Accessory Dwelling Units approved by Plan Commission
by Andy Schoenherr
Editor, Sun Prairie Rising
Sun Prairie officials are starting work on policy changes that will have a significant impact on how the city grows for decades: a complete rewrite of the city’s zoning code.
On March 4th, the Planning Commission got its first look at an early draft of the new rules. For now, the discussion is just the beginning of what will likely be a long public process. One aspect of the plan, related to ADUs or accessory dwelling units, is moving forward, but no major decisions on the overall code have been made yet.
The changes being considered could eventually affect everything from what kinds of homes get built to how neighborhoods look and where businesses can locate.
Why the City Is Rewriting the Rules
Sun Prairie’s current zoning code is old. The last major update was in 1989, and city planners say the rules have become complicated, outdated, and sometimes hard for residents, developers, and even city staff to navigate.
In the 35+ years since, the city has changed dramatically.
Sun Prairie has more than doubled in population over the past three decades and now has almost 40,000 residents. Housing demand across Dane County has also surged, pushing rents and home prices higher, putting pressure on communities to allow more housing.
City officials say the goal of the rewrite is not just to tidy up old regulations. They want the new rules to better match the city’s long-term vision for growth, housing, transportation, and sustainability.
In other words, zoning isn’t just about buildings. It shapes how a community lives.
A Different Way of Thinking About Zoning
One of the biggest shifts in the draft of the new plan is a move toward what planners call a “form-based” zoning code.
Across the country, many cities are reconsidering zoning rules that strictly segregate different housing types into different neighborhoods, and separate housing from businesses. Research suggests newer “form-based” approaches can lead to more walkable neighborhoods, a wider range of housing types, and more community involvement.
A form-based code looks more at how buildings fit into a neighborhood — things like height, placement on a lot, and how buildings interact with the street.
The goal is to create neighborhoods that are more sustainable and predictable in how they develop.
The draft would organize zoning districts along a spectrum — from rural or natural areas all the way up to more urbanized corridors and downtown areas — based on how intense development is expected to be.
As a growing suburb near a growing metro area, Sun Prairie also bumps up against Townships and rural farmland, so it needs the flexibility to adjust land-use designations for a variety of different property types and locations.
Why Housing Is a Big Part of the Conversation
Housing is the single biggest reason driving the proposed updates to the zoning code. Providing residents with safe, stable housing choices that fits a diverse mix of price points and income levels is critical to a thriving community.
Increasingly, counties and municipalities are searching for solutions at the local level. The US Senate recently voted 89-10 to pass a bipartisan bill to increase the supply of new houses and restrict purchases by private investors. But it faces hurdles from the Republican-controlled House and the Trump administration has not highlighted the bill as a priority.
Local officials have heard time and again that limited housing supply and rising costs are a major concern for both residents and employers in the region.
Dane County makes up about 10% of the state’s population. But between 2010 and 2021, the strong economy here accounted for 27% of Wisconsin’s total job growth, bringing more workers and families looking for places to live.
As a result, median home prices in Dane County climbed from about $226,000 in 2010 to $369,000 in 2022, pushing even higher in the years since.
Rents have also climbed rapidly in recent years. Madison Housing data shows that median rents for one- and two-bedroom apartments have increased about 47% since 2020, while the typical monthly rent in Dane County is now close to $2,000 per month, all with a below average vacancy rate.
Roughly one in four households now spend more than 30% of their income on housing, leaving less available for the rest of the local economy.
The city’s comprehensive plan calls for neighborhoods with a wider mix of housing types, rather than areas dominated by just one style of home.
That could include units in the “missing middle” – townhomes, condos, duplexes and four-plexes that fit into traditional neighborhoods while adding more affordable housing choices.
City planners say zoning rules often determine whether those options are even possible to build.
Changes That Could Affect Neighborhood Design
The new code may also include changes aimed at improving neighborhood design.
For example, one idea being studied involves limiting large front-facing garages so that homes emphasize front doors, porches, and pedestrian-friendly streets instead of rows of garage doors.
City staff say the goal is to avoid what planners sometimes call “garage-scapes” — neighborhoods where garages dominate the streetscape. Most newer neighborhoods in Sun Prairie, such as Providence, Liberty Square, and Smith’s Crossing, include similar provisions- the challenge is identifying a solution that allows flexibility and options for emphasizing the home while providing a range of design solutions for builders.
ADUs Moving Forward
One change that’s being adopted relatively quickly relates to “accessory dwelling units” or ADUs, sometimes called backyard cottages or in-law apartments.
These small secondary homes are increasingly being considered by many cities as a way to add housing without dramatically changing neighborhood character. Nearly all communities in Dane County allow ADUs, with Madison, Middleton, and Waunakee recently updating their standards.
The Staff Report presented at the March 10th meeting explains that regulations in the early 20th century effectively outlawed these types of homes in suburban areas, but notes, “ADUs have been making a comeback, from a regulatory perspective, over the past 15-20 years as housing prices have steadily risen faster than household incomes, and some of those early zoned neighborhoods have matured and people begin reinvesting in their properties.”
The Commission recommended approval of an ordinance to permit ADUs, after several amendments proposed by Commissioner Mark Brehmer.
Per the ordinance, homeowners would have to apply for a Special Use Permit (SPU) and meet certain requirements before adding on to their existing home. Covenants might also prevent ADUs from being constructed on some lots.
The first reading of the ordinance will be delayed until the City Council meeting on April 21 so that the vote can be taken after the new (post-election) City Council is seated. The standard practice in Sun Prairie is to have an ordinance read at two Council meetings before any action is taken.
Given the ongoing housing challenges in the area, city officials see the value in ADUs to provide another option to alleviate costs and accommodate situations with inter-generational and non-traditional housing arrangements.
Possible Incentives for Developers
The draft plan also includes the idea of “incentive zoning.”
Under this approach, developers could receive certain allowances — such as permission to build slightly taller buildings or add more units — if they provide community benefits like affordable housing or improved stormwater management – at no cost to the city. Madison has approved three projects since adopting their incentive zoning program in 2023, and Middleton adopted a similar program in 2024.
The goal is to encourage development that helps the city meet broader policy goals. This aspect of the plan is likely to be met with skepticism from many area residents who oppose any kinds of incentives for developers. The specific benefits to the city and community will need to be debated and clarified before any final changes are approved.
A Long Process Ahead
The project started in 2024 with nearly two years of studying the city’s existing development patterns, development approvals, and surveying residents. Still, city officials emphasized that the draft presented to the Plan Commission is only the beginning.
The version currently under review includes about two-thirds of the eventual ordinance, with the remaining sections expected later this spring.
Over the next several months, the proposal will be reviewed by multiple city committees and discussed at public meetings. Community engagement events and public feedback sessions are also planned.
If everything stays on schedule, the city could have a full draft ready for broader public review later this year, followed by hearings and potential adoption.
At the March 4th meeting City Planning Director Josh Clements stressed that communication will be key in the process. “We want to remind people that we’re aiming towards better outcomes,” Clements said.” “Most of our residents don’t encounter zoning in their lifetimes at all, if so only occasionally. So we need to help people understand what this means for them…with tangible examples.”
In the meantime, officials say the goal is simple: create zoning rules that are easier to understand and better suited to the way Sun Prairie is growing.
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