ADU (accessory dwelling unit) Planning in Wahkiakum County, WA (2026)

For an ADU in Wahkiakum County, establish the permitting jurisdiction and whether another permanent dwelling is allowed on the property before choosing a home. Confirm county requirements for unincorporated land and the applicable town requirements for property inside Cathlamet. A mailing address alone does not establish the boundary.

Confirm the dwelling approval

The county’s official permit page provides building applications, setback information, road standards, and shoreline resources. It is not a countywide ADU eligibility determination.

Ask Building and Planning to confirm the permitted dwelling use, number of units, allowable size and placement, and any land-use approval needed for your parcel. Do not assume a conditional-use permit is always required, or that a particular square-footage allowance follows from Washington’s urban ADU legislation.

Water and wastewater approval

The county’s published instructions say permanent residences need approved potable water and sewer or septic before applying for a building permit. Obtain the well or water-service records and the approved septic design early.

Ask Environmental Health whether the proposed dwelling can be served, whether the bedroom count changes the approved septic capacity, and whether additional design or utility work is needed. Show the existing and proposed systems, including septic replacement areas, on the site plan.

Setbacks, shoreline, and floodplain

Use the county’s current setback information and have staff confirm its application to the proposed foundation, porches, decks, and other structures. Identify shoreline, floodplain, drainage, and critical-area constraints before fixing the home’s location.

A raised foundation can affect stairs, ramps, decks, and access to doors. Include these in the usable building area and project budget, rather than assuming the home footprint alone is enough.

Access and intended use

Confirm driveway and road-approach requirements, emergency access, and any required parking. The county publishes private-road and road-approach resources. Ask staff how many parking spaces your ADU needs rather than assuming a fixed count.

Explain whether the home is for family, a long-term tenant, or short-term guests. Obtain the applicable use and rental requirements before relying on income. A recreational structure or a building approved without residential facilities is not approval for a permanent home.

Modular construction and your next step

Wolf’s factory construction still leaves local foundation, placement, utility, and inspection approvals to resolve. We also check the delivery route, staging area, and trailer or crane setting needs.

Send the address or parcel number and intended use. Keep surveys, water/septic approvals, and any earlier permit conditions available so we can start with the property’s actual constraints and compare suitable Wolf models.

Request a free Wolf property evaluation.

General planning information. Confirm current adopted requirements and fees with the responsible permitting office before committing to a design.