The ability to build two ADUs on a single residential lot in Madison was once theoretical. Madison’s zoning updates have made it practical — for lots that qualify. If you’re a Madison homeowner with a larger lot, this changes the investment calculus significantly.
What Madison Now Allows
Under Madison’s updated zoning code, properties in qualifying residential districts can have up to two ADUs in addition to the primary residence — three total dwelling units on one lot. This can be achieved through any combination of attached and detached ADUs, subject to specific rules for each type. Qualifying districts include TR-C2, TR-V2, TR-V3, and certain mixed residential designations. Single-family base zones (TR-C1, SR-C1) may allow two ADUs on larger lots — verify current code for your specific zoning district, as allowances have been updated multiple times in recent years.
Lot Size Requirements
This is where the opportunity narrows. Madison sets minimum lot area requirements for two-ADU properties. A standard 50x120 foot urban lot may not meet the threshold for a second ADU even if the zoning district permits it in principle. Properties that make sense for two ADUs tend to be corner lots with more usable backyard, large interior lots (8,000+ square feet) in transitional neighborhoods, or properties that were originally double lots or assembled parcels.
Construction Sequencing
You don’t need to build both ADUs simultaneously. Many owners build the first, stabilize it through rental or family use, then assess whether a second makes sense. The second permit application happens separately. Building both at once creates some construction efficiencies — shared utility trench costs, mobilization savings — but it’s double the capital outlay at one time. The phased approach is more common and often more practical.
The Financial Math
A two-ADU property in Madison at current market rates: ADU 1 at $1,400–$1,600/month, ADU 2 at $1,300–$1,500/month. Combined gross income $2,700–$3,100/month. Against a two-ADU build cost of $250,000–$350,000, gross yield runs approximately 10–14% annually. After vacancy, maintenance, and insurance, net yield is lower — but the long-term picture includes property appreciation and the ability to house family in one unit while renting the other. A well-positioned Madison property with two permitted, income-generating ADUs commands a meaningful premium over an equivalent property with one or none.
The first step is a site assessment. We look at lot dimensions, zoning, existing structure placement, utility locations, and setback constraints to tell you whether a second ADU is feasible and what it can look like. Start with a free feasibility check.