ADU (accessory dwelling unit) Rules and Regulations in Yakima County, WA (2026)

For a Yakima County ADU, establish whether the property is inside a city or in unincorporated county jurisdiction. Then identify its zone and whether it lies inside an urban growth area. A Yakima mailing address alone does not select the correct code.

Confirm the housing category

The county regulates ADUs under YCC 19.18.020, with permitted locations determined by the land-use table in Chapter 19.14. An ADU is different from a caretaker dwelling, an accessory kitchen, or a non-habitable accessory structure. Approval for one of those uses does not establish permission for an independent rental home.

The published ADU section describes a secondary dwelling associated with a detached single-family home. It excludes parcels containing a duplex, multifamily dwelling, or commercial/industrial use from that ADU provision. Check the actual use table and current rules for the parcel before assuming a detached cottage is allowed.

Size, placement, and access

The published county section requires the ADU to be smaller in floor area than the main house, applies the primary structure’s setbacks, and generally requires a shared driveway unless the homes may access different roads. Its accessory-housing provisions include a one-unit limit and refer parking to Chapter 19.22.

For an urban-growth-area project, ask Planning how current state ADU requirements affect those published provisions. Do not automatically carry rural or older county restrictions into an urban project. Confirm allowable unit count, floor area, height, setbacks, parking, and any rental conditions before selecting a model.

Water availability is a separate approval

The Yakima Health District specifically says that sharing a well with a new residence or ADU requires proof of a valid water right as part of building approval. A working well or an unused plumbing connection is not proof of that right.

The county ADU standards require both homes to connect to a qualifying public water system and meet health requirements. A shared-well proposal therefore needs review of the system’s classification, legal supply, and connection approval. The Health District does not grant water rights; resolve legal availability early.

Sewer and septic

The published county ADU section requires public sewer for both homes within an urban growth area. Outside the urban growth area it refers to the applicable two-connection requirements, and all sewage systems must meet health standards.

Have the reviewer identify the rule applicable to your property. For an onsite system, obtain the approved design, bedroom capacity, inspection information, and replacement-area requirements. For sewer, request the provider’s connection scope and fees.

Permit documents and model fit

The county’s forms page provides an ADU application packet, a required water-availability supplement, and a standard application checklist. Use those current resources to confirm the submission requirements and fees.

Wolf also checks the delivery route, driveway, staging area, foundation location, and setting equipment. Factory construction still needs local site and utility approvals. A smaller home can reduce some site demands, but it cannot resolve an unavailable legal water supply or a prohibited use.

Send the address or parcel number, intended use, and available water/septic records. Request a free Wolf property evaluation and compare the current models.

General planning information. Confirm current adopted requirements with the county or city and the relevant health and utility authorities before committing to a design.