Thinking about adding an accessory dwelling unit to your Oregon property? You’re not alone. With housing costs climbing and the need for flexible living arrangements growing, many homeowners are exploring ADUs as a smart investment.
But before you can break ground, you’ll need to navigate Oregon’s permit requirements, which have evolved significantly since 2018 when the state made ADUs legal by right on most residential properties.
Key Takeaways
- Oregon allows ADUs by right on all residential properties statewide, but local jurisdictions control permitting processes and fees
- Most ADU applications follow a Type I Land Use review process that takes about two weeks for approval
- Building permits are mandatory for all ADU construction, with costs ranging from over $1,000 to potentially $20,000+ depending on system development charges
- No off-street parking is required statewide, and owner-occupancy isn’t mandatory in most areas
- Pre-approved plans are available in many cities to streamline the permit process
Oregon’s ADU Revolution: What Changed in 2018
As of July 1, 2018, ADUs are allowed by right on all residential properties within most Oregon cities and counties. This represents a major shift that makes building ADU projects more accessible than ever before.
Don’t mistake “allowed by right” for “no permits required.” Each jurisdiction maintains its own permitting process and can set specific fees and development requirements.
The Two-Part Permit Process:
- Land Use Approval – Most ADUs qualify for streamlined Type I review
- Building Permits – Required for all construction or conversion projects
Most ADUs go through a Type I Land Use review, which is quick and straightforward, usually wrapped up in about two weeks. The heavier lift comes during the building permit phase, where you’ll deal with everything from plumbing and wiring to structural updates.
Different ADU Types, Different Permit Paths
Working with a garage, basement, or attic conversion? You’ll typically need building permits for:
- Electrical work to meet residential code
- Plumbing installations and connections
- Mechanical systems for heating and ventilation
- Structural modifications for proper egress
However, bringing older spaces up to current residential code often reveals unexpected challenges.
New Detached Construction
Building from scratch requires more comprehensive permitting. This includes site planning, foundation work, full building systems, and utility connections. Applying for an ADU permit involves submitting a building permit application, site plan, and architectural drawings.
Some cities offer pre-approved plans that can significantly speed up approval. Portland’s pre-approved detached ADU plans can expedite the review process.
Size and Location Requirements That Matter
Oregon’s statewide rules provide consistency, but local jurisdictions add their own requirements. Understanding both levels helps you plan effectively.
Statewide Requirements:
- Detached ADUs must be located behind the primary residence or 40 feet from the street if in front
- No off-street parking required anywhere in Oregon
- No owner-occupancy requirements in most areas
Size limitations vary significantly by jurisdiction. Most areas cap ADUs at a percentage of the primary dwelling’s square footage or set absolute limits. Some counties like Deschutes require lawfully established ADUs to be located no farther than 100 feet from the primary dwelling. The parking elimination represents a huge win for homeowners.
The Money Talk: Permits and Fees
Permit costs can vary dramatically across Oregon jurisdictions. While building permits themselves might cost over $1,000, the real wildcard is system development charges (SDCs).
Impact fees or system development charges vary widely among local communities. Some communities waive these fees entirely, while others charge fees of $20,000 or more per ADU.
Fee Variation Examples:
- Salem City Council has waived SDCs for ADUs entirely
- Some jurisdictions maintain substantial charges of $15,000+
- Others offer SDC waivers based on specific circumstances
Research your local SDC policies early in planning. They can dramatically affect project feasibility and should factor into your budget from day one.
Your Step-by-Step Permit Roadmap
Most jurisdictions follow a similar pattern, though specific requirements vary.
Step 1: Connect with Local Planning
Begin by contacting your local planning department for current requirements and fee schedules. Many cities offer free 15-minute appointments where you can meet with city planners about zoning requirements or building code reviewers about engineering needs.
Step 2: Gather Required Documents
You’ll typically need:
- Completed building permit application
- Detailed site plan showing property boundaries and proposed ADU location
- Architectural drawings with floor plans and elevations
- Any jurisdiction-specific forms or studies
Step 3: Navigate the Review Process
Standard projects usually move through administrative review quickly. However, ADUs in historic districts or environmental zones may require Type II or Type III review, taking longer for approval.
Building Code Compliance Beyond Basic Permits
Your ADU must meet the same building codes as any residential structure. This creates non-negotiable requirements across several areas.
Essential Compliance Areas:
- Proper egress requirements for emergency exit
- Electrical systems meeting current code standards
- Plumbing connections to approved sewer systems
- Heating systems maintaining adequate temperatures
Fire safety requirements deserve special attention. While not all jurisdictions require sprinkler systems in ADUs, installing them provides safety benefits and potentially reduces insurance costs.
Setting foundation for ADU work requires attention to soil conditions and drainage. Poor site preparation leads to foundation problems, making proper permits and inspections crucial for long-term success.
Local Variations Across Oregon
While state law establishes the framework for ADU laws, individual cities and counties implement specific requirements. Understanding your local landscape makes the difference between smooth approval and extended delays.
Portland has one of the most developed ADU programs with streamlined processes and pre-approved plans. Salem offers free ready-build plans for download and has eliminated SDCs entirely.
Rural counties face different considerations around septic systems, well water, and fire access that urban areas don’t encounter. These factors can significantly impact both permitting requirements and construction costs.
The concept of accessory dwelling units continues evolving as jurisdictions gain implementation experience. Some areas still use traditional terms like mother-in-law unit, but permitting requirements remain similar regardless of terminology.
Planning for Long-Term Success
ADUs are intended for permanent housing, not temporary or seasonal use. Consider how an ADU can increase property value while planning your permit strategy. Well-designed ADUs meeting all code requirements typically add more value than projects cutting corners on permits or construction quality.
Ready to start your ADU project? Explore professional ADU construction services that handle the entire process from permits through completion, ensuring your project meets all Oregon requirements while maximizing your investment potential.
Moving Forward with Confidence
Building an ADU in Oregon offers tremendous opportunities thanks to progressive state laws supporting this development type. Success depends on understanding and following proper permitting procedures that vary significantly by jurisdiction.
While the process might seem complex initially, Oregon’s streamlined approach makes ADU development more accessible than in many other states. Start by researching local requirements, consider pre-approved plans where available, and seek professional guidance when needed.
With proper planning and attention to permit requirements, your ADU project can provide valuable housing while delivering strong returns on your investment.
