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Josephine County, OR Accessory Structures: ADU Rules (2026)

Some Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified September 2026

ADU rules in Josephine County, OR, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

Minimum lot size: 2 acres
Maximum ADU size: 900 square feet
Max distance from main home: 100 feet
ADUs allowed per lot: 1
Review type: Ministerial, Chapter 19.22 JCC

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Oregon under recent ADU streamlining laws. The Josephine County, OR rules below cover local size, height, and setback requirements.

Summary

In rural Josephine County's Rural Residential zones (RR-1, RR-2.5, RR-5), a homeowner may build one accessory dwelling unit under § 19.61.020(B) of the Rural Land Development Code, but only on a lot of at least two acres, capped at 900 square feet, and sited within 100 feet of the existing single-family home; only one ADU is allowed per lot.

These county ordinances apply to unincorporated areas of Josephine County. Incorporated cities within the county may have their own rules that take precedence over county-level regulations.

B. Accessory dwelling unit (ADU) as defined in JCC § 19.11.030, subject to the following standards: 1. The lot or parcel for the ADU is at least two acres in size and not located within an urban reserve as mapped in the County's GIS system; ... ... 4. The ADU is limited to 900 square feet in floor area and shall be located no more than 100 feet from the existing single-family dwelling; ... ... 9. Only one ADU is allowed on any lot or parcel.

View official code

Full Breakdown

020(B) permits an accessory dwelling unit in the Rural Residential zone as a ministerially reviewed use, but attaches ten conditions. 600; the ADU must meet sanitation and wastewater rules; and it is capped at 900 square feet and must sit within 100 feet of the primary dwelling. 495 requires. 76 JCC, Wildfire and Emergency Safety Standards: a vegetation-mitigation plot plan, compliance with building safety requirement R-327 and applicable state specialty codes, a driveway meeting evacuation-access standards, and proof of an approved domestic water supply from the Oregon Department of Water Resources.

Only one ADU is allowed per lot, and the county will not approve a subdivision, partition, or other division that would put the ADU on a separate lot from the primary dwelling. 020(D) lets a historic home be converted into an ADU instead, under its own size and rebuild limits.

Violations & Fines

Constructing an ADU that exceeds 900 square feet, sits more than 100 feet from the primary dwelling, or is built on a lot under two acres does not qualify for ministerial approval under § 19.61.020(B); Planning can deny or revoke the development permit issued under Chapter 19.41 JCC, and an ADU built without meeting these standards is an unpermitted structure subject to code enforcement.

Frequently Asked Questions

How big can a Josephine County ADU be?

§ 19.61.020(B)(4) caps a Rural Residential zone ADU at 900 square feet of floor area and requires it to sit within 100 feet of the existing single-family dwelling on the same lot, so a detached ADU cannot be sited elsewhere on a larger rural parcel.

What size lot do I need for an ADU?

§ 19.61.020(B)(1) requires at least two acres, and the lot cannot be mapped within an urban reserve area on the county's GIS system; a smaller Rural Residential lot does not qualify for an ADU under this section.

Can I build more than one ADU on my property?

No. § 19.61.020(B)(9) allows only one accessory dwelling unit per lot or parcel, and subsection (B)(10) blocks the county from approving a partition that would put the ADU on a separate lot from the primary dwelling.

Sources & Official References

[1]Josephine County Code § 19.61.020

Other rules in Josephine County

Animal Ordinances: Chickens & LivestockSome Restrictions Fence Regulations: Height LimitsSome Restrictions Shed & Carport RulesSome Restrictions Tiny HomesSignificant Restrictions ADU Rental RestrictionsSignificant Restrictions Parking Rules: Abandoned VehiclesSome Restrictions Fence Regulations: Material RestrictionsSome Restrictions Fence Regulations: Retaining WallsSome Restrictions Animal Ordinances: Veterinary Clinic ZoningLight Restrictions

All Josephine County rules

How Josephine County compares: Easiest Cities to Build an ADU·Compare Josephine County to another location·View the Oregon accessory structures overview

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