ADU construction costs
Explore a self-contained accessory dwelling unit with its own kitchen and bathroom. Attached, detached, and conversion projects have different construction requirements. Establish the unit type, size, utility work, and site conditions before comparing bids. This broad national range is not a Portland-specific quote.
National planning benchmark. Portland-specific prices have not yet been verified.
Your price depends on project size, materials, access, and existing conditions. Confirm the scope, permits, disposal, and exclusions with your contractor.
What the project can include
- A secondary living unit with a kitchen and bathroom.
- An attached addition, detached building, or conversion of existing space.
- Site preparation, building work, systems, and finishes for the chosen unit type.
Compare common ADU construction types
| ADU type | National planning range |
|---|---|
| Prefab modular | $80–$160 / sq ft |
| Attached | $125–$225 / sq ft |
| Detached | $150–$250 / sq ft |
| Garage conversion | $50–$200 / sq ft |
National planning benchmarks. Scope and local bids can differ.
What affects your price
- New construction versus converting an existing structure.
- Unit size and the level of site preparation.
- Access to existing utilities, layout, and finish choices.
Before you compare bids
Choose a unit type and approximate size before comparing bids. Ask contractors to itemize site work, utility connections, design, permits, and finishes. Confirm the scope for your property with a local professional.