ADU Architects Near Me: How to Choose One on Bainbridge Island, Kitsap, and Seattle

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ADU
If you’re searching for ADU architects near you in West Puget Sound, filter on three things. Pick someone who has permitted ADUs in your jurisdiction, who has a portfolio of small buildings that actually got built, and who will tell you honestly whether you need custom design at all. That last point matters more than it used to. Since late 2025, homeowners on Bainbridge Island and across Kitsap County can use free, pre-approved ADU plans. For a simple backyard cottage on a flat lot, that may be enough. Hire an architect when your site, budget, or goals don’t fit a stock plan. Coates Design is a residential architecture studio on Bainbridge Island, led by Matthew Coates, AIA. We design ADUs, guest houses, and backyard cottages on the island, across Kitsap, and in Seattle. This guide covers what changed in the rules, what ADUs cost here, and how to vet any ADU architect, including us.

What an ADU Architect Does (and When You Don’t Need One)

An ADU architect’s main job is to make the unit fit your lot before anyone draws a floor plan. On the west side of the Sound, that means checking zoning, setbacks, critical areas, shoreline designations, septic or sewer capacity, and well or water service first. After that, a full-service ADU architect typically handles:
  • Feasibility and site planning, including where the unit can go and how big it can be
  • Schematic design options sized to your budget
  • A complete permit set: architectural drawings, structural coordination, and energy code compliance
  • Permit submittal and responses to reviewer comments
  • Bid review and construction administration, so the built unit matches the drawings
There are four common ways to get an ADU designed. Each fits a different situation.
Route Design cost Best fit Watch out for
Kitsap pre-approved plan Plan set is free; permit fees still apply Flat, simple lots where one of six layouts works Site review still applies: zoning, critical areas, utilities
Prefab or modular unit Bundled into the unit price Speed and a predictable box price Foundation, utilities, crane access, and permits are often extra
Drafter or designer Usually lower fee Straightforward garage or basement conversions Not a licensed architect; slopes, shorelines, and structure get harder
Licensed architect Fee scales with scope Custom fit, tricky sites, higher-end finishes, guest houses Costs more up front; ask what’s included
If a pre-approved plan fits your lot and you like it, use it. A good architect will say so in the first meeting.

2026 ADU Rules in Washington, Bainbridge Island, and Kitsap

State law now sets a floor for ADUs, and Bainbridge loosened its own code in October 2025. Here’s what matters for your design.

Washington State (HB 1337)

The 2023 law applies to cities and counties that fully plan under the Growth Management Act, which includes Kitsap and King. Within urban growth areas, local rules must now:
  • Allow two ADUs on lots that allow a single-family home, in any mix of attached and detached (WA Senate bill report)
  • Drop owner-occupancy requirements
  • Cap ADU impact fees at 50% of what the main house would pay
  • Allow ADUs of at least 1,000 sq ft and at least 24 feet tall (Sightline)
Cities had until six months after their comprehensive plan update to comply; for many Puget Sound cities that was June 30, 2025 (WA Commerce). Local short-term rental rules can still apply.

Bainbridge Island

On Oct. 14, 2025, the city council unanimously passed an ordinance that (Bainbridge Island Review):
  • Raised the ADU size cap from 900 to 1,000 sq ft
  • Removed the shared-driveway requirement
  • Lets one-story ADUs sit closer to the road and main house, with planning department approval
  • Dropped the rule that ADUs keep the property looking like a single-family home from the street

Kitsap Pre-Approved ADU Plans

The Kitsap Regional Coordinating Council commissioned six permit-ready ADU plans that anyone can use for free in participating jurisdictions, including Bainbridge Island, Bremerton, Port Orchard, and Poulsbo (City of Bainbridge Island).
Plan Size Bedrooms Stories
The Lille 480 sq ft 1 1
The Sidney 600 sq ft 1 1
The Kitsap 672 or 834 sq ft 1 or 2 2
The Sinclair 800 sq ft 2 1
The Blakely 800 sq ft 2 2
The Salish 1,000 sq ft 3 1
Source: City of Bainbridge Island pre-approved ADU plan sheet These plans skip design fees and some building reviews. They do not skip site review: zoning, critical areas, shoreline designations, and utility capacity still apply, and permit fees are still due. The city recommends talking to Planning and Community Development about your site before choosing a plan.

A Tax Break Worth Knowing

Washington offers a three-year property tax exemption on qualifying improvements, including building an ADU, if the work costs no more than 30% of the home’s prior assessed value. Apply before construction is finished (WA Commerce).

What an ADU Costs Around Puget Sound

A detached ADU in the Seattle area commonly runs $300,000 to $450,000 or more, and conversions cost less because the shell already exists. These are contractor ranges from completed Seattle-area projects (New Image):
ADU type Typical project cost
Detached ADU (backyard cottage) $300,000 to $450,000+
Attached ADU or garage conversion $200,000 to $350,000
Basement conversion $100,000 to $250,000
On Bainbridge Island and in rural Kitsap, a few site factors can move those numbers in either direction:
  • Septic and wells. A lot on septic may need a system upgrade or a new drainfield to serve a second unit.
  • Critical areas and shorelines. Slopes, wetlands, and shoreline buffers shape where the ADU can sit and can add studies to the permit.
  • Utility runs. A long trench to reach power, water, or sewer adds up fast on large lots.
  • Access and logistics. Narrow drives, trees, and island delivery can add to site work and crane costs.
Timeline. Plan on several months of design and permitting before construction starts. Seattle-area builders report permitting alone at 3 to 5 months, shorter with a pre-approved plan (New Image). Ask your jurisdiction for current review times, since they change with workload.

How to Vet ADU Architects Near You

“Near me” matters for an ADU more than for most projects. Your architect needs to walk the site, know the local reviewers, and show up during construction. Use this checklist when you compare firms:
  1. Local permit history. Ask which ADUs they’ve permitted in your jurisdiction: Bainbridge Island, Kitsap County, Poulsbo, or Seattle. Each has its own reviewers and quirks.
  2. Built small buildings. Look for finished ADUs, cottages, or guest houses, not just large homes or renderings. Small footprints leave no room for wasted space.
  3. A license you can check. Confirm the architect’s license with the Washington State Department of Licensing.
  4. Site before floor plan. A good first meeting starts with your lot: setbacks, critical areas, septic or sewer, and utilities.
  5. Honesty about stock plans. If a free pre-approved plan fits your site, they should say so.
  6. A clear scope and fee. Know whether permitting support, consultant coordination, and construction administration are included.
  7. Energy and comfort. Ask how they approach heat pumps, ventilation, and the envelope. A small building gains and loses heat fast.
  8. Real proximity. Check that they can get to your site easily for visits and inspections, ferry schedule included.

Questions to Ask in Your First Meeting

Bring these to any ADU architect consultation. The answers show quickly whether a firm knows small projects and your local code.
  • Based on my lot, how large can the ADU be, and where can it go?
  • Would a pre-approved plan work here? Why or why not?
  • What site issues do you see: septic, slopes, trees, shoreline, utilities?
  • Which ADUs have you permitted in this jurisdiction, and how long did review take?
  • What’s included in your fee, and what would cost extra?
  • Who handles structural engineering and energy code compliance?
  • Will you stay involved during construction?
  • What would you change to bring my budget down without hurting how the unit lives?

Working with Coates Design on Your ADU

Our studio is on Bainbridge Island, so island and Kitsap sites are close to home. We also work across Seattle. Our residential work ranges from custom homes to guest houses, and a 500 sq ft cottage gets the same care as a full house. Small buildings reward careful planning: every window, closet, and step has to earn its place. Every ADU project follows the same path:
  1. Site and code review. We check zoning, critical areas, septic or sewer, and utilities before design starts, and tell you if a pre-approved plan makes more sense.
  2. Design options. Two or three schematic layouts sized to your lot and budget.
  3. Permit set. Architectural drawings coordinated with structural and energy code work, then submittal and reviewer responses.
  4. Construction. Bid review, site visits, and follow-through so the finished unit matches the design.
Planning in Seattle instead? See our Seattle ADU architect guide for city-specific rules. Building on the island? Our Bainbridge Island ADU guide goes deeper on local design ideas. Browse more of our residential work.

ADU Architect FAQ

Do I need an architect to build an ADU in Kitsap County?

Not always. If one of the six free pre-approved plans fits your lot, you can permit it without paying for custom design. You’ll want an architect for sloped or shoreline sites, septic constraints, a custom layout, or a guest house that has to match the main home.

How much does an ADU architect cost?

Fees depend on scope. A full design, permit, and construction package costs more than a floor plan alone. Most firms quote a fixed fee or a percentage of construction cost, so ask what’s included before comparing numbers.

Can I build two ADUs on my lot in Washington?

In most cities and urban growth areas, yes. HB 1337 requires fully planning jurisdictions to allow two ADUs on lots zoned for a single-family home, attached or detached. Lot size, setbacks, septic, and critical areas can still limit what fits.

What is the maximum ADU size on Bainbridge Island?

1,000 sq ft. The city raised the cap from 900 sq ft in October 2025.

Are Kitsap’s pre-approved ADU plans really free?

The plan sets are free. You still pay permit, review, and inspection fees, and your site still goes through zoning and critical-area review.

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

Under HB 1337, fully planning cities and counties can’t require owner occupancy for ADUs. Short-term rental rules are separate, so check local limits before planning an Airbnb.

How long does it take to design and permit an ADU?

Plan on several months before construction. Seattle-area permitting alone often takes 3 to 5 months, with pre-approved plans moving faster.

Talk to an ADU Architect on Bainbridge Island

Not sure whether your lot needs custom design or a pre-approved plan will do? Send us your address and what you want the ADU for. We’ll tell you what we see on the site and what a sensible next step looks like. Schedule a consultation with Coates Design