An accessory dwelling unit (ADU) is a second, complete home on a lot: a backyard cottage, an apartment over the garage, an addition, or a unit in the basement. Madison now allows one on almost any residential lot with no hearing. The towns around it range from a permitted use to not allowed at all. Here is each town's current rule, from its own code.
Rule finder · Towns compared · What the building code asks · Steps · Money · Renting it out
Every town compared
| Town | How it's approved | Size limit | Owner must live there | Parking |
|---|---|---|---|---|
| Madison | Permitted use, no hearing | 1,000 sq ft (detached: 1,000 sq ft footprint, 25 ft tall) | No (since April 2024) | None |
| Middleton | Zoning permit, decided within 30 days | No larger than the house | Yes, 10 months a year (recorded agreement) | None |
| Fitchburg | Not stated in the code; ask Planning | 75% of the house (detached: 25 ft tall) | No | Not stated |
| Monona | Conditional use, public hearing | Accessory limits: 14 ft tall, 1,000 sq ft of accessory buildings | Required as an approval condition so far | None found |
| Shorewood Hills | Not allowed (under discussion) | — | — | — |
| Sun Prairie | Special use: staff review, no hearing, $250 | 1,000 sq ft (detached: 21 ft to the eave) | No | None |
| Verona | Permitted use (RA and NR districts) | 900 sq ft or half the house, whichever is less | Yes, in the main house | Yes, extra spaces |
| McFarland | Conditional use, limited occupants | Min. 800 sq ft per unit | Occupant limits instead | Per bedroom count |
| Maple Bluff | Not allowed (family suites only) | — | — | — |
| Unincorporated Dane County | Conditional use in most districts (about 3 months) | 800 sq ft, 2 bedrooms | Yes, in either unit | 1 space |
From each town's zoning code and planning records, October 2026. Wisconsin has no state ADU law, so these local rules are the whole story. (AB 449)
Town by town
City of Madison
- Approval: Permitted use. A $100 site plan review (about 2 to 3 weeks), then building permits. No public hearing.
- Size: Attached or interior: up to 1,000 sq ft. Detached: a building footprint up to 1,000 sq ft and 25 ft tall, holding one or two units.
- How many: One attached ADU, or one detached building with up to two units. Not both.
- Owner must live there: No. The owner-occupancy rule was removed in April 2024. The ADU can't be sold separately.
- Parking: None required.
- Fees: $100 site plan review, a park impact fee of $5,026.88 (2026), and building permit fees.
- Short-term rental: Only if the operator lives in the ADU itself, except stays of 7 to 29 nights.
Read the ordinance · Call City of Madison Zoning, 608-266-4551 · Madison in depth
City of Middleton
- Approval: Permitted use. A zoning permit from the Zoning Administrator, decided in writing within 30 days, plus building permits.
- Size: No larger than the main house's floor area. The ADU must meet the main-house setbacks, not the lighter accessory-building ones.
- Owner must live there: Yes, on single- and two-family lots: in the house or the ADU at least 10 months a year, under an agreement recorded with the City before the permit.
- Parking: None required.
- Fees: Zoning permit $50 to $300. Park fees are waived for ADUs by code.
- Address: The ADU gets a suite number, not its own street number.
- Short-term rental: Allowed with City, state and Public Health licenses. Stays of 1 to 6 nights must be in the operator's primary residence.
Read the ordinance · Call Middleton Planning & Community Development, 608-821-8370
City of Fitchburg
- Approval: The 2025 ordinance doesn't say whether ADUs are by right or need Plan Commission review; ask Planning. Reducing side or rear setbacks takes a conditional use permit.
- Size: Up to 75% of the house's floor area. A detached unit can be 25 ft tall.
- How many: One per lot.
- Owner must live there: No. The ADU can't be sold separately.
- Design: Siding, roof pitch, trim, eaves and windows must match the house. Entrance on the side or rear.
- Fees: 2026: zoning fee $50 plus $0.09 per sq ft; water impact fee $958 if it gets its own connection.
- SmartCode areas: In T-zone neighborhoods an 'Accessory Unit' up to 600 sq ft is allowed by right.
Read the ordinance · Call Fitchburg Planning & Zoning, 608-270-4200
City of Monona
- Approval: Conditional use with a Plan Commission public hearing, usually over two meetings.
- Size: No ADU size rule. As an accessory building: 14 ft tall, and all accessory buildings together up to 1,000 sq ft. Earlier approvals capped units at 75% of the house or 700 sq ft.
- Owner must live there: Every approval so far has required it, and the ADU can't be sold separately.
- Address: Approvals have required the ADU to share the house's address.
- Track record: City staff counted one permitted ADU in Monona as of October 2024.
Read the ordinance · Call Monona Planning Department, 608-222-2525
Village of Shorewood Hills
- Today: Not allowed in any district.
- What's next: The Plan Commission has discussed ADUs since 2024 and lists them for possible action on October 13, 2026. Members have leaned toward requiring owner occupancy if ADUs are allowed.
Read the ordinance · Call Village of Shorewood Hills, 608-267-2680
City of Sun Prairie
- Approval: Special use permit: staff review within 10 working days of a complete application, no public hearing, $250. Then a building permit.
- Size: Up to 1,000 sq ft. A detached building can be 21 ft to the eave and no taller than the house.
- How many: One attached ADU, or up to two detached ADUs. Never more than three homes on the lot.
- Owner must live there: No requirement in the code.
- Parking: None required.
- Short-term rental: The City has no short-term rental ordinance; state and county licensing apply.
- New rule: Adopted May 5, 2026 (Ord. 984), so expect staff interpretations to develop.
Read the ordinance · Call Sun Prairie Planning Division, 608-825-1107
City of Verona
- Approval: Permitted use in RA and NR, plus a building permit.
- Size: The lesser of 900 sq ft or 50% of the house. A basement unit can fill the whole basement.
- Owner must live there: Yes, in the main house (not in the ADU).
- Parking: Extra off-street spaces beyond the house's two, not in the front yard and not stacked behind the house's spaces.
- Design: Behind the house, sharing its driveway, matching its roof pitch, materials, windows, trim and color.
- Short-term rental: Only in the owner's primary residence, stays of 7 to 180 days, with a City license.
Read the ordinance · Call Verona Planning & Development, 608-845-6495
Village of McFarland
- What's allowed: No ADUs by name. A 'temporary auxiliary apartment' inside a single-family house, for an elderly or disabled person or a relative or attendant.
- Approval: Conditional use: Plan Commission public hearing, survey and notice to neighbors within 400 ft. $500 plus legal and engineering costs.
- Size: At least 800 sq ft per dwelling unit, not counting halls, entries and basements.
- Another route: Converting a single-family house to a two-family is also a conditional use in R-1 through RH-1.
Read the ordinance · Call McFarland Community & Economic Development, 608-838-3154
Village of Maple Bluff
- Today: ADUs aren't a listed use in the June 2025 zoning code, and unlisted uses are prohibited. No detached accessory building may be a dwelling.
- What's allowed instead: A family suite inside the house, 'generally intended for an extended family member or adult child': its own kitchen, bath and living areas, connected to the house by a permanent unlocked interior passage. Outside access only by porch, patio or deck, no separate address, utilities or meters, and the house has to look like one house.
- Short-term rental: No rentals of 6 nights or fewer; 7 to 29 night rentals need a village license, up to 180 days a year.
Read the ordinance · Call Village of Maple Bluff, 608-244-3048
Towns under Dane County zoning
- Where: Only in towns that use Dane County zoning, not inside cities or villages.
- Approval: In most districts a conditional use permit: the town board recommends, and the county Zoning and Land Regulation Committee decides. About three months. Application $495 (2021 schedule).
- Size: Up to 800 sq ft and two bedrooms.
- Owner must live there: Yes, in the house or the ADU. The ADU can't be sold separately.
- Parking: One off-street space for the ADU, in addition to the house's.
Read the ordinance · Call Dane County Zoning Division, 608-266-4266
What the building code asks of each kind of ADU
Zoning decides whether you can have an ADU. The state Uniform Dwelling Code decides how it's built, and it treats every ADU as a home, not an outbuilding. (SPS 320.07)
Backyard cottage
A new one-family dwelling in its own right: footings below the frost line or 48 inches deep, the full energy code if it's heated, and its own exits and alarms. (SPS 321.16) Distance from the house matters: under 5 feet apart, both facing walls need fire-rated construction; 5 to 10 feet, one of them; over 10 feet, neither. (SPS 321.08)
Over or inside a garage
Turning a garage into a home is a change of use, so the whole dwelling code applies, not just the remodeling rules. (SPS 320.04(4)) That usually means checking whether the slab and footings meet the frost-depth rule, insulating to the energy code, and, for a unit over a garage, 5/8-inch Type X drywall on the garage side and a 20-minute fire-rated door between garage and home.
Basement or attic unit, or an attached addition
A second unit in the house makes it a two-family dwelling under the code. The two units need:
- 5/8-inch Type X drywall on each side of the walls between them, and on the ceiling under an upper unit. (SPS 321.08(2))
- Labeled 20-minute fire-rated doors between the units, including a door from the main house down to a basement unit.
- Fire dampers or firestopping where ducts and pipes pass between units.
- Exits of their own for each unit. A basement unit with bedrooms usually needs an egress window in each bedroom. (SPS 321.03(10))
- Smoke alarms and, with a fuel-burning appliance, CO alarms on each floor of each unit.
The code doesn't require sound insulation between units or a separate furnace, but a landlord has to tell a tenant if the heat can't hold 67°F. (DATCP) For the basement itself, see what to check before you finish a basement.
How an ADU project goes
- Check your zoning. Your town's map tells you the district; the finder above tells you what that district allows.
- Talk to the zoning office early. Bring a rough site plan, so a setback or size problem shows up before anything is drawn in detail.
- Plan utilities. Madison requires a separate electric meter for the ADU, and a shared sewer lateral needs a deed restriction. Water service may need upsizing.
- Get the zoning approval: a site plan review, zoning permit, special use or conditional use, depending on the town.
- Building permits and plan review for the building, electrical, plumbing and HVAC work.
- Build, inspect, occupy. Rough, insulation and final inspections, then occupancy.
Money
- Building it: Madison city staff put a detached ADU at $200,000 to $300,000 in 2024. (City staff memo) Conversions of existing space usually cost less, because the foundation and shell already exist.
- Town fees: Madison charges a $100 site plan review and a $5,026.88 park impact fee (2026); Middleton waives park fees for ADUs; Fitchburg charges a zoning fee of $50 plus $0.09 per sq ft; Sun Prairie's special use permit is $250.
- Loans: Madison's "Backyard Homes" ADU loan (2022) has ended; we found no current city ADU loan program.
- Property taxes: the parcel is reassessed at full market value, as of January 1. A half-built ADU is assessed as it stands that day. (DOR assessment manual)
Renting it out
A rented ADU falls under Wisconsin's landlord-tenant rules (Wis. Stat. ch. 704 and ATCP 134): (DATCP guide)
- Return the security deposit, less proper deductions, within 21 days after the tenancy ends.
- Give written receipts for deposits and cash rent, and at least 12 hours' notice before entering.
- If the units share a utility meter, explain in writing how the bills are split.
- Disclose known code violations and problems such as heat that can't keep the unit at 67°F.
Short-term rentals (under 30 nights) need local and state licenses, and most towns here limit them to the operator's own primary residence.
Frequently asked questions
Can I build an ADU in Madison?
Yes. Since December 2021 an ADU is a permitted use in every residential district, so there's no public hearing: a $100 site plan review and then building permits. Since April 2024 you don't have to live on the property. Madison's rules in depth.
Do I have to live on the property?
Depends on the town. Madison, Sun Prairie and Fitchburg don't require it. Middleton requires the owner to live in the house or the ADU at least 10 months a year, Verona requires the owner to live in the main house, and Dane County requires the owner to live in one of the two units.
Does a basement apartment count as an ADU?
In Madison, Middleton, Fitchburg, Sun Prairie and Verona, yes. Under the state building code it turns the house into a two-family dwelling, which means fire-rated drywall between the units, 20-minute fire-rated doors between them, and exits of its own, usually an egress window in each bedroom.
How much does an ADU cost?
Madison city staff wrote in 2024 that a detached ADU commonly costs $200,000 to $300,000. On top of construction come town fees: in Madison a $100 site plan review and a $5,026.88 park impact fee (2026), plus building permits. A basement or garage conversion usually costs less than a new building because the foundation and shell are already there.
Can I rent out my ADU on Airbnb?
Usually only with limits. In Madison, if you live in the main house you can't rent the ADU for stays under 7 nights; stays of 7 to 29 nights are allowed up to 180 days a year with a permit. Verona allows short-term rental only in the owner's primary residence, for stays of 7 to 180 days.
Does Wisconsin have a state ADU law?
No. A 2025 bill (AB 449) would have made one ADU a permitted use on every residential lot with a single-family house, but it failed when the session ended on March 23, 2026. Each town sets its own rules.
Will an ADU raise my property taxes?
Yes. Wisconsin assesses property at full market value as of January 1, and assessors are told to inspect properties that get building permits. An ADU is assessed like any other improvement.
Building an ADU with us
Turning a basement, attic or garage into an ADU is remodeling work: basement finishing, framing and insulation, plus the fire separation, exits and utilities that make it a legal second home. When we quote one, we start with the zoning check and plan the build around the inspections.
Zoning rules change: Madison's ADU rules changed seven times between December 2021 and October 2025. We checked each town's code and records in October 2026 and linked the sources. Confirm with the zoning office before you design. This is a guide, not legal advice.