An accessory dwelling unit (ADU) — also called a backyard cottage, DADU, or in-law suite — is one of the most valuable additions a Kitsap County homeowner can make, and good design is what separates a cramped box from a comfortable, light-filled second home. Designing an ADU in Poulsbo, Bainbridge Island, Bremerton, or Port Orchard means balancing three things at once: how the space lives day to day, how it fits your lot, and how it satisfies Kitsap County zoning and Washington’s ADU law. This guide walks through ADU types, the county’s current rules, the design and permitting process step by step, what drives the investment, and how to get started — written from the perspective of a local architecture and interior design studio that handles projects from concept through permit-ready drawings.
An accessory dwelling unit is a second, self-contained residence — with its own kitchen, bathroom, and living space — on a lot that already has a primary home. In Kitsap County, ADUs take two basic forms, and the choice shapes the entire design:
The right choice depends on your goals, your lot, and how the unit will be used. A well-designed ADU can serve as a parents’ suite, a returning-graduate apartment, a home office or studio, a guest house, or a long-term rental — and because it may fill several of those roles over a home’s lifetime, flexibility built in from the start is one of the most valuable things thoughtful design provides.
Smart ADU design starts with the regulations, because they define the envelope you get to design within. Kitsap County’s rules differ depending on whether your lot sits inside or outside an Urban Growth Area (UGA):
| Standard | Inside a UGA | Outside a UGA (rural) |
|---|---|---|
| Number of ADUs allowed | Up to 2 per lot (attached, detached, or a mix) | Typically 1 |
| Maximum size | Smaller of 1,000 sq ft or 60% of the primary home’s habitable area | Smaller of 900 sq ft or 50% of the primary unit |
| Siting | Must meet the zone’s setbacks, height, and lot coverage | Detached ADU within 150 ft of the main home (or convert an existing structure such as a garage) |
These local standards sit on top of a major statewide change. Under Washington House Bill 1337 (codified as RCW 36.70A.696), effective July 2024, fully planning cities and counties must allow at least two ADUs per lot within urban growth areas. The law also prohibits jurisdictions from imposing owner-occupancy requirements, from requiring ADU floor area below 1,000 square feet, from setting height limits below 24 feet, and from applying setback, aesthetic, or design-review standards more restrictive than those for the principal home. In practice, this gives Kitsap homeowners far more design freedom than they had a few years ago — but the exact rules for your parcel depend on your zone and location, so confirming them up front is always the first design step.
To make ADUs faster and easier to permit, Kitsap County and the Kitsap County Department of Community Development launched a pre-approved ADU plans program with the cities of Bremerton, Bainbridge Island, Port Orchard, and Poulsbo. These are architect-designed, code-reviewed plans you can use to skip much of the custom-design and plan-review timeline.
An important nuance: the pre-approved plans are free to use in the urban areas of Kitsap County and anywhere within Bremerton, Bainbridge Island, Port Orchard, or Poulsbo, as long as you make no modifications. They are not free in the rural areas of unincorporated Kitsap County. Pre-approved plans are an excellent option for straightforward, flat lots with standard conditions. However, many Kitsap properties — hillside lots, waterfront parcels, unusual shapes, or homes with a specific design vision — benefit from a custom design that responds to site conditions, views, solar orientation, and the aesthetic relationship between the ADU and the main home. We can help you determine whether a pre-approved plan or a custom design is the right fit for your property and goals.
Designing an ADU follows the same phased path as any residential project — the same full-spectrum design services we bring to every home, scaled to a smaller footprint. Here’s what each phase involves:
Every good ADU starts with a close look at your lot — slope, trees, drainage, utilities, solar orientation, views — and a conversation about how the unit will be used and who will live in it. This is also where zoning, setbacks, and critical-area constraints are confirmed before a single wall is drawn.
The architect translates your goals into preliminary floor plans, massing studies, and where the unit sits on the lot. Several layout options are usually explored so you can react to real arrangements rather than abstractions.
The chosen concept is refined: exact dimensions, window and door placement, finishes, and the structural and mechanical systems. This is also where interior design decisions — cabinetry, storage, fixtures, and materials — come together into a cohesive palette, the same attention to detail you’ll see throughout our interior design work.
Detailed, dimensioned drawings and specifications are produced for permitting and construction. In Kitsap County, this is the set submitted to the Department of Community Development for plan review.
We help navigate the county’s plan-review process, responding to comments and corrections so the permit moves forward as smoothly as possible.
During construction, the designer can stay engaged — answering builder questions, reviewing substitutions, and confirming the work matches the drawings. This is where our established relationships with trusted local fabricators and contractors keep the project moving and the craftsmanship high.
Within the regulatory envelope, the difference between a cramped unit and one that feels like a real home comes down to design. These principles guide our ADU work:
ADUs are one of the fastest-growing segments of American residential construction. ADU construction in the U.S. has increased by roughly 55% over the last five years, according to National Association of Home Builders industry research, and about 42% of that demand is driven by multigenerational living — families choosing to keep aging parents or adult children close while preserving everyone’s independence. With the 2025 U.S. remodeling market estimated at more than half a trillion dollars and nearly half of homeowners planning a project, adding well-designed living space is one of the most popular ways homeowners invest in their property today.
Cost is one of the first questions homeowners ask, and the honest answer is that an ADU’s total investment depends heavily on choices you control and conditions you don’t. Rather than a single number, it helps to think about cost as a set of contributing factors — understanding what moves the budget up or down puts you in a far better position to plan. The main cost drivers for an ADU include:
Because these factors interact, two ADUs of the same size on different lots can carry very different budgets. The most reliable way to understand your numbers is to start with a clear program and site assessment, then gather written estimates from a licensed local contractor. We’re glad to help frame the cost conversation realistically before you commit to a direction.
An ADU is a small building with all the complexity of a large one — structure, systems, zoning, and livability packed into a tight footprint. An architect coordinates all of it into one permit-ready package, advocates for your vision through plan review, and solves the hard design problems (fitting a second dwelling onto an existing lot, capturing light and views, making a small space feel generous) that determine whether the finished unit is merely legal or genuinely livable. If you’re weighing whether you need an architect, our companion guide on how to hire an architect in Kitsap County walks through what to look for.
Inside an Urban Growth Area, an ADU can be up to the smaller of 1,000 square feet or 60% of the primary home’s habitable area. Outside a UGA (rural), the limit is generally the smaller of 900 square feet or 50% of the primary unit. Your specific zone and lot determine the exact figure, so confirm it with Kitsap County before design begins.
If your lot is inside an Urban Growth Area, Washington’s HB 1337 and Kitsap County code allow up to two ADUs per lot — any combination of attached and detached. Outside a UGA you’re typically limited to one. Designing for two units is its own challenge, balancing privacy, parking, and the overall look of the property.
They’re free to use in the urban areas of Kitsap County and anywhere in Bremerton, Bainbridge Island, Port Orchard, or Poulsbo, provided you make no modifications. They are not free in the rural areas of unincorporated Kitsap County. Pre-approved plans speed up permitting on standard lots, but custom design is often the better fit for hillside, waterfront, or distinctive properties.
Design typically runs a few months for an ADU, with county plan review added on top. Decision speed on your end — approving layouts and selecting finishes — has a real effect on the timeline, so starting early, especially before a busy building season, is always the right call.
Daylight, ceiling height, and smart storage are the three biggest levers. Large windows and a well-placed skylight, ceilings raised where the roof allows, open sightlines from kitchen to living area, and built-in cabinetry that keeps the floor clear all make a compact unit feel open and livable rather than tight.
A great ADU is small in footprint but big in thoughtfulness. At Bluefoot Architecture & Design, we help homeowners across Poulsbo, Bainbridge Island, Bremerton, and Port Orchard design accessory dwelling units that work beautifully within Kitsap County’s zoning and Washington’s ADU law — from siting and daylight to cabinetry, finishes, and contractor coordination. We handle your project from concept through permit documents and construction, with established relationships with trusted local fabricators and contractors. Ready to explore what’s possible on your property? Contact our Poulsbo studio or call 360-602-2965 to start the conversation.
