Best DADU Builders in Seattle, Washington

Haas is the one company in Seattle that sits on both sides of the line, and that is worth more here than anywhere else in this silo. Haas Architectural appears on the City’s own pre-approved DADU gallery with a range of plans from a 288-square-foot studio up to a 940-square-foot two-storey. Haas Development & Construction holds the L&I registration to build. Most of the pre-approved designers cannot build, and most of the builders are not pre-approved designers.

Why that matters is scheduling, not prestige. Seattle’s own guidance says a pre-approved plan can get you a permit “as quickly as 2-6 weeks for most sites”, against the many months a custom design takes through SDCI. Going to one company for both halves removes the handoff where that saving usually leaks away.

The record supports it: registered since November 2016, $30,000 bond on an until-cancelled basis, and 5.0 across 28 Google reviews, which is the strongest rating-and-volume pairing in this market. Two dates to check before you sign, though. The registration expires December 10, 2026, and the liability policy on file expires August 30, 2026, which is about three weeks from now. Both are almost certainly routine renewals. Ask anyway.

Emerald City has the deepest review base in Seattle DADU work, 4.9 across 47 reviews, and the longest continuous L&I record on this page, registered since January 2011. Those two facts together are the strongest evidence base of anyone here, and it is not close.

They also cover the Eastside properly, which matters more than it sounds. Bellevue, Kirkland and Redmond each run their own permitting, and their ADU rules are not Seattle’s. A builder whose crews already cross the bridge regularly is worth more on an Eastside lot than a Seattle specialist who will be learning your jurisdiction on your money.

The trade-off is the permitting route. They are not in the City’s pre-approved DADU programme, so a Seattle build with them goes through full SDCI review rather than the two-to-six-week path a pre-approved plan can get you. If your priority is speed inside Seattle city limits, weigh that against the review record. If you are building in Bellevue or Redmond, the pre-approved programme is a Seattle thing and does not apply to you anyway.

Seattle ADU has the strongest registration record in this market and almost no reviews, and you should weigh both.

The record first. L&I registration SEATTA*811RQ has been active since December 2019 and runs to April 2028. The bond is $30,000 on an until-cancelled basis, which in Washington is what a healthy bond looks like, and they carry four separate liability policies on file ranging from $500,000 to $2,000,000. That is more insurance than anyone else on this page. They also publish a $220,000 to $600,000 range, and while that range is wide enough to drive a truck through, publishing anything at all is rare here.

Now the gap. Their Google profile carries a single review. One. A 5.0 built on one review tells you nothing at all, and I would rather say that plainly than let a perfect score sit on the page doing work it has not earned. Their 100+ DADU claim may well be accurate and their BBB rating is strong, but neither is the same as homeowners writing things down.

So: ask for five recent Seattle addresses and two homeowners you can phone. On a builder with this little public feedback, references are not a formality, they are the entire evidence base.

Ballard Backyard Cottages does one thing. Detached backyard cottages in Seattle, and not much else. In a market where most of your options are general contractors with a DADU page, a shop this specialized is worth a call, and they build from pre-approved designs by other designers as well as custom work.

The registration is clean: active since July 2019, $30,000 bond on an until-cancelled basis, $1,000,000 of liability insurance running to July 2027.

Two honest caveats. The reviews sit at 4.1 across 9, which is the weakest profile of the ranked builders here. Nine is a small sample and 4.1 is not bad, but it is the only builder on this page whose independent feedback is neither strong nor absent, and that middle ground deserves questions rather than a shrug.

The other is a name collision that nearly caught me. There is a separate L&I record for Ballard Backyard Company, a different entity with a different principal, which is expired and carries an L&I suspension date of January 14, 2020. That is not this company. If you look them up yourself, check the registration reads BALLABC817MJ and the principal is Michael Murray.

I have left Seattle Modern Buildings on this page with no best-for tag, and the reason is a gap I could not close.

Their L&I registration, SEATTMB746LD, shows an effective date of June 4, 2026. That is two months ago. Their marketing describes 600+ homes built and 70+ homes a year. Those two facts do not sit together comfortably. The most likely explanation is a re-registration under a new entity, which happens constantly and is usually benign, but L&I shows no earlier registration under this business name and I could not find the predecessor entity to confirm the continuity.

Everything else reads fine. The bond is $30,000 on an until-cancelled basis, liability insurance runs to June 2027, and Google shows 4.8 across 33 reviews, which is a real independent record and notably deeper than a two-month-old company would normally have. That in itself supports the re-registration theory rather than undermining it.

So this is a question, not an accusation. Ask them directly which entity built those 600 homes, whether it is still in good standing, and which entity will sign your contract. A clear answer resolves this entirely. No answer would tell you something too.