One of the details that surprises homeowners mid-project: your ADU needs its own address. Not a unit number appended to your existing address — a separate, official address registered with the city’s 911 system. Here’s how it works in Madison, when it happens in the process, and why it matters more than most people expect.
Why a Separate Address Is Required
The requirement isn’t bureaucratic convenience. Emergency services need to be able to locate a structure quickly. If your main house is 1234 Oak Street and your ADU is in the backyard, a 911 dispatcher needs to send help to the right building. A shared address creates ambiguity that can cost time in an emergency.
Madison’s Engineering Division assigns ADU addresses as part of site plan review — Phase 1 of the permit cycle — before building permits are issued. Your ADU address is established relatively early in the process, not at the end.
How the Address Assignment Works
During site plan review, Madison’s Engineering staff assigns an address based on the ADU’s physical location on the lot and its primary entrance orientation. If your ADU fronts an alley, it typically gets an alley address. If the entrance faces a side street, same logic applies. If it’s a backyard ADU with an entrance facing the main street, the address will likely be a variant of your primary address — but the specific format depends on the block and how Engineering handles the street sequence.
You don’t choose the address. Engineering assigns it based on mapping conventions. Some homeowners are surprised when the ADU gets an address from a different street than the primary residence. This is correct and working as designed.
What the Address Affects
Once assigned, the ADU address becomes the official address for utility connections (when doing separate metering), mail delivery, rental listings, insurance policies, and property records. The ADU address is associated with your parcel in the city’s records but remains part of the same parcel as the primary residence unless you pursue a legal subdivision.
Timing in the Permit Process
Address assignment happens during site plan approval, which typically takes 4–8 weeks in Madison. You won’t have the address before submitting for site plan review. This matters if you’re trying to establish utility accounts or set up rental listings before the permit process completes.
Outside Madison
The process varies in surrounding municipalities. Fitchburg, Middleton, and the Town of Verona each handle address assignment differently, and some smaller municipalities route it through the county. If your ADU is outside Madison city limits, ask about address assignment specifically during your pre-application meeting — it doesn’t always happen as early in the process as it does in Madison proper.
We manage the permit process for every ADU we build, handling address assignment coordination automatically. If you’re in the early stages of planning, start with a free feasibility check.