Evan Roberts is an assistant professor in the History of Medicine and Population Studies programs at the University of Minnesota, and he leads the Minnesota Zoning Atlas project. Roberts is a demographer and economic historian who has published broadly on topics including residential segregation, social influences on health, and social science data construction. Currently, he is also working on a study of how randomized redistribution of farmland and mortgages affects life expectancy. Originally from New Zealand, he began his career working on evaluations of housing and mental health services and has lived in the Twin Cities since 2000.
Q: What is the Minnesota Zoning Atlas? How is it built and validated?
The Minnesota Zoning Atlas is part of the National Zoning Atlas, which is an effort to standardize and analyze the rules around residential building across the country. Minnesota has a lot of cities and townships. The time to analyze a small city with half a dozen zoning districts is nearly as much as a suburban city with more than 20 zoning districts. To create the atlas, our team of researchers at the University of Minnesota read the zoning codes for more than 400 cities covering more than three-quarters of the state’s population. We have read about 30,000 pages of zoning text so far. Each city’s code is examined by one analyst, and then, the work is independently reviewed. Zoning codes are complex and laid out in a range of different ways. While computers have shown a lot of promise for reading text and tables, our national partners found the accuracy of AI for picking out the key details of zoning is too low. AI tools can get the right direction, but they often fail to identify the correct numbers. Minimum lot sizes and floor area ratios matter a lot for the viability of building new homes.
Q: When you look across the state, what patterns show up immediately in the data?
Most residential land in Minnesota is zoned to only allow single-family homes—a zoning practice distinctive to the United States. In the Twin Cities metro area, there is a bit of a mismatch between cities with strong employment density and the cities allowing new housing. This mismatch means longer commutes and demand for transportation infrastructure. Minimum lot sizes in Minnesota’s cities are much larger than required for health purposes in areas served by urban sewer and water.
Zoning in Minnesota is distinct from East and West Coast patterns. In the Twin Cities, there are similarities to other large Midwest metropolitan areas that are also divided into many different cities. On the East Coast, large minimum lot sizes of a half-acre or more can often be found closer to urban centers, but this is balanced by zoning for a denser urban core with mid-rise multifamily buildings. On the West Coast, there are more areas zoned for small-lot single-family homes of less than 10,000 square feet. In the Twin Cities area, we see many suburban cities with minimum lot sizes of one-quarter to one-third of an acre. The reliance on opaque Planned Unit Developments in many suburbs to permit housing is very clear on our maps.
Q: What zoning types dominate most Minnesota cities today, and what does that mean for housing supply? Are there major differences between the Twin Cities metro and greater Minnesota?
Most residential land, about 75%, in the Twin Cities metro outside of Minneapolis and St. Paul is still zoned for single-family homes on lots of 10,000 to 15,000 square feet. Suburban cities such as Richfield and Bloomington that have moved away from exclusively single-family zones tend to only allow duplexes and retain existing lot sizes. The evidence from major U.S. cities such as Portland, Oregon, and Houston, Texas, as well as international cities like Auckland, New Zealand, show that duplex or triplex development on lots of 10,000 to 15,000 feet is not often viable. Per-unit minimum lot sizes of 1,200 to 2,000 square feet make infill townhouses and two- to eightplex (“moreplex”) development viable.
There is significant variation between Minnesota cities in their zoning for mixed-use development. Some cities have zoned for most commercial areas to allow housing either above retail and commercial buildings or stand-alone apartments. Other cities, particularlyin second- and third-ring suburbs, are more likely to strictly regulate where housing is allowed by prohibiting mixed-use buildings in commercial areas.
Zoning in small cities outside the Twin Cities metro area and in townships is distinctive. Many smaller cities outside the metro allow duplexes, “moreplexes,” or townhouses to be built in most of the city. Lot sizes and per-unit land requirements in smaller cities and towns are often significantly smaller than in metro-area suburbs, with per-unit land requirements of 3,000 to 7,000 square feet.
In small townships in greater Minnesota, we have observed an interesting pattern of most townships in a county following the same zoning regulations. However, the rules are formally adopted by the township, not the county.
Q: Are there cities that stand out as “best in class” for housing flexibility and affordability? What are they doing differently?
Minnesota cities are slowly reforming their zoning. It is notable that minimum lot sizes, and bans on duplexes, townhouses, and moreplexes, are significantly more common in many Twin Cities suburbs than in greater Minnesota cities. There are several important dimensions to improving the feasibility of homebuilding in Minnesota, and no city has adopted all of them.
Saint Paul has adopted the most missing middle-friendly zoning of any city, with 1,500-foot minimum lot sizes on most residential land. These reforms are a couple years old, and projects are being proposed that couldn’t be built in other cities.
Meanwhile, Minneapolis has streamlined rules for larger-scale multifamily buildings. Despite the attention to triplexes in the debates over the Minneapolis 2040 comprehensive plan, floor area ratio rules make building missing middle housing more difficult in Minneapolis.
Rochester has adopted useful changes to zoning administration. Small deviations from dimensional standards can be approved administratively by having staff assess the context and impact of proposed homes.
White Bear Lake has just revised its zoning code with simplified mixed-use zoning and a well-written and illustrated presentation of the code that is straightforward for residents and builders to interpret.
Q: From a builder or developer perspective, what zoning constraints most often prevent projects from moving forward before they begin?
Zoning regulations shape the value and use of land. When most residential land is zoned for single-family homes on relatively large lots, land values will be pushed down but home prices will be higher. To build or buy the home, you must have the land that goes with it. Land zoned for townhouses, moreplexes, or apartments will be expensive because regulations limit availability. For missing middle and apartment development, site acquisition in an area with the right zoning is a challenge. The dimensional rules for apartments vary across cities, increasing upfront design and development costs.
For single-family homes, many developers are trying to meet market demand by building homes on smaller lots than the zoning allows. Cities will maintain the density they zoned for by asking developers to put excess land in the subdivision into shared open spaces that must be managed by a homeowners association.
Q: How directly does zoning correlate with housing affordability in Minnesota communities?
Allowing smaller lots, missing middle housing types, and more apartments is associated with improved affordability. Measuring this is hard because new homes cost more than old homes, and new homes are often built in desirable areas. The most studied Minneapolis 2040 reforms seem to have led to lower home prices and rents than would have happened otherwise. The international evidence about zoning reform clearly shows that greater housing supply through the allowance of missing middle homes in more places and zoning for larger apartments near public transit leads to lower prices for new homes and lower rents. Missing middle zoning can also be a win-win for owners of existing homes. Because new owners can do more on the same land, missing middle reforms increase the value of existing single-family homes.
Q: Where does “missing middle” housing (duplexes, fourplexes, townhomes, ADUs) fit into the Atlas?
The Atlas distinguishes between areas that allow one, two, three, or four or more units on a lot. Four-unit lots are a very common breakpoint in zoning regulations. If you can build four units, you can often build many more, even hundreds. The rules that make building more than four units difficult are often height and bulk rules, rather than direct regulations on the number of units. In the Atlas, we record all the important dimensional rules that affect the viable building envelope: lot coverage, height, parking requirements, and floor area ratio. If a city directly limits the number of units, we display that information on the map. ADUs are mapped separately. In the Twin Cities metro, we see a lot of cities allowing ADUs in theory, but often with occupancy or public hearing regulations that make them difficult to build.
Photo Credit: Evan Roberts & National Zoning Atlas