Attached ADUs by Boundless Tiny Homes
Boundless Tiny Homes offers attached accessory dwelling unit construction for homeowners in the Madison, Wisconsin area. An attached ADU connects directly to the primary residence, sharing one wall while functioning as a fully independent living unit. It includes its own exterior entrance, kitchen, bathroom, and living area — operating as a permitted dwelling unit rather than simply a home addition.
This type of ADU is a practical option for properties where setbacks or limited yard space make a detached structure difficult to build. Because one wall is shared with the existing home, construction costs can be lower compared to a detached ADU, and the permitting process may move more quickly.
Who Typically Builds an Attached ADU
Attached ADUs serve a range of household needs. Some of the more common use cases include:
- Aging parents: Providing a parent with their own space on the same property, allowing for proximity while maintaining independent living.
- Multigenerational households: Extended family members can live together without sharing the same front door or living areas.
- Rental income: Attached ADUs in walkable Madison neighborhoods can attract tenants who prefer the feel of a house over an apartment unit.
- Limited lot size: For properties without sufficient yard space for a detached structure, an attached addition may be the only viable path to adding a second unit.
Boundless Tiny Homes conducts a feasibility check to confirm what is buildable on a given property before any design or construction work begins.
Project Details and Process
Attached ADU projects handled by Boundless Tiny Homes typically fall within the following parameters:
- Size range: 300 – 700 sq ft, depending on the addition
- Project timeline: 4 – 6 months from start to Certificate of Occupancy
- Foundation: Tied to the existing structure
- Separate entrance: Required for ADU designation
- Energy code: Fully compliant with Wisconsin energy code
- HVAC: Mini-split system, standard
These figures can vary based on lot conditions, municipality requirements, and design choices. The feasibility check establishes the specifics for each individual property.
The construction process follows a defined sequence. It begins with a feasibility and design brief to confirm what is buildable and establish scope, size, and budget. Architectural design follows, covering floor plans, elevations, and material selections. Boundless Tiny Homes then manages all permit submissions with the relevant municipality. Construction covers site work through final finishes, with full project management throughout. The process concludes with a final inspection and Certificate of Occupancy issuance.
For homeowners considering an attached ADU — whether as an in-law suite, a granny flat, or a rental unit — Boundless Tiny Homes offers a free feasibility check to review the property address, zoning, and lot conditions before any commitments are made.