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Kennewick, WA Accessory Structures: ADU Rules (2026)

Some Restrictions

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

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

Key Facts

ADUs per lot: Two, any configuration
Max floor area: 1,100 sq ft each
Detached height cap: 24 feet
Parking required: 1 space per ADU
Impact fees: 50% of primary dwelling's

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 Kennewick, WA rules below cover local size, height, and setback requirements.

Summary

Kennewick allows two accessory dwelling units per lot in every residential zone, each capped at 1,100 square feet and 24 feet in height if detached, under KMC 18.12.020: a local rule that already tracks Washington's 2023 HB 1337 statewide floor.

Two accessory dwelling units shall be permitted in all residential zoning districts in the following configurations: (a) One attached accessory dwelling unit and one detached accessory dwelling unit; (b) Two attached accessory dwelling units; or (c) Two detached accessory dwelling units... The maximum height for an ADU that is detached from the primary unit shall be 24 feet... The total gross floor area of an ADU shall not exceed 1,100 square feet.

View official code

Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Code of Ordinances: Supplement 19 Update 2).

Full Breakdown

KMC 18.12.020 permits two ADUs per lot in any residential zoning district, in any combination of one attached and one detached, two attached, or two detached units (which may be one or two structures). There's no separate minimum lot size beyond the zone's base minimum. A detached ADU is capped at 24 feet in height; an attached ADU follows the primary structure's zone height limit. Total gross floor area can't exceed 1,100 square feet, one off-street parking space is required per ADU, and converting an attached garage to an ADU requires replacing the lost parking elsewhere on site. ADUs are assessed 50 percent of the primary dwelling's impact fees. Washington's 2023 HB 1337 independently requires GMA cities to permit two ADUs per lot in most urban residential zones and bars many former restrictions like owner-occupancy and minimum lot size: state law now sets the floor, and Kennewick's ordinance (last amended by Ord. 6037 in 2023) reflects it.

Violations & Fines

Building an ADU over 1,100 square feet, over the height cap, or without the required off-street parking space is a zoning violation subject to Planning Division code enforcement and permit denial.

Frequently Asked Questions

Can I build two ADUs on one Kennewick lot?

Yes. KMC 18.12.020 permits two ADUs per lot in any residential zone, as one attached and one detached, two attached, or two detached units.

Is there an owner-occupancy requirement for Kennewick ADUs?

No such requirement appears in KMC 18.12.020; Washington's 2023 HB 1337 barred local owner-occupancy mandates statewide.

Sources & Official References

[1]Kennewick Municipal Code § 18.12.020 — Accessory Dwelling Units (ADUs)

Other rules in Kennewick

Parking Rules: Street Parking LimitsSome Restrictions Shed & Carport RulesSome Restrictions Parking Rules: Commercial & Oversized VehiclesSome Restrictions Fence Regulations: Material RestrictionsSome Restrictions Animal Ordinances: Exotic PetsHeavy Restrictions Animal Ordinances: Pet LimitsSome Restrictions Landscaping Rules: Tree TrimmingSome Restrictions

All Kennewick rules

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

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