The Boulder City Council may consider new rules that make it easier to build ADUs in Boulder's single-family home neighborhoods, such as Mapleton Hill. Credit: John Herrick

The City of Boulder’s Housing Advisory Board wants the city to enact new rules that make it easier for homeowners to turn their basements, garages or backyards into an accessory dwelling unit, or ADU. 

The five-member panel on Wednesday, Oct. 26, released its recommendations urging the Boulder City Council to eliminate some of the biggest obstacles to building ADUs — including requirements that owners must provide off-street parking and saturation limits on how many can be built in neighborhoods. 

In January, the council made it one of its priorities to revise the city’s ADU regulations to help address the city’s housing supply crisis. Councilmembers are scheduled to begin discussing potential reforms as soon as November. 

ADUs — also known as granny flats, backyard cottages or in-law apartments — are typically rented out for extra income or used for family and friends. 

The city’s approximate 480 ADUs account for about 1% of its total housing stock. Adding more of these relatively affordable homes, which are built primarily in single-family home neighborhoods, are an incremental step toward addressing the housing crisis. 

The average rent for a market-rate ADU is $1,626 per month, city officials told Boulder Reporting Lab. In exchange for a more lax permitting process, homeowners can build an “affordable” ADU. This means rent and utilities are capped so that people earning up to 75% the city’s area median income ($89,000) spend no more than a third of their income on housing. For a studio-style, zero-bedroom affordable ADU, the cost of rent and utilities is limited to $1,646, according to the city. Renters do not need to meet income qualifications. 

The most controversial change recommennded by the Housing Advisory Board is to eliminate off-street parking requirements for building new ADUs. Credit: John Herrick

The recommendations  

Most of the recommendations were first drafted by a group of housing advocates and former councilmembers who, in September 2022, wrote a letter to the Housing Advisory Board arguing such reforms could “improve the availability and affordability of housing in Boulder.”

City survey data indicates most Boulder residents support ADUs. But the effort to potentially bring more cars and people into single-family home neighborhoods is almost always controversial in Boulder, stoking longstanding tensions around crowds, urban density and neighborhood character. 

The most controversial change suggested by the Housing Advisory Board is to eliminate parking requirements. 

Under existing rules, homeowners seeking to build a market-rate ADU must provide one off-street parking spot. The parking minimums have long been a hurdle to building an ADU. It’s one of the primary reasons some residents opt to build affordable ADUs, which do not require off-street parking, according to city survey data. 

The interest in nixing the requirement comes as cities across the country eliminate parking minimums for new buildings and as housing advocates push back against car culture in favor of more public transit and walking and cycling infrastructure.

“I would love to see a lot more opportunities for people to live car-light lifestyles, and denser neighborhoods where they’re not required,” Housing Advisory Board member Philip Ogren, a computer scientist and local housing density advocate, said during a Sept. 28, 2022 meeting. 

Also on the chopping block are saturation limits, a policy aimed at capping the density of ADUs in neighborhoods. Generally, residents cannot build an ADU if 20% of the housing units within a 300-foot radius of their property already have them. City officials have studied ADU policies in 36 other “comparable” cities. Boulder is the only one with saturation limits, according to a recent presentation

In 2018, the Boulder City Council lifted saturation limits to 20% from 10%. Since then, the city has approved about 200 ADU permits. Just 15 are on the waiting list for approval because their neighborhoods are saturated, according to city data. 

While the data suggests saturation limits may not be the biggest impediment to new ADU construction, they are a perceived barrier that may be preventing people from even trying to build one in the first place. City officials said some residents have raised concerns about paying the $420 ADU administrative review fee only to find out they might not be allowed to build. 

“It’s very challenging for people to get past that first barrier in understanding whether they can build an ADU on their property,” Lisa Houde, a senior city planner, told the Housing Advisory Board on Sept. 28, 2022. 

In some cases, the city may be able to determine whether the neighborhood is saturated without residents having to apply for an administrative review. The city has published a map of approved ADUs. 

Typically, it takes about two months from the time someone applies to build an ADU to when they have a building permit in hand, assuming the process goes smoothly, according to city officials. 

“Much of the timeline depends on the applicant’s ability to produce good plans and address any areas of non-compliance,” Karl Guiler, a senior policy advisor for the city’s planning department, wrote in an email to Boulder Reporting Lab. 

To help expedite the perming process, members of the Housing Advisory Board want city staff to create pre-approved architectural plans for ADUs. This would allow residents to select from an array of designs that already meet many of the city’s permitting requirements. Such an incentive already exists in the City of Leavenworth, Washington.

The board members also want to increase the allowable size of the ADUs and simplify the process for calculating square footage.

Update: On Nov. 1 at 9:45 a.m., we updated the link to the Housing Advisory Board’s most recent recommendations. Here is the former link.

John Herrick is senior reporter for Boulder Reporting Lab, covering housing, transportation, policing and local government. He previously covered the state Capitol for The Colorado Independent and environmental policy for He is interested in stories about people, power and fairness. Email:

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1 Comment

  1. Another hidden impediment to developing ADUs is that many contemporary subdivisions in Boulder have HOAs (Home Owners Associations) that impose CC&Rs (covenants, conditions, and restrictions) which are deeded and run with the land and which can impose arbitrary density and use restrictions above and beyond what the City’s code requirements are. There are a fair number of subdivisions (eg. in the Parkside and Wonderland Hills areas) which include CC&Rs that prohibit renting out any “portion” of a residence or using a residence for any “non-single family use”, which effectively precludes ADU development in those subdivisions. As a home-rule municipality the City of Boulder could choose to nullify enforcement of these CC&Rs by statute but have so far failed to do so – until then, homeowners constrained by these CC&Rs will be at risk of civil lawsuits and HOA-imposed fines if they file a Declaration of Use with the County Recorder stating their intention to rent out their ADU.

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