item for the past several years. On Aug. 22, staff presented council with a list of potential regulatory changes that would remove some of the barriers to creating accessory units, including but not limited to, addressing standards regarding unit concentration, sizes, and parking. The project will include incremental and focused changes to the regulations, not wholesale changes.

What is an Accessory Dwelling Unit?​

Often called an “in-law apartment” or “garage flat”, accessory dwelling units are a separate and complete housekeeping unit (e.g., kitchen, sleeping area and bathrooms) that is either attached or detached from the primary residential unit on a single-family lot. There are primarily two types of accessory dwelling units defined in the regulations:​

  1. Accessory Dwelling Unit (ADU) – typically within a single-family detached dwelling unit​.
  2. Owner Accessory Unit (OAU) – typically attached to a single-family dwelling unit or located in an accessory building​.

Click for the full diagram.

Where are ADUs Today?

The construction of accessory units are reviewed by  the city through an administrative process.

A summary of current  regulations and a guide to  the application and review process  is available here pdf

ADU Map - 2017

Map of ADUs in Boulder from 2012

Click Map for the full view.

Where are ADUs Allowed?

Allowed Zone Map for ADUs

Zone map for allowed ADUs

Click Map for the full view.

Allowed Zone Map for OAUs

Zone Map for allowed OAUs

Click Map for the full view.


Accessory Dwelling Unit Survey 2017

A new ADU survey was sent to the 230 owners of accessory units in Boulder to update the 2012 study. The 2017 survey response rate was 70 percent and includes a comparison of the 2012 and 2017 results. The full report is available here pdf, and a summary of key findings is below:

Key Findings 2017 Survey

  • For most respondents (74 percent), supplemental income through rental of the ADU was the reason they had created or retained the ADU and also supplemental income was also seen as the primary benefit.
  • When asked if they had noticed an increase in their property taxes after building their ADU, 20 percent said they noticed a large one and 18 percent said they noticed a small increase. About 30 percent said they had not really noticed an increase, and 33 percent could not remember.
  • When respondents were able to make an estimate of the annual household income of their ADU tenants:
  • 35 percent were estimated to have incomes of less than $40,000;
  • 40 percent were between $40,000 to $80,000; and
  • 25 percent were more than $80,000.
  • Overall, about 1 percent of ADU owners reported receiving occasional complaints about their unit from their neighbors. When examined by type of unit, OAU owners received zero occasional complaints, while 1 percent of ADU owners reported receiving occasional complaints.

 Read the full report is available here pdf,


Current Uses for ADUs

ADU Usage Pie Chart Graphic - Long-Term 64%, Short-term 11%, For Visitors 6%, Other 5%, For Relatives 5%, Owner Occupied and rents out main 4%, Extra Space 3%, Rental in exchange 1%


Ages of ADU Occupants

Ages of ADU Occupants - Not Occupied or Rented, 19%; 1 or more under 18, 4%; 1 or more 18-29, 36%; 1 or more 30-65, 59% and 1 or more 65 plus, 11%


Community Engagement - Project Milestones

1. Launch Community Engagement and Complete Foundations Work. Oct - Dec 2017

Create a community engagement plan pdf that meets Council and Planning Board expectations for an incremental change to the regulations related to accessory units. The initial engagement will focus on getting community feedback on the draft WHY and PURPOSE statements and the draft list of focused code changes – prior to crafting a specific proposal.

  • Clearly articulate and communicate the scope of this effort and what is not getting addressed.

  • Reinforce the incremental nature, rather than whole sale change.

  • Clearly identify project milestones where community input into the process is most effective.

  • Conduct additional qualitative and quantitative analysis to update and support the 2012 ADU Study.  The information will be used to understand how neighbors of existing ADUs perceive impacts from the units.

  • Continue to explore options for ensuring ADUs are affordable (either through covenants, voluntary agreements, or incentives such as fee waivers).

  • Community Outreach in October/November 2017 – Planning Board meeting to seek input prior to public meetings on the following: discussion of DRAFT why statement, DRAFT purpose statement, and the draft list of focused code changes.

  • Hold 2 separate open houses in November (North and South Boulder) to request input on the above. Open house will include posters on background materials, draft why and purpose statement.

  • Create the opportunity for attendees to share their ADU story (written or video).

  • Explore opportunities to combine outreach efforts with the Building Height project.

  • Issue an open invitation to meet with any stakeholder.

Deliverables: Detailed project schedule; community engagement plan; final why and purpose statements; draft list of focused code changes; Planning Board meeting; project website and project launch press release.

2. Community Discussion Draft Proposal. January - February 2018

Based on community and board input from previous engagement, publish a discussion draft of a staff report that identifies barriers and details potential changes to the ordinance. This will include additional analysis and data collection to support the discussion draft and a summary of community engagement activities and input to date.

  • Community Outreach in – review of discussion draft. Hold 3-5 separate open houses in January (North, Central, East and South Boulder) to request input.

  • Conduct targeted outreach (coffee talks, office hours, meetings with stakeholders, etc.)

  • Coordinate outreach with the Building Height project.

  • Issue an open invitation to meet with any stakeholder.

Deliverables: Discussion Draft Proposal; survey results

3. Planning Board and Council Public Hearings. Mar - Apr 2018

Based on community input, publish a Planning Board memo with a staff recommendation for a final round of community events to inform the public hearings with Planning Board and City Council. Included in the recommendation will be a summary of community input and how that input shaped the contents of the proposal.

Community Outreach – public hearings with the Planning Board and City Council. Deliverables: Planning Board and Council memos; Adopted Accessory Dwelling Unit ordinance.

Deliverables: Planning Board and Council memos; Adopted Accessory Dwelling Unit ordinance.

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