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

Some Restrictions

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

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

Key Facts

Governing rule: ZDO Section 839
Number allowed: One per dwelling
Max size (urban): 900 sq ft; 500 in R-2.5
Rural minimum lot: Two acres, one dwelling
Rural STR use: Prohibited

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 Clackamas County, OR rules below cover local size, height, and setback requirements.

Summary

In unincorporated Clackamas County, ZDO Section 839 allows one ADU per single-family dwelling. Inside an urban growth boundary the ADU maxes at 900 sq ft (500 sq ft in R-2.5). Oregon HB 2001 mandates ADUs statewide. Cities set their own rules.

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

Only one accessory dwelling unit shall be allowed per detached single-family dwelling or manufactured dwelling. The maximum floor area of an accessory dwelling unit shall be: 500 square feet in the R-2.5 District; and 900 square feet in all other zoning districts.

View official code

Full Breakdown

Clackamas County's Zoning & Development Ordinance Section 839 governs ADUs in the unincorporated county. Inside an urban growth boundary or unincorporated community, only one ADU is allowed per detached single-family or manufactured dwelling, capped at 900 sq ft (500 sq ft in the R-2.5 district), and none in a cottage-cluster or manufactured-dwelling park. Outside a UGB (rural), an ADU needs a lot of record of at least two acres with one dwelling, a 900 sq ft cap, and must sit within 100 feet of the primary home; rural ADUs cannot be used as short-term rentals. Effective Sept. 3, 2024, ADUs were expanded to more rural-residential areas. Oregon's 2019 HB 2001 requires cities to permit ADUs.

Violations & Fines

Building or occupying an ADU without land-use and building permits is a zoning violation enforced by county Code Enforcement; unpermitted work can be ordered removed and fees assessed.

Frequently Asked Questions

How big can my ADU be?

Up to 900 square feet in most zoning districts (500 sq ft in the R-2.5 district). Rural ADUs outside an urban growth boundary are also capped at 900 sq ft.

Can I Airbnb my rural ADU?

No. ZDO 839.04(E) states use of an accessory dwelling unit outside a UGB as a short-term rental is prohibited.

Sources & Official References

Other rules in Clackamas County

Noise Ordinances: Construction HoursSome Restrictions Shed & Carport RulesSome Restrictions ADU Impact FeesSome Restrictions Noise Ordinances: Aircraft NoiseFew Restrictions Noise Ordinances: Leaf Blower RulesSome Restrictions Noise Ordinances: Vehicle NoiseSome Restrictions Noise Ordinances: Amplified Music & Outdoor SoundSome Restrictions Noise Ordinances: Decibel LimitsSome Restrictions

All Clackamas County rules

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

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