Accessory dwelling units (ADUs) are a unique way to add housing to an area. To increase both the amount and type of available housing, Madison has made it easier to build ADUs. An ADU is now a permitted use on the lot of an owner-occupied, single-family home.

You need permits to build any ADU. These steps are for an ADU that you are creating:

  • by adding an addition of new square footage to your single-family home OR
  • from an existing space in a single-family home through remodeling, such as a basement or attic.


There are different steps to build a detached ADU.
Basic information

  • ADUs can be up to 900 square feet in size and have up to two bedrooms. Different types of ADUs have different requirements.
  • To get an ADU approved, you first need site plan approval.
  • Engineering will assign a new address for the ADU.
  • By law, either the ADU or the main house must be owner-occupied.
  • You must pay a Parks Impact fee for a new ADU. The fee is about $4500. Check with Parks for the current rate for ADUs.
  • You will need licensed contractors to obtain permits and complete the work.

Utility connections

  • Plumbing code: You must add a restriction to the deed if both the primary home and the ADU are on the same sewer lateral. If you want to sell the buildings separately, a contractor will have to separate the sewer.
  • From Madison Water Utility: the water lateral may not be able to serve both homes. If it is large enough, a plumbing contractor may extend the water lateral. A contractor needs to calculate the water supply based on the number of fixtures and the pressure drop. Water Utility prefers to have only one meter per parcel. If you need or want separate meters, you will need to run a new service from the street.
  • Madison Gas and Electric: each home on a lot must have its own meter and electrical service per parcel. The owner may need to pay for a new riser and wiring to the meter.


At any time during the planning or construction of your garage, you can call Building Inspection if you have questions. We are happy to answer your questions and suggest solutions to your problems.

Process Overview

  1. Check with Zoning

    Before you get started, make sure that your plan is doable. Zoning staff will explain your constraints given your lot dimensions and characteristics. Call (608) 266 4551, ext. 3.

  2. Preliminary Zoning review and site plan submittal

    By this point you'll have hired a contractor. Next, make an appointment with Zoning to discuss your site plan materials.

    At your appointment, Zoning will do a preliminary review for your project. Zoning will see if your application is ready to submit or if you need to make changes. Zoning will review the following requirements:


    • Up to 900 square feet of living space.
    • Two bedrooms, at most.


    • Must meet the setback requirements for your home.
    If your lot is on a corner or irregularly shaped, you might have increased setbacks. Show your site plan to city Zoning staff to find out where you can build your ADU.


    With these requirements in mind, make a drawing (site plan) of your lot (PDF). The site plan drawing must show:

    • All existing and proposed structures.
    • The dimensions of the lot, the ADU, the house, and any other structures.
    • The distances from the ADU to the lot lines and the distances to all other structures.

    Draw your site plan to scale. A scale of 1 inch = 20 feet works well.

    Make sure you bring the following to your appointment:

    • A site plan.
    • Elevations.
    • A floor plan of the ADU.

    All these drawings should be to scale.

  3. Submit for site plan review

    After making any required changes, submit by email the three plans from above.

    Various city agencies will review the plans for compliance. Make sure you respond to any requirements from City agencies. If you do not respond, it will delay the process. When it's time, Parks will contact you to pay the Park Impact fee. City Engineering will assign the ADU an address.

    This step can take two to three weeks. Once the agencies finish the site plan review, you will receive an email.

  4. Apply for permit(s)

    The City charges for permits to cover the cost of plan review and on-site inspections. Schedule an appointment with the Permit Counter. Licensed contractors must apply for the permits.

    What to bring

    For the building permit, bring all the items on this list.

    The initial plan review will take 10 – 15 business days.

  5. Obtain permits

    Once we finish plan review, contractors need to pay for the permits and pick up plans.
    You need issued building and plumbing permits before work begins. You need the electrical and HVAC permits before you start that work. Display the permits so they are visible from the street.


    Where to go

    Building Inspection Permit Counter by appointment only
    Madison Municipal Building
    215 Martin Luther King Jr. Blvd Suite 017
    Madison, WI 53703

  6. Call for inspections

    Once we issue your permit, we will give you the name and phone number of the inspector for your area. The Building Inspector will work with you to be sure the work is done correctly.

    Inspections make sure that the materials and the work are up to code. If any work does not pass inspection, you must correct it and call for a reinspection. All permits must have approved Final inspections.

  7. Completion

    Once the work is done and approved, your permits are closed. We will then issue a Certificate of Occupancy.

Related Forms & Handouts