What does an ADU or DADU permit cost in Seattle?
Updated November 11, 2026 · Built from official fee schedules and city permit records
How Seattle figures the fee
Seattle prices building permits from the project's value. SDCI turns the value into a development fee index using Table D-1 of the 2026 Fee Subtitle (for example, $325 for the first $1,000, then $1.60 per extra $100 up to $25,000). You pay that amount once as the permit fee and once more as the plan review fee. Projects that qualify as subject to field inspection (smaller work reviewed in the field instead of in full plan review) pay only 40% of the index for plan review. Fees went up about 18% on January 1, 2026.
Example fees at typical ADU / backyard cottage values
| Project value | Development fee index | Permit + plan review fee |
|---|---|---|
| $93,145 | $1,726.30 | $3,453 |
| $150,000 | $2,209.00 | $4,418 |
| $230,846 | $2,836.75 | $5,674 |
| $300,000 | $3,359.00 | $6,718 |
How long it takes
Across 509 ADU / backyard cottage permits Seattle issued in the last 12 months, the median wait was 183 days. A quarter took 107 days or less, and a quarter took 294 days or more.
The project value declared on these permits had a median of $230,846; the middle half ran from $176,266 to $453,358. Many fees are figured from this number, so it is the best guide to what a similar project will pay.
Good to know
- SDCI's own 2026 example: a 500 sq ft detached ADU valued at $93,145 pays $3,453 in plan review and permit fees.
- Converting a house into ADUs and building a new main house counts as one of the larger projects in this group.
More Seattle permit guides
- Building permit cost in Seattle
- How long permits take in Seattle
- New house permit cost
- Remodel and addition permit cost
- Deck permit cost
Sources
- Fees: SDCI 2026 Fee Subtitle (Table D-1 and D-2)
- Permit data: Seattle Building Permits (data.seattle.gov), permits issued November 1, 2025 to October 31, 2026. Processing time is measured from application date to issue date.
This is an independent guide built from public records. It is not affiliated with the Seattle Department of Construction and Inspections (SDCI). Fees change, and the city calculates your final fee when you apply; confirm the amount with the city before you budget.
Common questions
How much is a ADU / backyard cottage permit in Seattle?
At the median project value of $230,846, the 2026 SDCI permit and plan review fees come to about $5,674. The fee rises with project value.
How long does a ADU / backyard cottage permit take in Seattle?
The median ADU / backyard cottage permit issued in the last 12 months took 183 days from application to issue.
Did Seattle permit fees go up in 2026?
Yes. SDCI raised construction permit fees about 18% on January 1, 2026, and most other fees 6.5%.