Madison, WI Accessory Structures: ADU Impact Fees (2026)

Chapter 20 of the Madison General Ordinances, the Impact Fee Ordinance, imposes park impact fees city-wide under Sec. 20.08(2). The category rule sits in Sec. 20.08(2)(c)2.b: the Multi-Family category covers three-family and multi-family units with three or fewer bedrooms "as well as accessory dwelling units," so an ADU is charged as a Multi-Family unit. Single-Family or Duplex, which covers detached, attached and two-family dwellings, pays more on both fees: $1,520 per unit instead of $1,032 for the Park-Infrastructure fee, and 1,081 square feet of land instead of 734 for the Park-Land fee.

The Park-Infrastructure Impact Fee is stated in Year 2016 dollars and is indexed on January 1 of every year, with 2016 as the base year and the Engineering News Record Construction Cost Index as the measure. The amount actually owed is therefore the annually adjusted rate in effect when the permit issues, not the printed $1,032. The three-year phase-in (80 percent in 2017, 90 percent in 2018, 100 percent from 2019) is complete, so the full rate applies. Twenty percent of each Park-Infrastructure payment goes to the City-Wide District and eighty percent to the benefit district where the lot sits: North, East, Central or West.

The Park-Land Impact Fee is the 734 square feet per unit, less any land dedications or credits, multiplied by the city-wide average assessed value of land per square foot as of January 1. It is paid in lieu of dedication when the Plan Commission, after a recommendation from the Park Superintendent or Board of Park Commissioners, finds dedicated sites would be too small to use, the Comprehensive Plan places parks elsewhere, or the site is unsuitable.

Timing is set by Sec. 20.09(1): fees are due in full at building permit issuance, with an option to pay earlier at plat or certified survey map recording. Sec. 20.06(3) bars any rezoning, conditional use or building permit until the fees are calculated. Sec. 20.16(5) lets the City and a developer agree to a credit against the Park-Infrastructure fee for improvements to public parkland under an approved park master plan.

Low-cost housing is exempt from the park impact fees under Sec. 20.08(2)(d), but only for the units determined by the Community Development Division to be affordable under Sec. 4.22(2) and deed restricted under Sec. 4.22(7). The exemption does not reach the land dedication rules in Sec. 16.23(6)(f) or other impact fees.