Apartment buildings along rail ways
Development Services Center
  1. Building Inspection Counter Appointments

    Building Inspection plan review and zoning review counters will be open to the public by appointment only.

New Detached Accessory Dwelling Unit

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. ADUs are now a permitted use on the lot of a dwelling with up to eight units.

You need a permit to build any ADU. These steps are for ADUs that are detached from the single family home. There are different steps for attached ADUs.

Call Building Inspection if you have questions, we are happy to help.

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.
  • 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.
  • The principal dwelling may have up to eight units.
  • You will need licensed contractors to obtain permits and complete the work.

Utility connections

Electric service and meter

Each dwelling unit must have its own electric meter and service panel.

Main Water Lateral

The existing water lateral on the site may not have the capacity to serve both buildings.

A contractor must verify that the existing water lateral is adequate. To verify, calculate the water supply based on the total number of plumbing fixtures and pressure drop. The contractor must also confirm the adequacy with Madison Water Utility.

  • If adequate: A plumbing contractor can extend the existing water lateral to the ADU.
  • If not: Upgrade the existing water lateral to a larger size. Otherwise, install a new dedicated water lateral for the detached ADU.

Water Meter

The Madison Water Utility prefers one water meter per parcel. If you would rather separate meters, you must run a new water lateral from the street to the detached ADU.

Sewer Lateral

Sewer Lateral

Depending on placement, the existing sewer lateral may not be able to serve both homes. 

A contractor must verify compliance with SPS 382.30(11)(a)2 and SPS 382.30(12)(f). These regulations govern where and how to connect sewer laterals. Deed restrictions may also be required during this process.

  • If compliant: A plumbing contractor can connect the ADU’s sewer lateral to the existing one.
  • If not: Install a new sewer lateral.

A contractor must verify compliance with SPS 382.30(11)(a)2 and SPS 382.30(12)(f). These regulations govern where and how to connect sewer laterals. You may need to file a deed restriction as part of this process.

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. Call (608) 266 4551, ext. 3 for more information.

  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:

    Size

    • Up to 900 square feet of living space.
    • At most, two bedrooms.

    Placement

    • An ADU must be at least three feet away from your house and other structures.
    • An ADU should be at least three feet from the rear or side lot lines of your yard.
    • An ADU located behind your house likely meets zoning rules.
    • An ADU on the side of your house needs a setback greater than three feet from the side lot line. Check with Zoning staff for this setback distance.

    If your lot is on a corner or is irregularly shaped, the setbacks may be different than described. 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. Make sure you use an accepted scale.

    Make sure you bring the following to your appointment:

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

    All these drawings must be to scale.

    For lakefront properties, a survey prepared by a registered land surveyor is required. The survey must show existing setbacks to the Ordinary High Water Mark of buildings on adjacent lots.

  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 permits, we will give you the name of the inspectors 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.

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1 & 2 Family Residential