Lane County, OR ADU (accessory dwelling unit) Rules: What to Check Before You Build

In Lane County, Eugene, Springfield, the smaller cities, and unincorporated rural land all have different ADU review paths, so the first thing to settle is who has jurisdiction over your address.

If your property is inside a city, the city code and fee schedule control the local land-use side. If it is outside city limits, Lane County land-use rules may control. If the property is zoned Rural Residential and sits outside an urban growth boundary (UGB), Lane County has a specific rural ADU path tied to Oregon’s SB 391.

Who reviews your Lane County address

Inside a UGB, ORS 197A.425 requires cities over 2,500 residents and counties over 15,000 to allow at least one ADU per detached single-unit dwelling in qualifying zones. Those rules cannot require owner occupancy or extra off-street parking. That is a different framework from the rural program below. The Oregon ADU rules guide covers the statewide rules.

The county-level rural ADU path

Lane County’s public ADU page says the Board of County Commissioners passed Ordinance 23-05 on August 29, 2023 to allow ADUs on rural residential zoned properties in rural Lane County. The standards now sit in Lane Code 16.290(8). The version posted by the county is dated May 2026.

The county’s summary of the SB 391 framework includes several threshold items that matter early:

• The rural county program applies to eligible land under LC 16.290, not the separate LC 16.231 category.
• Urban reserves are excluded.
• The lot or parcel must be at least two acres.
• One single-family dwelling must already be sited on the property.
• Fire protection service, sanitation, and wastewater requirements must be addressed.
• The ADU is limited to 900 square feet of usable floor space.
• The ADU must be within 100 feet of the existing single-family dwelling.
• Vacation occupancy and land division separation are prohibited under the county’s summary.

These are initial screening conditions. The county page also includes historical SB 391 background, so check the current adopted code (below) and confirm fire requirements with Planning and the fire authority. A property can pass the basics and still need work on access, septic capacity, slopes, setbacks, and utility routing.

Official starting point: Lane County Accessory Dwelling Units.

What Lane Code 16.290(8) requires

The code defines the eligible land as property zoned Rural Residential (RR, RCP) outside a UGB that is subject to an acknowledged exception from the farm or forest land planning goals. A standard new ADU must meet all of these:

• Size: no more than 900 square feet of usable floor area. Usable floor area is measured inside the insulated exterior walls and excludes attached garages, carports, decks, stairs, porch covers, and similar appurtenances.
• Distance: no farther than 100 feet from the existing single-family dwelling, measured from a wall of the house to the nearest part of the ADU’s usable floor area.
• The house: at least one single-family dwelling is sited on the parcel, and it is not subject to a nuisance order or pending nuisance action. The county’s application says that if no house exists yet, one must be proposed at the same time as the ADU or built first.
• One ADU only, and no subdivision, partition, or other division that would put the house and ADU on separate parcels.
• Fire district: the parcel is served by a fire protection district that complies with ORS 181A.410. The applicant provides the district’s written certification, on a Lane County form, that access meets the district’s minimum requirements for emergency service.
• Evacuation plan: the applicant provides a plan with an identified route from the ADU to a staged evacuation area. If someone else owns that area, the applicant needs the owner’s written authorization. The code says county acceptance of the plan is not a certification that the plan is safe.
• Water: if a well will use exempt groundwater, no part of the parcel may be in an area where the Water Resources Commission has restricted those uses. The house and ADU count as a single unit for exempt-well purposes. The county’s application adds that a second well drilled for the ADU may not qualify as an additional exempt domestic use.
• Sanitation: the ADU complies with sanitation and wastewater rules. The county’s application says the Lane County On-Site Wastewater Program verifies compliance during the building permit process.
• No vacation occupancy: the owner records a restrictive covenant with Lane County Deeds and Records. The code defines vacation occupancy as rental for vacation purposes to an occupant with a principal residence elsewhere, for no more than 45 days.
• Area of critical state concern: no part of the parcel can be in one.

Wildfire provisions

The code also contains construction and defensible-space subsections written around the statewide wildfire hazard map. Oregon’s wildfire-map framework has changed since the ordinance was adopted. Confirm with Lane County Planning, the Building Program, and the fire district how those subsections apply to your parcel now, rather than relying on older wildfire-map references.

Setbacks and siting in the RR zone

The ADU also has to meet the RR zone’s property development standards in LC 16.290(7):

• At least 20 feet from the right-of-way of a state road, county road, or local access public road.
• At least 10 feet from all other property lines.
• At least 50 feet from the ordinary high water of a Class I stream that the Rural Comprehensive Plan designates for riparian protection. Alternative standards exist but require a separate review.

The RR standards list no zone height limit. Building code, overlays, and any other applicable review still apply. Put the 100-foot distance and these setbacks on a scaled site plan before you choose a model. On a two-acre parcel with a well, a drainfield, and a long driveway, the space that meets every rule can be smaller than it looks.

Unincorporated communities and water supply

If the parcel is inside an area the Rural Comprehensive Plan designates as an unincorporated community, the ADU needs an adequate water supply. An individual well must meet Lane Manual 9.005.160. The county’s application quotes that standard’s well-log requirement: a sustained yield of five gallons per minute over at least five hours of continuous pumping. A public or community system must provide evidence that it can serve the ADU.

Converting a historic home

Lane Code offers a second rural path for older houses. If a single-family dwelling built between 1850 and 1945 is on the parcel, the owner can build a new single-family dwelling and convert the historic home to the ADU once the new house is complete. The general conditions still apply, including two acres, no urban reserve, and sanitation. The code adds limits:

• The converted ADU cannot be altered, renovated, or remodeled to exceed 120 percent of the historic home’s usable floor area when construction of the new house began.
• It cannot be rebuilt if it is later deemed a dangerous building after fire or other damage. The owner records a covenant saying so.

The county’s application asks for evidence of when the historic home was built, such as assessment, permit, or land use records.

How a Lane County rural ADU is approved

LC 16.290(8) uses a Type I application under Lane Code Chapter 14. The county’s form calls it a complex zoning determination. It says the decision is based on objective evidence, is not a land use decision, and is not subject to public notice. The application asks for:

1. Proof of ownership, the assessor’s map and tax lot, and a written narrative addressing each standard.
2. A scaled site plan showing the house, the ADU, the 100-foot measurement, setbacks, driveways, wells, septic, and any Class I stream.
3. A scaled floor plan of the ADU showing usable floor area.
4. The fire district certification and the evacuation plan, including the staging-area owner’s authorization if needed.
5. Well information if the parcel is in an unincorporated community.

Several standards become conditions of approval, including the covenant, the one-ADU limit, and the no-division rule. Building, septic, and other permits follow the zoning determination.

The version of the form linked from the county page is dated 2023. Ask the Planner on Duty whether a newer version applies before you file.

City and county lots follow different rules

Many Lane County homeowners are not covered by the county’s rural ADU program. Eugene, Springfield, Cottage Grove, Florence, Junction City, and other incorporated areas may have their own land-use standards, system development charges, utility requirements, and inspection processes.

A Eugene ADU and a rural Lane County ADU should not be priced from the same assumptions. The model might be the same, but the permit path, fees, delivery plan, and site work can be very different. Local notes for city lots:

• Eugene
• Springfield
• Florence

Tiny homes, guest houses, and RVs

Three things that look like ADUs are not ADUs under Lane Code:

• Tiny homes on wheels. Lane County’s tiny-home guidance treats units on a frame or chassis as vehicles rather than residences and says they cannot be placed permanently. A permanent tiny home must meet Oregon building code on an approved foundation.
• Guest houses. The RR zone allows a separate guest house or accessory residential structure of up to 850 square feet with no kitchen. The ADU section does not apply to guest houses, and the guest house rules do not apply to ADUs.
• Rental RVs. Lane Code has a separate, narrower provision for one RV used as a rental dwelling on rural residential land. It is not an ADU approval.

What Wolf checks first

For a Lane County project, we usually want to know:

1. Is the parcel inside a city, inside a UGB but outside city limits, or rural?
2. Is it zoned RR under LC 16.290, outside an urban reserve, and at least two acres?
3. Is there an existing lawful single-family dwelling, or will one be built with the ADU?
4. Can the ADU sit within 100 feet of the house while meeting the 20-foot road and 10-foot property-line setbacks and staying clear of the well and drainfield?
5. Will the fire district certify access, and where is the staged evacuation area?
6. Can the property support the ADU’s septic, water, and electrical needs?
7. Can a modular unit be delivered, staged, and set safely?

We answer these before finish selections. A backyard cottage that looks right on paper can still fail on access, utilities, or local review if nobody checks the address early.

Modular homes in Lane County

Wolf homes are built in our Battle Ground factory to residential building code and delivered into Oregon as modular structures through Oregon’s prefabricated-structure process. They are not HUD code (the federal standard for manufactured homes) manufactured homes. The BCD guide for local building departments explains the split. The state program reviews the building itself. The local building department permits and inspects the foundation, utility connections, and installation, then issues the certificate of occupancy. The state insignia is not a certificate of occupancy.

Lane County or the local city still approves the site-specific pieces. Planning in Florence or elsewhere on the coast? See Oregon coast ADUs and beach cottages.

Start with the address

If you are planning an ADU in Lane County, send us the property address and intended use. We will start with jurisdiction, zoning, access, utilities, and model fit.

For the statewide background, read our Oregon ADU rules guide. For model fit, compare the Wolf model lineup. For budgeting, see ADU costs and the Oregon ADU cost guide. When you are ready, request a property evaluation.

This is general information, not legal advice. Confirm current rules, fees, and application requirements with Lane County or the city that has jurisdiction over your property.