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

Many single-family lots inside Oregon cities can support an accessory dwelling, subject to local siting, design, utility, and permit requirements. Fees and implementation vary by city. Below are the statewide rules and the local details to confirm in 2026.

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 allows different regulation of vacation occupancy, including owner-occupancy or parking conditions. Confirm the intended use before relying on rental income.

Outside an urban growth boundary: the urban allowance does not apply automatically. ORS 215.495 lets counties adopt a rural residential ADU program subject to conditions; it does not require every county to allow one. Check the county’s adopted program, 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. Have the jurisdiction confirm the permitted housing type and approval path before planning 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 are separate from construction and can materially affect the project budget.

SDCs vary by jurisdiction, service provider, and project. A waiver in one city does not establish the fees for a neighboring property. Request a current, itemized estimate that identifies:

• 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 committing to a design. Keep agency fees separate from Wolf’s permitting service and field connection work so the budget reflects each part of the project.

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. An ADU owner should evaluate the ADU waiver under subsection F, including its covenant, rather than assume the temporary housing program removes those conditions.

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

SW Oregon and the rest of the delivery range

South and west of the metro, confirm the property’s jurisdiction and urban growth boundary before relying on the statewide framework. Salem, Corvallis, Eugene, and coastal communities have their own fee schedules and siting requirements. A local review needs to address the proposed dwelling, utilities, setbacks, height, and applicable overlays before model selection.

Permitting steps, setbacks, and height

The typical path looks like this:

1. Zoning/feasibility check - confirm your lot is eligible, find the setbacks, height limit, lot coverage, and maximum ADU size for your zone.
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 - this is where the fees get calculated and where waivers/exemptions get applied.
5. Inspections and final occupancy.

Confirm the adopted size, height, setbacks, lot coverage, and design requirements for your zone. There is no single set of statewide ADU dimensions to use for every property.

How modular approvals work

The Oregon Building Codes Division’s Prefabricated Structures Program reviews qualifying factory construction. Its approval and insignia establish the approved building scope; they do not establish zoning eligibility or permission to occupy the home on a particular lot.

Local review still covers site design conditions, foundations, accessibility where applicable, utility connections, installation, and any authorized work completed on site. Final occupancy approval follows completion of the required inspections. The state insignia is not a certificate of occupancy.

Confirm the approval path for the selected home and destination. An approval from another state is not automatically an Oregon approval. The program can also authorize final inspection and attachment of the insignia at the installation site, so an exterior tag attached before transport is not a universal rule.

How Wolf handles Oregon projects

Wolf builds in Battle Ground and coordinates the applicable home and site approvals for the destination. Confirm the selected model, state approval documents, foundation design, utilities, and local permit scope before scheduling delivery.

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 coordination of the Portland SDC waiver documents when it applies. We review feasibility early. If the project cannot be permitted, your signed permitting agreement defines the eligible refund and exclusions. Review those terms before paying the permitting service fee. SDCs and local design rules decide whether most backyard cottages pencil out, so we pin them down first.

This is general information from Wolf Industries, not legal advice. Recheck the current statute, local code, and SDC schedule before you file. Cities amend waivers and fee tables.