Attached ADU — addition to an existing home in Madison, WI
Services · Attached ADUs

Attached ADU Additions: Connected to Home, Independent in Every Way.

Attached ADUs connect to your existing home while maintaining a fully independent living unit — separate entrance, kitchen, and bath. Ideal for multigenerational living without sacrificing privacy.

What Is It?

Connected to Your Home.
Independent in Every Way That Matters.

An attached ADU shares a wall with your primary residence but functions as a completely separate unit. It has its own exterior entrance, full kitchen, bathroom, and living area. From the outside, it reads as an addition. On paper, it's a permitted dwelling unit.

Attached ADUs are well-suited for lots where setbacks or limited yard space make a detached structure difficult. They often move through the permitting process more quickly, and construction costs can be lower because you're sharing one wall with the existing structure.

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Best For

Who Builds Attached ADUs

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Aging Parent
A zero-step attached home shares one insulated wall for winter access and keeps a parent thirty steps away. A care facility at $12,000–$15,000 a month drains savings with nothing left on the lot. A permanent home starting at $145K keeps that outlay as property.
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Multigenerational Household
A second unit attached to the home allows extended family to live together without crowding. Everyone has their own front door.
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Rental Income
Attached ADUs rent well — particularly in walkable Madison neighborhoods — because tenants get the feel of a house, not an apartment.
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Limited Lot Size
If your yard doesn't have room for a detached structure, an attached addition may be the only path to a second unit. We confirm during the feasibility check.
Typical Project Details

What to Expect

Size range300 – 700 sq ft (addition-dependent)
Project timeline4–6 months, not including extended permit review
FoundationTied to existing structure
Separate entranceRequired for ADU designation
Wisconsin energy codeFully compliant
HVACMini-split system, standard

Figures vary by lot, municipality, and design. Your feasibility check establishes specifics for your property.

Our Process

How We Get There

01
Feasibility + Design Brief
Confirm what's buildable. Define scope, size, and budget.
02
Architectural Design
Floor plan, elevations, and material selections for your lot.
03
Permitting
We handle all permit submissions with your municipality.
04
Construction
Site work through final finishes. Full project management.
05
Certificate of Occupancy
Final inspection, CO issuance, and project handoff.
Dusk exterior of a Boundless ADU with warm light in the windows, Madison WI
Ready to Find Out What's Possible?

Start with a Free Feasibility Check

We review your address, zoning, and lot — and tell you exactly what's buildable and what it'll take to get there.

Get Your Free Feasibility Check →