Accessory dwelling units are now one of the fastest ways to add living space, house family, or create rental income across the Portland metro and Clark County. The rules differ meaningfully between Oregon and Washington, and 2026 brought changes worth understanding before you design anything.
Portland, Oregon ADU rules
Oregon has some of the most ADU-friendly legislation in the country. Portland permits detached backyard cottages, garage conversions, basement ADUs, attached units, and above-garage builds on most residential lots. System development charges have been a major cost lever, so confirm current SDC exemptions before budgeting.
- Detached new construction on most residential lots
- Garage and accessory structure conversions
- Basement and internal conversions
- Attached units sharing a wall with the primary home
Vancouver, WA and Clark County ADU rules
Washington has expanded ADU allowances statewide, and Clark County jurisdictions have followed. Vancouver permits both attached and detached units, with size, height, and setback limits that vary by zone. Utility connections and metering are the most common source of surprise cost.
The permitting timeline, not the construction timeline, is what usually determines when an ADU is finished.
How long approval takes
Plan on several months from first drawing to issued permit in either jurisdiction, longer if the site needs variances or utility work. Building the drawings around what is already allowed is the single biggest schedule saver.
What it costs to build
Most ADU projects land between $80,000 and $250,000 depending on size, foundation, and finish level. See our pricing guide for full ranges, or our ADU construction service for what a complete scope includes.
Building in a specific city? We work throughout Vancouver, Portland, Camas, and Washougal. Request a free estimate to talk through your lot.