Madison, WI Accessory Structures: ADU Impact Fees (2026)
Key Facts
- ADU fee category
- Multi-Family Park Impact Fee (with 3-family+ units)
- Land dedication rate
- 734 sq ft per unit, or fee in lieu
- Infrastructure fee
- $1,032 per unit (2016 base, indexed annually)
- When fee is due
- Before building permit issuance
- Low-cost housing exemption
- Available under Wis. Stat. § 66.0617(7)
- Benefit district split
- 20% citywide, 80% to local district
Summary
Madison doesn't have a separate ADU impact fee: accessory dwelling units are billed under the Multi-Family Park Impact Fee category set by Madison General Ordinances § 20.08(2). Developers owe a Park-Land Impact Fee (734 square feet per unit, or cash in lieu) plus a Park-Infrastructure Impact Fee of $1,032 per unit, indexed annually from a 2016 base.
2.Park Impact Fee Categories. Park Impact Fees shall be based upon the five following categories of development:a.Single-Family or Duplex... b.Multi-Family. Includes all three-family and multi-family dwelling units with three (3) or fewer bedrooms, as well as accessory dwelling units... Type of Development / Square Feet/Unit or Lodging Room / Multi-Family / 734 ... Type of Development / Fee/Unit or Lodging Room / Multi-Family / $1,032
Full Breakdown
b defines the City's "Multi-Family" Park Impact Fee category to include "all three-family and multi-family dwelling units with three (3) or fewer bedrooms, as well as accessory dwelling units", meaning ADUs are folded into this bucket rather than treated as their own fee class. 08(2)(c)4, the Park-Land Impact Fee requires dedicating 734 square feet per unit for this category (or a fee in lieu, calculated from the citywide average assessed land value per square foot, if the Plan Commission finds dedication impractical). b sets the Multi-Family rate at $1,032 per unit, set in 2016 dollars and indexed every January 1 using the Engineering News-Record Construction Cost Index.
Twenty percent of that fee funds a citywide district; the remaining 80% goes to one of five benefit districts (North, East, Central, West, or City-Wide) based on where the development sits. The fees phased in gradually, 80% in 2017, 90% in 2018, and full amount from 2019 onward. 22(7), under authority granted by Wis. 0617(7), though that exemption applies only to the qualifying units within a project, not the whole development.
Violations & Fines
Under § 20.06(1)-(3), no rezoning permit, conditional use permit, or building permit may be issued for a development, including one adding an ADU, until the Park Impact Fee is calculated and noticed for collection, and for unplatted land the fee must be noted on the face of the recorded plat or certified survey map.
Frequently Asked Questions
Do accessory dwelling units pay a separate ADU impact fee in Madison?
When is the Madison Park Impact Fee collected?
Can a low-income ADU skip the impact fee?
Does the ADU impact fee amount change every year?
Sources & Official References
Other rules in Madison
Compare Madison to another location·View the Wisconsin accessory structures overview
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ADU Impact Fees in Nearby Cities
How other cities in Dane County handle adu impact fees.