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

Madison has not adopted ADU-specific impact fees. Wisconsin Statute 66.0617 (Impact Fees) allows municipalities to charge impact fees for transportation, water, sewer, stormwater, parks, and public safety, but requires a fee study demonstrating new infrastructure capacity need attributable to the development. Madison's impact fees, where adopted, focus on new subdivision development on the city periphery (parks impact fee under MGO 16.23 applies to new lots) and do not target infill ADUs. Standard ADU fees include: zoning verification fee; building permit fees scaled to construction value (typically 1 to 1.5 percent of value); separate electrical, plumbing, and HVAC trade permit fees. Madison Water Utility charges water and sewer connection fees only if a new service line is installed; an ADU sharing utilities with the primary dwelling avoids these charges. Madison Metropolitan Sewerage District (MMSD) charges are typically rolled into water billing. Madison's progressive housing policy includes periodic Common Council discussion of ADU fee waivers as part of the Comprehensive Plan housing strategy and the Affordable Housing Fund.