So-called “granny flats” and “mother-in-law suites” are now permitted at residential properties Denver-wide after the Denver City Council voted unanimously on Monday night to amend the city code on accessory dwelling units.

A trio of bills approved by the council permits accessory dwelling units or ADUs in all zone districts that allow residential use, updates the municipal code and amends the city zoning map to incorporate these changes.

“In every corner of our city, the cost of housing is top of mind for Denverites, and simple improvements to our policies like this make a real difference for working families. As we continue to push to create thousands of units of affordable housing, giving residents the option to build an ADU will not only make it easier for families to stay in Denver long-term, but will put us one step closer to tackling the challenge of housing affordability.” 

Accessory dwelling units are self-contained, smaller living spaces with their own kitchen, bath, and sleeping area that are an extension of an existing property, either attached or detached. They are often called mother-in-law suites, granny flats, casitas, backyard cottages, garage apartments or basement apartments. 

“By adding accessory dwelling units to all the residential zone districts within the Denver zoning code, we are actually able to delete 16 districts that aren’t needed,” senior city planner Justin Montgomery said.

By eliminating the need for case-by-case analysis for ADUs, officials said it would lead to significant savings in city resources, as well as resident’s time and money.

“A few years ago, I looked at the numbers and about 60% of re-zonings that were coming through were individual re-zonings,” Vice Chairman of the Planning Board Fred Glick said. “Even though we found ways to expedite them, it’s an incredible amount of time and resources on the part of city staff and the applicants.”

ADUs have been part of the city’s ongoing effort to expand housing availability and options, according to the city’s website, but have been hampered by what city officials call a “one-size-fits-all” approach that didn’t reflect the individual character of each neighborhood.

“I think living in a city with a housing crisis and looking at just the scope of what we need to do to really meet that crisis, often we look at the macro, like we’ve got to get those 44,000 units, get them built so that we can make Denver more affordable,” District 9 Councilmember Darrell Watson said. “It’s often easy to overlook the small steps we can take to empower our neighbors to be a part of gentle density in our communities.Accessory dwelling units will not solve our housing crisis, but it’s an important first step.” 

The measure, which has been in the works for two years, will bring the city closer to the new state law, which requires local governments to allow the construction of ADUs on residential properties, which takes effect in 2025.

The city and the state differ on one small element: setbacks.

Colorado’s House Bill 1152, which went into effect in 2024, limits ADU setbacks to 5 feet from the side and rear of a property.

City officials said there may be cases when a bigger setback may be appropriate in some neighborhoods.

The City Council plans to address the matter with the state before the new law is implemented after the next legislative session, officials said. 

“We’re going to go back to the state legislature and we’re going to once again, refer to them all the work that we did, and how Denver is a more complex land use environment than probably any other city in Colorado,” District 10 Councilmember Chris Hines said. “So, we are hopeful that we will continue to prevail with amendments at the state level.”

Denver Gazette reporter Alexander Edwards contributed to this report.