Oregon ADU (accessory dwelling unit) Rules in 2026: A Practical Guide for Homeowners

Many single-family lots inside Oregon cities can have an accessory dwelling, subject to local siting, design, utility, and permit rules. The state sets the floor, and each city sets its own fees and details.

The statewide framework

Inside an urban growth boundary: ORS 197A.425 requires cities with more than 2,500 residents and counties with more than 15,000 residents to allow at least one ADU for each detached single-unit dwelling in qualifying zones. Local siting and design requirements still apply.

For ADUs covered by that provision, local regulations cannot require the owner to occupy either dwelling or require construction of additional off-street parking. The statute does let local governments regulate vacation occupancy differently, including with owner-occupancy or parking conditions, so check the local rules before you count on short-term rental income.

Outside an urban growth boundary: the urban allowance doesn’t apply automatically. ORS 215.495 lets counties adopt a rural residential ADU program with conditions, but it doesn’t require one. Check whether your county has adopted a program, and look at resource-land restrictions, water supply, wastewater, and fire access. Historic-home conversions have a separate statutory path.

Additional homes or separate ownership: middle-housing and land-division rules are separate from a basic ADU approval. Ask the city or county which housing type and approval path apply before you plan multiple units or a separate sale.

System Development Charges

System Development Charges (SDCs) are infrastructure charges that a city or service district may assess when adding a dwelling. They’re separate from construction costs and can make a big difference in the budget.

SDCs vary by city, service provider, and project, and a waiver in one city doesn’t tell you what the next city over charges. Ask for a current, itemized estimate that shows:

• The city and utility districts assessing the project.
• Water, wastewater, stormwater, park, and transportation charges that apply.
• Any available waiver, its application requirements, and charges it does not cover.

Get that estimate before you commit to a design. In your budget, keep agency fees separate from Wolf’s permitting service and the connection work on site.

Portland metro fees and waivers

Portland has a separate ADU SDC waiver. Qualifying residential ADUs can apply through the city’s Revenue Division. The recorded covenant prohibits short-term rentals throughout the property, including the main house and individual bedrooms, for 10 years from final inspection approval. Review the ADU waiver instructions before counting on the savings.

The temporary housing exemption does not cover ADUs. Ordinance 192082 established a separate program for eligible housing permits issued August 15, 2025, through September 30, 2028. Portland Code 17.14.070 J expressly excludes accessory dwelling units. For an ADU, the waiver under subsection F, with its covenant, is the program to look at.

Check each city and service district. Beaverton, Gresham, Hillsboro, Oregon City, Tigard, and Tualatin each set their own SDC schedules and design standards. A Portland rule usually doesn’t apply across a city line or across the river.

SW Oregon and the rest of the delivery range

South and west of the metro, check the property’s jurisdiction and whether it’s inside an urban growth boundary before you lean on the statewide rules. Salem, Corvallis, Eugene, and the coastal towns have their own fee schedules and siting rules, and the local review covers the dwelling, utilities, setbacks, height, and overlays before you pick a model.

Permitting steps, setbacks, and height

The typical path looks like this:

1. Zoning and feasibility check: confirm your lot is eligible, and find the setbacks, height limit, lot coverage, and maximum ADU size for your zone. There’s no statewide set of ADU dimensions; they all come from the local code.
2. Land use review, if your city requires one for ADUs. Many treat them as a permitted use with no discretionary review.
3. Building permit: structural, plumbing, mechanical, electrical, and the site work (foundation, utility connections).
4. SDC assessment: the fees get calculated here, and any waivers or exemptions get applied.
5. Inspections and final occupancy.

How modular approvals work

The Oregon Building Codes Division’s Prefabricated Structures Program reviews qualifying factory construction. Its approval and insignia cover the building itself. They don’t decide whether zoning allows the home on your lot, and they don’t give you permission to move in.

Local review covers site design, the foundation, accessibility where it applies, utility connections, installation, and any work finished on site. Final occupancy comes after the required inspections. The state insignia is not a certificate of occupancy.

An approval from another state isn’t automatically an Oregon approval. The program can also authorize the final inspection and the insignia at the installation site, so the tag isn’t always on the home when it leaves the factory.

How Wolf handles Oregon projects

Wolf builds in Battle Ground and coordinates the home and site approvals for your property. Before we schedule delivery, we confirm the model, the state approval documents, the foundation design, utilities, and the local permit scope.

We also handle the in-house permitting for Oregon and Washington projects. We pull the zoning, run the SDC numbers for your specific city, and file the paperwork, including the Portland SDC waiver documents when they apply. We check feasibility early. If the project can’t be permitted, your signed permitting agreement spells out the refund and what it excludes, so read those terms before you pay the permitting service fee. SDCs and local design rules decide whether most backyard cottages pencil out, which is why we pin them down first.