Does Benton County, WA have its own adu rules ordinance?

No. Benton County, WA does not appear to have a local adu rules ordinance, Washington state law applies instead. The rules summarized on this page come from Revised Code of Washington.

Key Facts Ordinance Text Full Breakdown Violations FAQ Sources More in Benton County

Benton County, WA Accessory Structures: ADU Rules (2026)

Few Restrictions

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

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

Key Facts

State Law: HB 1337 / RCW 36.70A.681
Where: Two ADUs, UGA lots
Minimum Size Cap: At least 1,000 sq ft
Owner-Occupancy: Cannot be required
Rural Lots: Follow county rural zoning

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 Washington under recent ADU streamlining laws. The Benton County, WA rules below cover local size, height, and setback requirements.

Summary

Washington's HB 1337 (RCW 36.70A.681) requires Benton County to allow at least two accessory dwelling units on single-family lots inside its urban growth areas, cannot cap ADUs below 1,000 square feet, and cannot require owner-occupancy.

City-specific rules exist: Kennewick has its own adu rules rules that differ from Benton County's county-level regulations. If you live in Kennewick, check the city-specific page instead.

The city or county must allow at least two accessory dwelling units on all lots that are located in all zoning districts within an urban growth area that allow for single-family homes.

Source: Revised Code of WashingtonView official code

Official source re-checked September 7, 2026: the cited page had not changed since it was quoted.

Full Breakdown

HB 1337 (2023), codified at RCW 36.70A.681, directs GMA-planning jurisdictions like Benton County to allow at least two accessory dwelling units on lots within an urban growth area that allow single-family homes: the county's UGAs are Kennewick, Richland, West Richland, Prosser, and Benton City. Inside those areas the county may not cap ADU size below 1,000 square feet, may not require owner-occupancy, and may not require off-street parking within half a mile of a major transit stop. Rural lots outside a UGA instead follow Benton County's rural zoning, which limits accessory dwellings more tightly. Any ADU still needs a building permit under the state building code.

Violations & Fines

Building or occupying an ADU without a Benton County building permit is enforced under RCW 19.27 with stop-work orders. County rules that conflict with RCW 36.70A.681 inside a UGA are unenforceable.

Frequently Asked Questions

Can I build an ADU in unincorporated Benton County?

On a lot inside an urban growth area that allows single-family homes, yes. HB 1337 requires at least two ADUs, up to at least 1,000 square feet each. Rural lots follow county zoning.

Do I have to live on the property?

No. Inside a UGA, RCW 36.70A.681 bars the county from requiring the owner to reside in or occupy the ADU or the main home.

Can my HOA block an ADU?

An HOA cannot entirely prohibit ADUs on lots where state law requires them to be allowed.

Sources & Official References

[1]Revised Code of Washington

Other rules in Benton County

Noise Ordinances: Quiet HoursSome Restrictions Shed & Carport RulesSome Restrictions Noise Ordinances: Decibel LimitsSome Restrictions Noise Ordinances: Amplified Music & Outdoor SoundSome Restrictions Noise Ordinances: Barking DogsSome Restrictions Parking Rules: EV ChargingFew Restrictions Fence Regulations: Material RestrictionsSome Restrictions

All Benton County rules

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

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ADU Rules in Cities Across Benton County

Kennewick, WA