ADUs in Clark County, WA: Conversions, In-Law Suites & Detached Units

A detached accessory dwelling unit in the backyard of a Clark County home

An accessory dwelling unit is a second, smaller home on your property: a converted garage or basement, a suite attached to the house, or a standalone unit in the backyard. Homeowners build them for aging parents, adult kids, a private home office, or rental income, and Washington just made them far easier to add.

Under state law (HB 1337), most Clark County lots that allow a single-family home can now have up to two ADUs, with no requirement that you live on the property, and cities cannot cap an ADU below 1,000 square feet. That turns an ADU from a special-case project into one of the strongest moves a homeowner can make on their property's value and income.

We handle the whole thing as one accountable engagement: feasibility and zoning, design, permitting, and the build. And we think past the project. In the 360 Method an ADU is an Upgrade that should pay you back, so we help you weigh which type actually fits your lot, your budget, and the return you are after, then keep the home looked after once it is built.

What this typically costs

We publish our pricing instead of hiding it. Honest, realistic ranges for an average-size project; premium finishes and larger spaces go higher.

  • Garage or basement ADU conversion: $45,000 to $105,000+ - Convert existing space into a permitted living unit: framing, systems, kitchen, bath, and finish.
  • Attached ADU / mother-in-law suite: $80,000 to $155,000+ - A living suite attached to the home: addition, kitchen or kitchenette, bath, and a private entry.
  • Detached ADU: $140,000 to $270,000+ - A standalone unit on your lot, built ground-up: foundation, framing, full kitchen and bath, utilities.

Use the interactive estimator on this page to see a range for each option. The real number comes from a walkthrough and a written scope.

What's included

  • A feasibility and zoning check for your specific lot and goals
  • Design and layout matched to your budget, your lot, and how the unit will be used
  • Permitting handled through Clark County or the City of Vancouver
  • The full build: foundation or conversion, framing, kitchen, bath, and utilities
  • One point of contact from the first walkthrough to the final inspection

Signs it's time

  • Aging parents or adult children who need their own space close by
  • A goal of rental income or more long-term value from your property
  • A home office, studio, or guest space that the main house cannot give up
  • A large garage, basement, or backyard that is not pulling its weight

Common questions

Are ADUs allowed in Clark County and Vancouver?

Yes. Washington's HB 1337 requires cities and counties to allow ADUs on most lots that permit single-family homes, generally up to two per lot within urban growth areas. Rules vary by exact location, so the first step is a feasibility check for your specific address, which we handle.

Do I have to live on the property to have an ADU?

Not under the current Washington law. Owner-occupancy is no longer required for the main home or the ADU, which is what makes ADUs work as rental income, not just family housing.

Which type of ADU should I build?

It depends on your lot, budget, and goal. A garage or basement conversion is usually the most affordable because the shell already exists. An attached suite adds space to the house. A detached unit gives the most privacy and rental appeal but is a ground-up build. We help you compare all three on this page, then on a walkthrough.

What does an ADU cost?

Roughly: a conversion from about $45,000, an attached suite from about $80,000, and a detached unit from about $140,000, scaling with size and finish. Use the estimator on this page for a range on each, then we firm it up with a written scope.

Once your ADU is built, the Proactive Path keeps it and the main home maintained and documented on a schedule, so a rental-ready unit stays rental-ready. Explore the 360° Method membership.

Rules & resources

We build to code and to the rules where you live. ADU regulations are set by the state, the county, and your city, and they keep changing. These are the official sources; the first step on any ADU is confirming exactly what applies to your address, which we handle.

Related services

Serving all of Clark County, WA. Call (360) 838-6731 or schedule a consultation.