Attached ADU (AADU) Permits in Woodinville
An ADU built inside or attached to the primary residence — basement conversion, garage conversion, or bump-out addition. Lower cost; constrained by the primary footprint.
Free lookup: your lot’s zoning and setbacks, with an attached ADU placed on it to move and turn.
Permit fees in Woodinville
Set by the Woodinville fee schedule.
Woodinville fee scheduleWoodinville values a new ADU, attached or detached, by its floor area at the rates in Table 21.62.060, $165.67 a sq ft for wood frame (Group R-3, type VB), and an ADU made from existing space on the applicant's estimate (WMC 21.62.060(1)-(2)); the building permit comes off the City's 2026 fee table, plus plan review at 65% of that fee and the $6.50 state surcharge. Plumbing and mechanical work on the Combined Building Permit adds $25 a fixture. Electrical permits come from L&I, at L&I's fees. Park, transportation and school impact fees, where they apply, are set in WMC 3.36, 3.39 and 3.38, and any water or sewer connection charge by the serving utility (Woodinville Water District for most lots), not by the City. Apply through Woodinville's online Permit Portal (aca-prod.accela.com/woodinville/default.aspx); the Apply for a Permit Online page (woodinville.gov/347/Apply-for-a-Permit-Online) explains the account setup.
Review timeline
Not published by Woodinville.
What Woodinville asks for with an attached ADU
Every application (10)
- Building/Mechanical/Plumbing Permit application, online Permit Portal
- Owner Authorization Form
- Project narrative
- Water Availability Certificate, and Sewer Availability Certificate or septic approval
- Site address
- King County parcel number
- Site plan
- Floor plan
- WSEC energy compliance, prescriptive path
- Energy calculations
Where the lot or the work calls for it
Where the ADU adds onto the house or changes its structure
- Clearing and grading plan
- Drainage and erosion control plan
- Tree plan
- Foundation plan
- Roof plan
- Roof + floor framing plan
- Structural design notes (loads, materials, inspections)
- Structural and lateral calculations
Where the ADU adds onto the house or changes its outside walls, windows or roof
- Typical building / wall section
- Building elevations N/S/E/W
- Major materials schedule
Where the work changes the outside walls, windows or roof
- Glazing + door schedule (NFRC U-factor / SHGC)
Only if the King County Surface Water Design Manual's drainage review for the work calls for a Technical Information Report
- Drainage study (Technical Information Report)
Where the lot has a critical area
- Critical area study and mitigation plan
Where the lot has a steep slope, is in a landslide hazard area, is in an erosion hazard area, is in a seismic hazard area or has ground that needs a soils study
- Geotechnical report
In the case each one names
- Electronic set of all plans (project valued over $250,000)
From the city’s own documents: City of Woodinville Development Services — Building/Mechanical/Plumbing Permit application (revised June 2026), last read November 7, 2026. An address’s own page checks its lot for slopes, flood zones and critical areas.
AADU-specific requirements
- Egress on every bedroom — IRC R310 net clear opening ≥5.7 sf; sill ≤44″ from floor.
- Smoke + CO alarms — interconnected throughout primary + AADU per IRC R314/R315.
- 1-hr separation — required between AADU and primary in some cases; otherwise a continuous draft stop.
- Independent kitchen + bath — full plumbing + cooking provision in the AADU.
- Address or unit number — the city or county assigns addresses; ask the permit center whether the unit gets its own.