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

In Clallam County, ADU eligibility depends on your zoning designation and parcel size, so start by checking whether your specific parcel qualifies.

The rural figures below come from the county’s published code. Inside an Urban Growth Area, review Washington’s urban ADU protections first: RCW 36.70A.680 addresses when state requirements take effect and override conflicting local rules. The rural size and owner-occupancy restrictions below should not be treated as a countywide answer.

Two types of ADU

Clallam County recognizes two kinds of accessory dwelling unit:

• Attached ADU — shares a common wall, floor, or ceiling with the primary dwelling.
• Detached ADU — a separate structure or outbuilding.

A detached ADU connected to the primary dwelling only by a covered breezeway is still treated as detached. In all cases, the ADU must be incidental and subordinate to the primary residential use.

Where ADUs are allowed

ADUs are allowed in many situations, but not every parcel qualifies. A few thresholds matter early:

• The property must be a legally created parcel.
• Outside urban growth areas, a detached ADU generally requires a parcel of at least 1.5 acres.
• That 1.5-acre requirement may be waived when the parcel has a community water supply and adequate sewage disposal.
• Detached ADUs are prohibited in Commercial Forest zones.
• Agricultural Retention zones carry additional restrictions.

Published rural size limits

For detached ADUs, the published rule limits gross floor area to the smaller of 50% of the primary dwelling or 1,250 square feet. Units of 400 square feet or less are exempt from that size rule.

For attached ADUs, the unit may not exceed 35% of the gross floor area of the primary dwelling.

The county lists a September 29, 2026 hearing for proposed comprehensive-plan and zoning amendments. Check its ordinance notices before applying; a pending hearing does not establish adoption.

Water, septic, and sewer

Utilities are often the deciding factor in Clallam County:

• The ADU must use the same potable water source as the associated primary residential dwelling.
• An ADU is not permitted unless the Environmental Health Division certifies that the water supply and sewage disposal are adequate.
• Acceptable water sources include an existing individual well or a community water system.
• Acceptable sewage disposal includes an existing individual septic system, a community system, or municipal sewer.
• Permitting may require proof of potable water, a current septic system, or proof of sewer connection.
• Parcels in the Dungeness Water Rule area may require mitigation for well use.
• Sites near water bodies or other critical areas may carry special conditions.

Owner-occupancy and rentals

The published rural standards tie the ADU to the owner living on the property:

• The owner of the parcel must live in either the primary dwelling or the ADU as their primary residence.
• Either the primary dwelling or the ADU may be used as a vacation rental, but not both.
• A Notice to Title must be recorded with the Clallam County Auditor. This document runs with the land.

Parking and access

• The primary dwelling and the ADU must share a single access point from the road. No new access may be established for the ADU.
• On-site parking must be provided.

For an urban parcel, have the county apply the relevant state parking protections and exceptions rather than copying a rural parking assumption.

Permits and next steps

An ADU requires a building permit approved before any new construction or modification, and an ADU worksheet must accompany the building permit application. Depending on the project, you may also need a detailed scaled site plan, structural drawings, structural calculations, Washington State energy calculations, and proof of ownership.

The ADU worksheet captures the property information, tax parcel number, acreage, zoning, site plan confirmation, primary dwelling floor area, ADU type and floor area, structure type, water source, sewage disposal method, and ingress/egress details.

Ask for the applicable urban or rural requirements in writing when comparing models and preparing a site plan.

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

Start with your parcel

For a Clallam County project, the early questions are whether your parcel meets the acreage and zoning thresholds, whether it can support the ADU’s water and septic needs, and whether a smaller footprint avoids a constraint a larger model would trigger.

Send us the property address and intended use, and we will start with zoning, parcel size, utilities, and model fit. Request a free Wolf property evaluation.

This is general information, not legal advice. Clallam County’s ADU rules are evolving under Washington law. Confirm current code, fees, and application requirements with Clallam County before you build.