Detached ADU (DADU) Permits in Woodinville

A standalone backyard cottage with its own foundation, roof, and exterior. Maximum flexibility on layout; highest construction cost. State law bars a city maximum below 1,000 sq ft of gross floor area, except on lots with critical areas (RCW 36.70A.681).

Free lookup: your lot’s zoning and setbacks, with a detached ADU placed on it to move and turn.

Permit fees in Woodinville

Set by the Woodinville fee schedule.

Woodinville fee schedule

Woodinville 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 a detached ADU

Every application (22)

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
Clearing and grading plan

The other 14

Drainage and erosion control plan
Tree plan
Foundation plan
Floor plan
Roof plan
Roof + floor framing plan
Typical building / wall section
Building elevations N/S/E/W
Glazing + door schedule (NFRC U-factor / SHGC)
Structural design notes (loads, materials, inspections)
Major materials schedule
Structural and lateral calculations
WSEC energy compliance, prescriptive path
Energy calculations

Where the lot or the work calls for it

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.