Detached ADUs in Clark County, WA
A detached ADU is a standalone home on your lot, built from the ground up with its own foundation, walls, roof, kitchen, bath, and utilities. It is the most private and the most rentable type of ADU, and the one that adds the most independent value to a property.
It is also a real construction project, and we treat it like one. We design and build the unit as one accountable engagement: site work and foundation, framing and roof, full mechanical, kitchen and bath, and the exterior that ties it to your home and neighborhood. You have a single point of contact from feasibility to final inspection.
Of the ADU options this is the biggest investment, so the return matters most. We help you size and spec it to the income or use you are after, then keep it maintained once it is built, because a detached unit you can rent for years is an asset, not just a project.
What this typically costs
An average detached adu in Clark County runs roughly $140,000 to $270,000+, depending on size and finish. A complete planning range with nothing hidden to add later. Final materials, any structural work, and site conditions are set on a walkthrough, so a detailed estimate can land higher. The real number comes from that walkthrough.
- Good: $240-$300 per square foot. A complete standalone unit with an efficient kitchen, full bath, and durable finishes.
- Better: $300-$370 per square foot. Upgraded finishes, better windows and roofline, a more open plan.
- Best: $370-$450 per square foot. High finish throughout, custom cabinetry, quality fixtures, designed exterior.
- Premium: $450-$560 per square foot. Premium, architect-detailed unit with top-tier finishes inside and out.
Estimate any size: total = the per square foot rate above times the square footage, with a project minimum of $90,000 to $110,000. Try the interactive estimator.
What's included
- Feasibility, site planning, and zoning for a standalone unit on your lot
- Foundation, framing, roofing, and a weather-tight exterior built for the PNW
- A full kitchen and bathroom, heating, electrical, and independent utilities
- Permitting through Clark County or the City of Vancouver
- One accountable team managing the whole ground-up build
Signs it's time
- You want the most private, most rentable type of ADU
- Rental income or long-term property value is the main goal
- You have backyard space and want a true second home on the lot
- Family who needs a fully independent, standalone living unit
Common questions
How much does a detached ADU cost in Clark County?
A detached, ground-up ADU typically runs from about $140,000 and scales with size and finish, because you are building a complete small home including foundation and utilities. Use the estimator on this page for a range, then we firm it up with a written scope.
How big can a detached ADU be?
Washington law prevents cities from capping an ADU below 1,000 square feet, and Vancouver caps an ADU at 1,000 square feet. Most detached units land between about 500 and 800 square feet. We size yours to your lot, budget, and goal.
A detached unit you rent for years is an asset. The Proactive Path keeps it and the main home maintained and documented so it stays one. 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.
- Washington State: ADU law (RCW 36.70A.681, from HB 1337)
- Washington State Dept. of Commerce: Accessory Dwelling Units
- Clark County (unincorporated): ADUs and Cottage Housing
- City of Vancouver: Accessory Dwelling Units
- City of Camas
- City of Washougal
- City of Ridgefield
- City of Battle Ground
Related services
Serving all of Clark County, WA. Call (360) 838-6731 or schedule a consultation.