Des Moines moves to allow construction of Accessory Housing Units throughout the city

The City of Des Moines will dramatically expand homeowners' ability to construct Accessory Dwelling Units (ADUs) under an amendment to the city’s zoning code adopted by Council Monday night. ADUs are smaller homes that share a lot with a larger single-family home.

A graphic shows that ADUs can be built as detached units or be attached to a house by sharing walls, being built in an attic or basement, or even a converted garage.
ADUs can be build as stand-alone buildings or connected to the exisitng home in a variety of ways. (Image: City of Des Moines)

The changes allow ADUs to be built in residential areas across the city, a significant expansion over the earlier code, which only allowed them in areas already zoned for multifamily development. A press release by the City of Des Moines estimates ADUs will be allowed on 78 percent of the city's residential land following this change. In the remaining areas, other forms of multifamily housing are allowed.


Under this action by Council, ADUs would be legal to build “by right,” or with minimal city approvals, in more than half the city, including land already zoned for multifamily housing as well as areas near DART transit lines. With a conditional use permit approved by the Zoning Board of Adjustment, these homes would be allowed in other residential areas.


“We're trying to provide alternative housing options that give people different choices and provide more rooftops in Des Moines. I think that it's particularly important on our corridors and transit routes that have that extra layer of density but [need development that is] done in a way that is sensitive to the character of the neighborhood,” said Des Moines planning and urban design administrator Jason Van Essen.

Ahead of the vote, the City of Des Moines released a new resource explaining restrictions that apply to ADUs built in the city, including that they are restricted to half the size of the main house on the property and include on-site parking.


In addition, the property owner must live either in the main house or the ADU but can obtain a rental certificate for the other home on the lot if someone who is not in the homeowner's immediate family will live there. That move is intended to boost neighbors’ confidence that ADUs will not interfere with surrounding owner-occupied homes.


“An owner has to reside on the property, so you’re always going to have the actual property owner invested in what happens on that property, and I think more of the challenges that we’ve seen historically with properties that are rented is often you have the absentee landlord,” Van Essen said.


Van Essen said that while the city does not have a count of the current number of ADUs in Des Moines, they can be found in several neighborhoods. He estimated their number in the dozens, but not the hundreds, city-wide.


Local nonprofit HOME, Inc., is constructing one ADU in the Oak Park neighborhood of Des Moines. The Polk County Housing Trust Fund is tracking the construction of that home with videos on its YouTube channel.

Around the country, ADUs are known as a “gentle density” form of housing development which means neighbors may not even notice their addition on a given block. Des Moines city officials have said the expansion of ADU access aligns with changes to the city’s zoning code in 2019 and the city’s comprehensive plan, which calls for increasing housing options at various price points.


As an affordable housing strategy, one advantage of ADUs is that they do not require buying more land because they share a lot with another home. They are also an effective way of allowing smaller rental units into single-family neighborhoods where they may not otherwise be allowed, according to The ABCs of ADUs, a publication by the AARP, a national leader in advocating for ADUs across the country.


AARP also points out that ADUs are an excellent way for multiple generations of a family to live on the same property while each can keep their independence.


“It’s one thing that can be done to try to provide a variety of options for folks that are at different points in their lives,” Van Essen said. “We want to maintain our sense of place but also try to provide more housing, so I think this is a great way to do that.”


This change in zoning is the second recent policy change Des Moines has made to support more housing choices. In November, the city adjusted its development incentives to provide tax abatements for ADUs and missing middle housing – smaller multi-family developments that occupy the middle ground between single-family homes and larger apartment buildings.


Around the country, multiple changes in city codes are often necessary to spur more construction of ADUs. Van Essen acknowledged Des Moines' current actions might not be its last.


“You know zoning – it's all a living document [that’s] constantly being evaluated and changed, and so we’ll... continue to look at this and see how it goes and make changes in reaction to what we see,” he said.


Editor’s note: In the Des Moines zoning code, ADUs are referred to as Accessory Housing Units or AHUs. The two terms can be used interchangeably to describe the same type of housing.


This blog post was updated on May 10 to incorporate information from a City of Des Moines press release.