Attached ADUs & Mother-in-Law Suites in Clark County, WA
An attached ADU, often called a mother-in-law suite, adds private living space to your home: typically an addition or a reworked wing with its own kitchen or kitchenette, a full bath, and a separate entrance. It keeps family close while giving everyone their own front door.
It is the middle path between converting existing space and building a detached unit. You get more square footage than a conversion and more independence than a spare bedroom, tied into the home's structure and systems.
Because it adds real, livable square footage, an attached suite is also a strong move on your home's value and flexibility. We scope it to fit how your family actually lives now and how the space can serve you later, whether that is aging parents today and rental or resale value down the road.
What this typically costs
An average attached adu / mother-in-law suite in Clark County runs roughly $80,000 to $155,000+, 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: $160-$200 per square foot. A clean, functional attached suite with an efficient kitchen and full bath.
- Better: $200-$250 per square foot. Upgraded finishes, better windows and lighting, a more open layout.
- Best: $250-$310 per square foot. High finish, custom cabinetry, and quality fixtures throughout.
- Premium: $310-$380 per square foot. Premium, design-led suite with custom details and top-tier finishes.
Estimate any size: total = the per square foot rate above times the square footage, with a project minimum of $55,000 to $70,000. Try the interactive estimator.
What's included
- Design that ties the suite into your home's structure, roofline, and systems
- A private entrance, plus a kitchen or kitchenette and a full bathroom
- Heating, electrical, and insulation built for year-round comfort
- Permitting through Clark County or the City of Vancouver
- One accountable team from design through final inspection
Signs it's time
- Aging parents who want independence but need to be close
- Adult children who need their own space without leaving home
- A desire for more usable square footage tied into the main house
- Flexibility for family now and rental or resale value later
Common questions
What is the difference between a mother-in-law suite and a detached ADU?
A mother-in-law suite is attached to your home, sharing a wall and the home's structure, while a detached ADU is a standalone building. Attached suites are usually less expensive than detached units and keep family under one roofline; detached units offer the most privacy and rental appeal.
Does a mother-in-law suite need its own kitchen?
To count as an ADU it generally needs its own kitchen or kitchenette and bathroom. We can build a full kitchen or a compact kitchenette depending on how the space will be used and the rules for your lot.
Once the suite is built, the Proactive Path keeps it and the main home maintained and documented on a schedule. 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.