Key takeaways
- There are three delivery routes: design-build, architect-led, and contractor-first. They differ in who carries design risk, not just in price.
- Design-build is one contract and one contract, one party responsible. Architect-led gives you competitive bids and independent oversight of the builder.
- A detached DADU of 600 to 800 sq ft runs roughly $280,000 to $450,000 all-in on the Eastside. Garage conversions start near $80,000.
- Percentage-priced architects run 8% to 15% of construction cost whichever route you choose; Piper Cole quotes a fixed fee. In design-build that fee is inside the builder’s number, not absent from it.
- Kirkland ADU permit review runs 5 to 9 weeks, Bellevue 6 to 10, Seattle 8 to 14. The route you pick does not change the city’s clock.
Searches like ADU builder Kirkland and ADU design build Kirkland are asking one practical question: who is actually going to deliver this thing, and who do I call first. Most pages answer with zoning rules. This one answers the question.
I should be straight about my own position before you read further. Piper Cole Architects is an architecture firm. I design ADUs and I administer construction. I am not a general contractor and I do not build. That shapes what I recommend below, so weigh it accordingly, and I have tried to describe the route that does not involve me as fairly as the ones that do.
The three ways an ADU gets delivered
Design-build
One firm holds both the design and the construction contract. You sign once. The designer and the builder are the same business, so coordination is internal and nobody can blame the other party for a conflict in the drawings.
The trade-off is that you lose the check. The party producing the drawings is the party pricing the work, so there is no independent set of eyes asking whether the price is fair or the detail is right. You are trusting one firm’s judgement on both. For a straightforward DADU from a reputable firm that is often a reasonable trade.
Architect-led
You hire the architect first. The design is developed and permitted, then that drawing set goes out to two or three general contractors who bid the same scope. You hold two contracts. The architect then runs construction administration, which means visiting the site, answering the builder’s questions, reviewing changes and confirming what is built matches what was approved.
The advantage is leverage. Competitive bids on an identical scope tell you what the work is worth, and the person checking the builder’s work is not paid by the builder. The trade-off is two contracts, a longer runway before you break ground, and you sit between two parties if they disagree.
Contractor-first
You go to a builder, and they bring in a designer or a drafter to produce a permit set. It is often the cheapest route on paper, and common on small garage conversions.
It works when the project is genuinely simple. It goes wrong when the lot is not: a critical area, a steep slope, a tight setback or an awkward utility run needs design thinking before pricing, and a permit set drawn to satisfy the city is not the same as a design resolved to build from.
The three routes compared
| What matters | Design-build | Architect-led | Contractor-first |
|---|---|---|---|
| Contracts you sign | One | Two | One, sometimes two |
| Who carries design risk | The design-build firm | The architect | Effectively you |
| Competitive pricing | No, single source | Yes, two or three bids on one scope | No, single source |
| Independent site oversight | No | Yes | No |
| Time before construction | Shortest | Longest | Short |
| Best suited to | Straightforward lots, speed | Complex lots, cost control, design-led outcome | Simple garage conversions |
What each route costs
The construction number barely moves between routes. What moves is how the fee is presented to you.
On the Eastside in 2026, a detached DADU of 600 to 800 sq ft runs roughly $280,000 to $450,000 all-in. A simple garage conversion starts near $80,000. A premium detached unit on a complex lot reaches $650,000 and above. The full breakdown by type, with the soft costs most people forget, is in the Eastside ADU cost guide.
Percentage-priced architectural work runs 8% to 15% of construction cost. That is true in every route. In design-build it is inside the single number you are quoted rather than a separate invoice, which sometimes gets read as design-build being cheaper. It is not cheaper by default, it is bundled. If you want to compare routes like for like, ask a design-build firm what portion of the price is design and engineering, and compare that with an architect’s fee proposal. Our fee structure guide sets out how those numbers are built.
How to choose for your lot
Lean design-build when the lot is rectangular and flat, the ADU is close to a standard size, speed matters more than a bespoke result, and you have a firm you already trust.
Lean architect-led when any of the following is true: the lot has a critical area, a slope or an unusual shape; you want competitive bids because the budget is tight; the design matters to you beyond meeting code; or you will not be on site regularly during construction and want somebody independent watching.
Lean contractor-first only for a simple conversion inside an existing footprint, where the structure is sound and nothing about the site is unusual.
The honest summary: the more unusual your lot, the more the independent design and oversight earns its fee. On a plain lot with a plain box, it earns less.
Kirkland, Redmond, Sammamish and Bellevue
The delivery route does not change the city’s review clock, and the clock is worth planning around.
Kirkland reviews an ADU permit in roughly 5 to 9 weeks, faster than Seattle. Lot coverage and a lower height limit than Seattle’s are the usual constraints. See Kirkland ADU rules and our Kirkland practice.
Bellevue runs 6 to 10 weeks and permits two ADUs per lot, which changed the maths for a lot of owners. See Bellevue ADU rules.
Redmond allows up to two ADUs per lot and offers expedited review. Our Redmond page covers the local pattern.
Sammamish permits up to two, with critical areas the most common complication. See Sammamish.
Seattle proper runs 8 to 14 weeks by the standard path, and it also has a faster pre-approved plan route with its own trade-off. Both are covered in the Seattle section below.
Building an ADU in Seattle proper
Most of this page is written for the Eastside, but I hear the same question from Seattle owners, usually phrased as who is the right ADU builder or contractor in Seattle. The three delivery routes work the same way inside the city. What changes is the permit path, and Seattle gives you a second option that is worth understanding before you choose a builder.
The standard path. A custom ADU design goes through full plan review, which runs 8 to 14 weeks in Seattle. That is longer than Kirkland or Bellevue, so build the clock into your plan from the start. The stage-by-stage breakdown is in the Seattle ADU permit timeline.
The pre-approved plan route. Seattle offers pre-approved DADU plan sets. Build from one and the permit can come through in 1 to 3 weeks. The design itself has already been reviewed, so permitting focuses on site-specific compliance: setbacks, lot coverage and utility connections. The trade-off is simple. You build an existing design rather than one drawn for your lot and your household.
My view: the pre-approved route is often the right call when speed matters and a standard design sits comfortably on the lot. A custom design earns its extra weeks when the lot is unusual, when a standard footprint fights the setbacks or the slope, or when the design itself matters to you. Check what your lot allows in Seattle DADU rules before you commit either way.
How it fits the delivery routes. A pre-approved plan is a drawing set, not a builder. You still need somebody to build it, and the design-build, architect-led and contractor-first logic above applies unchanged. What shrinks is the design work on the unit itself. What does not go away is the site: where the unit sits, the utility and sewer runs, drainage and the foundation all still need design attention, and site work is where ADU budgets break in Seattle as much as anywhere. The questions in the next section apply to a Seattle builder word for word.
My role in Seattle is the same as on the Eastside. I work with both custom designs and pre-approved sets, and if you are weighing a pre-approved plan against a custom design for your lot, that is a conversation I am glad to have. I do not build either one.
Questions to ask any ADU builder before you sign
These are ADU-specific. The broader vetting process, references, licensing, insurance and bid comparison, is set out in how to choose a general contractor on the Eastside.
- How many detached ADUs have you completed in this specific city in the last two years? Permit familiarity is local, not regional.
- Who produces the structural engineering, and is it inside your price?
- What is your allowance for site work, utilities and the sewer connection? This is where ADU budgets break.
- Show me a change order from a recent ADU. How were extras priced and approved?
- Who answers a city correction notice, and is that time billable?
- If this is design-build, what portion of the contract is design and engineering?
- Can I speak to an owner whose ADU you finished more than a year ago? Year-one problems are the informative ones.
Where we fit, and where we do not
We design the ADU, take it through permitting, help you put the drawing set out to bid, and administer construction once a builder is appointed. On request we will review a design-build proposal you have already received and tell you whether the scope and the price line up, which is a small piece of work that occasionally saves a very large mistake.
We do not build. If what you want is a single firm to design and build, an ADU design-build company is the right call and I would rather say so than pretend otherwise. If you want the design resolved properly and somebody independent watching the build, that is our work. More detail on the design side is on our ADU design service page, and the broader comparison lives in design-build versus architect.
Questions
Is Piper Cole Architects an ADU builder or general contractor?
No. We are an architecture firm. We design ADUs, take them through permitting and administer construction, and we do not hold the construction contract or self-perform any building work. If you want a single firm to both design and build, a design-build company is the right fit and we will say so.
What does design-build mean for an ADU?
One firm holds both the design and the construction contract, so you sign once and coordination between designer and builder is internal. The trade-off is that the party drawing the work is also the party pricing it, so there is no independent check on scope, price or quality.
Do I still need an architect if I hire a design-build firm?
Not as a second designer. Some owners do hire an architect for a limited review of a design-build proposal, to confirm the scope and price line up before signing. Architectural and engineering work happens either way: in design-build it sits inside the single quoted number rather than on a separate invoice.
How long does an ADU permit take in Kirkland?
Kirkland ADU permit review runs roughly 5 to 9 weeks, which is faster than Seattle’s 8 to 14 weeks on the standard path. Bellevue runs 6 to 10 weeks. The delivery route you choose does not change the city’s review clock.
Who builds ADUs in Seattle, and is the pre-approved plan route faster?
The same three routes apply in Seattle: design-build, architect-led or contractor-first, chosen the same way as on the Eastside. On timing, Seattle’s standard ADU permit path runs 8 to 14 weeks. Building from one of Seattle’s pre-approved DADU plan sets can shorten the permit to 1 to 3 weeks, because review focuses on site-specific compliance such as setbacks, lot coverage and utility connections. The trade-off is that you build an existing design rather than a custom one, and a pre-approved plan still needs a builder and still needs its site work designed properly.
What does an ADU cost on the Eastside in 2026?
A detached DADU of 600 to 800 sq ft runs roughly $280,000 to $450,000 all-in. A simple garage conversion starts near $80,000, and a premium detached unit on a complex lot reaches $650,000 and above. Percentage-priced architectural work runs 8% to 15% of construction cost in any delivery route; Piper Cole quotes a fixed fee.
Can I act as my own general contractor on an ADU?
You can, and on a simple garage conversion some owners do. It means you carry scheduling, subcontractor coordination, liability and the cost of any sequencing mistake. On a detached unit with its own foundation, utilities and sewer connection, the coordination load is heavier than most owners expect.
Authoritative sources
Regulatory requirements referenced in this guide are set by the official agencies below. Rules change, always confirm current requirements with the source:
