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

Fitchburg's accessory dwelling unit (ADU) rules sit in Chapter 22, Zoning, Sec. 22-230, adopted by Ord. No. 2025-O-17 on September 9, 2025. The section caps every lot of record at one ADU and requires the unit's entrance to open onto the side or rear yard rather than the street-facing front. On utility hookups, the ordinance gives owners two paths. Under subsection (7), an ADU may share the primary home's existing water and sewer connections if the building inspector finds adequate capacity and signs off, and any new plumbing work still has to be permitted and inspected like any other job.

Owners who instead run new, separate lines for the ADU do not get a break: subsection (8) states plainly that new, separate utility connections are billed the typical fees and charges the city applies to any new residential dwelling unit, so the ADU pays full freight rather than a reduced accessory-unit rate. The ADU must be served by permanent water and sewer service under subsection (6); a travel trailer or RV cannot stand in for one. Subsection (9) bars selling the ADU apart from the principal dwelling, and subsection (10) layers on design limits for ADUs paired with single-family or duplex lots: floor area capped at 75 percent of the principal unit's area, a detached-building height cap of 25 feet, and exterior finish, roof pitch, trim and window proportions that must match the main house. For ADUs on multifamily lots, the height cap under subsection (11) rises to two stories or 30 feet, whichever is less.