Methodology

Sources

Permit data comes from the City of Seattle SDCI Building Permits open dataset. We include permits whose description references an accessory dwelling unit (ADU, DADU, AADU) or that use Seattle's pre-approved DADU plan program — 12,473 permits as of 2026-08-30. License data comes from the Washington L&I Contractor License registry, refreshed with each site build.

How rankings work

Builders are ranked by completed ADU permits attributed to them in city records, with total permits as the tiebreaker. We merge obvious name variants of the same company and match businesses to state licenses by exact legal name.

What this misses — read this

Seattle stopped publishing contractor names on most permit records after 2021, so recent projects are under-attributed: 800 of 12,473 tracked permits name a contractor. A builder's absence here, or a low count, is not evidence they haven't built ADUs — it means city open data doesn't attribute those permits. We are enriching recent records and expanding city coverage; builders can claim their profile to submit permit numbers we can verify against city records.

License statuses

"Active", "expired", and "suspended" chips reproduce the state registry verbatim as of the build date. Licenses change; a mismatch can also mean a company operates under a different legal name. Always re-verify at lni.wa.gov/verify before hiring.

Independence

Rankings cannot be bought. Paid placements, when offered, are labeled as such and never alter permit counts or rank order.