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

Jefferson County adopted its comprehensive-plan and development-code update on July 13, 2026 (Ordinance 03-0713-26). Most changes took effect on adoption. Its official update page explains adoption and effective dates. Read the adopted amendments alongside the published code: a code page may still display text that an ordinance has replaced.

Start with your parcel’s zone and intended use, then check how the adopted rules apply before choosing a model.

Where ADUs are allowed

Eligibility depends on the land-use table. The adopted ADU section addresses existing single-family homes and accessory housing for existing industrial uses in LI and LI/C zones; industrial zoning is not a blanket prohibition.

Because eligibility is zone-specific, two nearby properties can land in different categories. The zoning on your exact parcel decides whether an ADU is allowed and under what conditions.

How many ADUs and how big

• Rural residential areas retain a one-ADU standard.
• The county’s update page identifies up to two ADUs per lot in the Irondale/Port Hadlock and Port Townsend UGAs. Eligibility in parts of Irondale/Port Hadlock also depends on proximity to sewer service.
• The size cap remains 1,250 square feet of gross floor area.

These provisions appear in Ordinance 03-0713-26, exhibit B-167. Utilities, critical areas, and the underlying zoning still need review.

Setbacks and height

Confirm setbacks and height against your zone, site conditions, and any applicable state urban ADU protections. Do not carry an urban exception into a rural site plan without checking its scope.

Water and septic

This is often a deciding factor in Jefferson County. To move forward, a property generally needs to show:

• Adequate potable water supply.
• Approved septic system capacity.

An unused bedroom allowance is not, by itself, approval for another dwelling. Have Environmental Health review the system records, condition, reserve area, and proposed use before treating an existing septic system as adequate.

Owner-occupancy and rental

The July amendment removes the owner-occupancy paragraph from JCC 18.20.020(2)(b). Older summaries that describe its removal as a future proposal are out of date.

The county regulates short-term rentals separately from this housing update. Confirm registration and use requirements directly with the county before including vacation-rental income in your plan.

Parking

Ask for the parking requirements that apply to the proposed site and use, including state protections for qualifying urban parcels. The number of usable spaces, driveway access, and delivery access should be resolved on the site plan before a proposal is finalized.

Permits and next steps

Before committing to a design in Jefferson County:

1. Confirm the zoning of your specific parcel and whether an ADU is allowed there.
2. Verify water supply and septic capacity for the actual proposed use.
3. Confirm which adopted code provisions apply to your application and whether the lot is within the UGA.
4. Check setbacks against your zoning and location.
5. Confirm parking expectations for your lot size and location.

The permit path itself generally moves through feasibility/zoning review, water and septic evaluation, site plan and building permit application, plan review, inspections, and final approval. Get these answered before you spend time on finish selections.

For delivery routes and how Jefferson County compares with the rest of the coast, see ADUs and beach cabins on the Washington coast.

Get a free Wolf property evaluation

Send us the property address and intended use. We will start with zoning, water and septic, current county rules, and model fit. Request your free Wolf property evaluation.

This is general information, not legal advice. Jefferson County adopted its current ADU rules on July 13, 2026 (Ordinance 03-0713-26), and other code updates are still in progress. Confirm current rules, fees, and application requirements with Jefferson County before you build.