The Rules Today
| Rule | Madison, as of October 2026 |
|---|---|
| Where | A permitted use in all 15 residential districts, plus the A, NMX, TSS, CC-T, DR1 and DR2 districts, on lots whose main building has up to 8 units.(MGO 28.032) |
| Kinds | One attached ADU (an addition, or inside the house, basement and attic included), or one detached building with one or two units. Not both.(MGO 28.151) |
| Size | Attached or interior: up to 1,000 sq ft. Detached: a footprint up to 1,000 sq ft, 25 ft tall; the units can fill the whole building. District lot coverage limits still apply. |
| Setbacks (detached) | At least 3 ft from rear and side lot lines (side only if it's behind the house), and 3 ft from the house and other buildings.(MGO 28.131) |
| Owner occupancy | Not required since April 2024. The ADU can't be sold separately. |
| Parking | None required.(MGO 28.141) |
| Design | A side or rear entrance needs a paved walk or drive to the street. An attached ADU can't make the house stop looking like a house. No matching-materials rule. |
| Occupancy | Each unit can house one family, which in Madison includes up to five unrelated adults. |
| Address | Its own, assigned by City Engineering.(City of Madison) |
How the Rules Changed
If a page tells you Madison requires owner occupancy, caps ADUs at 900 sq ft or limits them to two bedrooms, it's describing rules that no longer apply.
| When | What changed |
|---|---|
| Before Dec 2021 | Conditional use with a Plan Commission hearing. Owner occupancy, single-family homes only, 900 sq ft and two bedrooms max. Source |
| Dec 2021 | ADUs become a permitted use: no hearing (ORD-21-00087). Source |
| Jan 2023 | ADUs allowed with two-family homes inside the Transit-Oriented Development overlay (ORD-23-00013). Source |
| Mar 2023 | Occupancy changed to 'one family', which allows up to five unrelated adults (ORD-23-00022). Source |
| Apr 2024 | Owner occupancy removed; ADUs allowed with buildings of up to 8 units (ORD-24-00022). Source |
| Mar 2025 | Size raised to 1,000 sq ft; bedroom cap removed (ORD-25-00011). Source |
| Sep 2025 | Wording cleanup (ORD-25-00057). Source |
| Oct 2025 | Two units allowed in one detached building; the ADU no longer counts against the lot's 1,000 sq ft accessory-building cap (ORD-25-00068). Source |
Steps and Timeline
- Check the zoning of your lot, and whether it's in a historic district, the floodplain or a PD zone, which add review.
- Preliminary review with Zoning (608-266-4551 ext. 3): bring a scaled site plan, elevations and a floor plan.
- Site plan review: email the plans to the City. Agencies review them, Parks bills the impact fee and Engineering assigns the address. About 2 to 3 weeks, $100.(City of Madison)
- Building, plumbing, electrical and HVAC permits, pulled by licensed contractors. Initial plan review takes 10 to 15 business days.
- Inspections, then a Certificate of Occupancy.
Fees
- Site plan review: $100 for a lot up to an acre.
- Park impact fee: $5,026.88 for 2026 ($1,437.62 infrastructure plus $3,589.26 land), due when the building permit is issued, by check. The City's attached-ADU page still says "about $4,500", which is the older figure.(Madison Parks)
- Building permit: $0.10 per sq ft for new construction or additions, or $11 per $1,000 of value for alterations such as a basement conversion; plan review $100 for a new building or $25 for an alteration; a $50 certificate of occupancy. Trade permits are extra.(MGO 29.09)
Utilities
- Electric: the ADU needs its own meter and panel.
- Water: a contractor confirms with Madison Water Utility that the existing lateral can serve both units; if not, it's upsized or a new one is run. A separate meter means a new service from the street.
- Sewer: if the house and ADU share one sewer lateral, a deed restriction has to be recorded.(City of Madison)
Basement and Attic ADUs
Zoning calls an interior unit an ADU, but under the building code Madison enforces, a house with two units is a two-family dwelling. That brings fire-rated drywall between the units, 20-minute rated doors, separate exits for each unit and alarms in each. Adding a unit to a building that already has two or more makes it a three-unit building under the commercial code, which city staff say means an accessible unit and sprinklers.(City staff memo) See what the code asks of each kind of ADU and egress window rules on badgerremodel.com.
Renting It Out
Long-term rental is allowed. Short-term rental is tighter: if you live in the main house, you can't rent the ADU for stays under 7 nights. If you live in the ADU, you can rent the ADU but not the house. Stays of 7 to 29 nights are allowed without it being your residence, up to 180 days a year. Each needs a tourist rooming house permit ($300, then $100 a year), a Public Health license and room-tax registration.(City of Madison STR FAQ)
Cost and Financing
City staff wrote in 2024 that a detached ADU commonly costs $200,000 to $300,000, and that about 32 had been built since 2012.(City staff memo) The City's 2022 "Backyard Homes" loan (2% over 15 years, up to $130,000) funded four ADUs and ran out in 2023; we found no current City ADU loan.(RES-22-00354)
Questions
Do I have to live on my property to build an ADU in Madison?
No. Madison removed the owner-occupancy requirement in April 2024 (ORD-24-00022). Some older pages, including a 2023 post on the Mayor's blog, still say it's required.
How big can an ADU be in Madison?
An attached or interior ADU can be up to 1,000 sq ft. A detached ADU building can have a footprint up to 1,000 sq ft and be 25 ft tall, and the unit can fill the whole building, including a basement and upper floor. The old 900 sq ft and two-bedroom limits were removed in March 2025.
Can a backyard ADU in Madison have two units?
Yes. Since October 2025 a detached ADU building can hold two units. A lot can have that, or one attached ADU, but not both.
Do I need a public hearing?
No. An ADU has been a permitted use since December 2021. You need a $100 site plan review and building permits. A conditional use is needed only for things like exceeding the accessory-building limits, or in a historic district or PD zoning.
Does an ADU in Madison get its own address?
Yes. City Engineering assigns one during site plan review.
Can I put my Madison ADU on Airbnb?
If you live in the main house, not for stays under 7 nights. If you live in the ADU, you can rent the ADU but not the house. Stays of 7 to 29 nights don't need to be your primary residence but are capped at 180 days a year. A tourist rooming house permit costs $300 plus $100 a year.
Related Guides
- ADU rules in other towns around Madison.
- Madison remodel permits: which projects need one, fees and who to call.
- How new construction affects your Madison property tax.
Checked against Madison General Ordinances as codified through ORD-26-00040 (August 2026) and City pages in October 2026. Confirm with Zoning before you design. This is a guide, not legal advice.