On May 5, 2026, the City of Sun Prairie officially adopted its first ADU ordinance. The City Council approved the amendment to Chapter 17.16.140 following a Plan Commission public hearing and recommendation — and the result is one of the most permissive ADU frameworks in Dane County outside of Madison.
For Sun Prairie homeowners who've been watching neighboring cities build ADUs while their own zoning didn't allow it, the wait is over. Here's what the ordinance actually says and what it means for your property.
What the Ordinance Allows
Sun Prairie's new ordinance permits ADUs in multiple zoning districts: SR-4, MR-8, UR-12, NC, UC, CC, and PD. The core parameters:
- Maximum size: 1,000 sq ft (attached or detached)
- Height limit: 21 feet to the roof eave for detached structures, and no taller than the principal structure
- ADU types: Both attached and detached are permitted
- Units per lot: Up to one attached ADU or two detached ADUs — maximum three total dwellings per lot
- No additional parking required
- No owner-occupancy requirement
- No conditional use permit needed
ADUs are also exempt from maximum density calculations and floor area ratio limits, which means adding an ADU doesn't count against your lot's development capacity under those rules.
Why This Ordinance Stands Out
Most new ADU ordinances in Dane County come with conditions that limit who can realistically build. Owner-occupancy requirements, conditional use permits, restrictive height formulas, or narrow lot eligibility rules all reduce the number of homeowners who can actually move forward.
Sun Prairie's ordinance has none of these common barriers. No owner-occupancy means you can rent both the primary house and the ADU — or sell the property without an encumbrance following you. No CUP means no discretionary review process. The 1,000 sq ft limit matches Madison's. And the option for two detached ADUs on a single lot is more generous than most municipalities in the county.
For investors and homeowners thinking about long-term rental income, this is a clean framework to build under.
What You Need to Know Before You Start
A few practical details that matter at the planning stage:
Setbacks follow your underlying zoning district. The ordinance doesn't establish ADU-specific setbacks — your property's existing side, rear, and front setback requirements apply. This means setback constraints vary by lot. We check this during the feasibility assessment.
Entryway access is required. The ordinance specifies that ADU entryways must connect to a street frontage via a paved walkway or driveway. This is a site-planning consideration, not a barrier, but it does affect where on the lot a detached ADU can be oriented.
The principal building can't contain more than two dwelling units. If your primary structure is already a duplex, you can still build ADUs — but the ordinance caps total dwellings at three per lot.
What to Do If You're in Sun Prairie
The ordinance is live and we're ready to build under it. If you've been waiting for Sun Prairie to allow ADUs, start with a free feasibility check — we'll confirm your lot qualifies, review your zoning district setbacks, and walk through exactly what's buildable on your property.
