Cowlitz County, WA ADU (accessory dwelling unit) Rules (2026): City or County?
Cowlitz County ADU planning: Longview, Kelso, Castle Rock, Kalama, and Woodland each file separately from unincorporated county land. What to confirm before a Wolf build.
Cowlitz County sits on I-5 between Clark County and Lewis County, close to our Battle Ground factory. Being close doesn’t simplify the permit. Longview, Kelso, Castle Rock, Kalama, and Woodland each run their own building counter. Unincorporated Cowlitz County is another one. A Kelso mailing address on a county parcel still files with the county.
The statewide urban rules are summarized in the Washington ADU laws guide. Local size caps, owner-occupancy language, and floodplain along the rivers are what usually change the site plan. City FAQs can fall out of date, so we check the adopted code when we file.
What to confirm before you pick a model
- City limits versus unincorporated county, from the parcel, not the mailing address.
- Whether a detached second dwelling is allowed, and the size and height limits that apply today.
- Sewer versus septic, and whether the existing service can take another dwelling.
- Floodplain, industrial setbacks, and hillside access. River-adjacent lots and alley lots run into different problems.
- A truck path from the street to the pad. Longview’s grid streets and a steep county driveway need different delivery plans.
Local notes by city:
What Wolf does
We identify the reviewer, look at access and utilities, and tell you if a factory-built home is a fit before you spend money on a plan that the lot cannot hold. Production is in Battle Ground. Turn-key work in Washington covers the permit support, the site, the haul, and the set.
Request a free property evaluation.
General planning notes. Confirm current adopted requirements with Cowlitz County or the city that covers the parcel.
Sources
Requirements change, so check the current forms and rules with your jurisdiction before you file. This is general information, not legal advice.