FAQ
Common Questions
About ADUs
Straight answers about ADU cost, permitting, zoning, and what the process actually looks like in Madison, WI and Dane County.
How much does an ADU cost in Madison, WI?
ADU costs in Madison and Dane County typically start in the low-to-mid $100,000s for a detached unit, depending on size, complexity, and finish level. Garage ADUs — an ADU above a new detached garage — and attached ADUs can be priced differently than new detached construction. We provide a ballpark cost estimate during the free feasibility check, and fixed pricing before contract signing.
How long does it take to build an ADU?
From your first call to Certificate of Occupancy, most ADU projects in Dane County take 4 to 6 months. The timeline includes feasibility (1–2 weeks), design (4–6 weeks), permitting (4–12 weeks, depending on the municipality), and construction (8–16 weeks). Permitting is often the longest variable — we manage this process for you and respond to any plan review comments on your behalf.
Do I need a permit to build an ADU in Wisconsin?
Yes. All ADUs in Wisconsin require a building permit, and in most municipalities, zoning approval as well. Permit requirements vary by city and township — Madison's process differs from Fitchburg's, which differs from Mount Horeb's. We prepare and submit all permit applications. You don't deal with the municipality — we do.
Can I rent out an ADU in Madison, WI?
Yes. In Madison and most Dane County municipalities, you can rent your ADU to a tenant. Some municipalities have owner-occupancy requirements — meaning you must live on the property (either in the main house or the ADU) while renting the other unit. We flag any municipality-specific restrictions during your feasibility check.
What's the difference between an ADU and a tiny home?
The terms are often used interchangeably. An ADU (Accessory Dwelling Unit) is the legal and zoning designation for a second, self-contained dwelling on a residential lot. A tiny home refers to a smaller-than-average living space. When built on a foundation and permitted as an ADU, a tiny home and an ADU are the same thing. We use both terms — ADU is the code term, tiny home is how most people describe what they're envisioning.
Do I need to live on the property if I have an ADU?
It depends on your municipality. Madison does not require owner-occupancy — you can rent your ADU without living on-site. Many other Dane County municipalities do require it, including Middleton, Fitchburg, and Mount Horeb (where a recorded covenant is required per its March 2026 ordinance). We review the current requirement for your specific address during the feasibility check.
Can I build an ADU on my lot in Dane County?
Most single-family and two-family residential lots in Dane County are eligible for an ADU, but eligibility depends on your zoning district, lot size, setbacks, and municipality. The fastest way to find out is the free feasibility check — we review your address and give you a definitive answer.
What's included in a Boundless Tiny Home?
Every ADU we build includes architectural design, full permitting, mini-split HVAC, all appliances, quartz countertops, luxury vinyl flooring, slow-close cabinetry, French entry doors, and a lifetime composition roof. No allowances, no finish-it-yourself situations. What you see in the contract is what gets built.
What is a Certificate of Occupancy (CO)?
A Certificate of Occupancy is the final permit issued by your municipality that certifies your ADU was built to code and is safe and legal to occupy. Every Boundless project is delivered to CO — it's the standard we hold ourselves to on every build.
Can I put an ADU on a corner lot or oddly shaped lot?
Possibly — corner lots and irregular lots often have different setback requirements and may have more or less flexibility than standard lots. We analyze your specific parcel during the feasibility check and identify any constraints or opportunities.
Will an ADU affect my property taxes?
Yes — adding an ADU increases your assessed property value, which increases your property tax bill. The amount depends on the finished value of the ADU as assessed by your municipality. The tax increase is typically modest relative to the rental income an ADU generates. We can walk through realistic projections during your feasibility check.
Can I sell an ADU separately from my main home?
In most cases, no — not as-built. A standard ADU is legally part of your primary parcel and cannot be sold separately without a condo conversion or lot subdivision, both of which require municipal approval and are generally difficult to execute in Wisconsin. A condo conversion is legally possible in some situations. We have a full blog post on this topic if you want the specifics.
What happens to the ADU when I sell my house?
It transfers with the property. The ADU is a permanent structure on your lot — when you sell the home, you sell both. This is actually a selling advantage: properties with income-generating ADUs typically command a premium, and buyers can finance based on the combined income potential. If your municipality requires owner-occupancy, that covenant transfers to the buyer as well.
Can my HOA prevent me from building an ADU?
Possibly. HOA covenants operate separately from municipal zoning — even if your city permits ADUs, your HOA may restrict them. Wisconsin law does not currently preempt HOA restrictions on ADUs the way some states do. Review your CC&Rs before moving forward. We can help you identify what to look for, and we discuss HOA status during every feasibility check.
What's the difference between a permitted ADU and one that requires a Conditional Use Permit?
A permitted ADU is allowed by right — if you meet the code requirements, the building permit gets approved. A Conditional Use Permit (CUP) means your project goes before a plan commission or zoning board for discretionary approval. CUPs add 4–8 weeks, some cost, and a degree of uncertainty. We handle CUP applications as part of our permitting service.
Can I use my ADU as a short-term rental (Airbnb)?
It depends on your municipality. Madison requires a short-term rental license and has rules about host presence and maximum nights per year. Other municipalities restrict short-term rentals more aggressively. Income potential is higher with short-term rental, but so is the operational complexity. We have a full blog post covering Airbnb rules for ADUs in Madison.
Does an owner-occupancy requirement prevent me from renting the ADU?
No. Owner-occupancy requirements mean you must live somewhere on the parcel — in either the main house or the ADU — but they do not prevent you from renting the other unit. If you live in the main house, you can freely rent the ADU. What they prevent is owning the property purely as an investment without living on-site.
How do utilities work for an ADU?
ADUs can share utilities with the primary residence or have separate meters. Shared utilities are simpler and cheaper upfront but make it harder to bill tenants accurately. Separate meters are better for long-term rental situations since tenants pay their own bills, but adding a meter has upfront connection costs. We evaluate utility strategy as part of every project design.
Have a question not answered here? Call us at 608-400-0121 or request a feasibility check and we’ll answer it directly.
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