Everything homeowners ask about building an ADU in Woodinville — answered with 2026 data.
Yes, ADUs are allowed in Permitted outright (P) in R-1, R-4, R-6, R-8, R-12 and R-18 (WMC Table 21.21.050, row "Dwelling Unit, Accessory", note 1 pointing to WMC 21.41.020). Not listed in R-24, R-48 or any commercial, industrial or other zone, so not allowed there (WMC 21.21.030(2)(g)). Under WMC 21.21.030(3) ADUs count when classifying the residential use: a house plus two attached ADUs reads as a three-unit townhouse or stacked flat, which in R-1 to R-8 brings in the Chapter 21.38 Low-Rise Residential Design Standards in Woodinville, WA. The maximum size for a detached ADU is 300 to 1,500 sq ft of habitable floor area (WMC 21.41.020(3)(b)), 500 sq ft above the 1,000 sq ft floor in RCW 36.70A.681(1)(f). Habitable floor area is gross floor area minus vehicle parking, covered and open-air floors and space under 5-ft ceilings, so a garage bay or low attic does not count. Building coverage (Table 21.32.050(1)) is the practical cap: R-1 steps from 40% on lots under 5,000 sq ft to 15% at 43,560 sq ft and over; R-4 35%; R-6 50%; R-8 55%; R-12 and R-18 60-65%. Attached ADUs can be up to Same 300 to 1,500 sq ft of habitable floor area. An ADU "may be fully contained inside a primary dwelling unit, attached or stacked to a primary or accessory dwelling unit, attached or stacked on a building containing an accessory residential use, or may be standalone one-unit dwellings". Woodinville has an ADU-friendliness score of 8/10. Check our full Woodinville ADU rules page for complete zoning details.
ADU construction in Woodinville typically costs $325,000-$550,000. The cost per square foot averages $400-$650. Garage conversions are more affordable at $100,000-$225,000, while prefab ADUs cost $300,000-$450,000. Permit fees add 2026 schedule (Resolution 668): permit fee on valuation ($148.28/sq ft for wood-frame R-3, WMC 21.62.060), plan review 65% of it, fire plan review 13.2% of that, $6.50 state surcharge. A 1,000 sq ft detached ADU comes to about $3,480, plus $119 plus $25 per fixture for mechanical and plumbing to your budget. See our detailed Woodinville ADU cost guide.
Detached ADUs in Woodinville can be up to 300 to 1,500 sq ft of habitable floor area. Attached ADUs are limited to Same 300 to 1,500 sq ft of habitable floor area. An ADU "may be fully contained inside a primary dwelling unit, attached or stacked to a primary or accessory dwelling unit, attached or stacked on a building containing an accessory residential use, or may be standalone one-unit dwellings". Junior ADUs (JADUs) have a cap of Washington has no junior ADU category and Woodinville's code has none. A unit carved out inside the house is simply an attached ADU (WMC 21.11B.050) with the same 300 to 1,500 sq ft habitable floor area range. Maximum height is 35 ft in R-1, R-4, R-6, R-8 and R-12; 45 ft in R-18 (WMC Table 21.32.040(2), re-read 20 Sept 2026). WMC 21.41.020(3) applies the zone's standards to an ADU and does not modify height. A pitched roof (hip, gable or shed; not mansard or gambrel) may rise up to 10 ft above the limit if the space is not habitable or opens onto 7-ft walls below and the pitch is 1:2 or flatter (WMC 21.32.040(6)(h)). Height is measured from average finished grade 6 ft out from the walls (WMC 21.32.040(5)). You are allowed up to Two ADUs per parent lot on a qualifying lot.
Rear setback: No separate rear setback: Table 21.32.030(2) sets one "minimum setback from interior property lines", 10 ft in R-1 (5 ft on R-1 lots under 15,000 sq ft, note 2) and 5 ft in R-4, R-6, R-8, R-12 and R-18. A detached ADU "may have the zoning setback reduced to zero from any property line abutting a dedicated public alley" (WMC 21.41.020(3)(c)). Add a 10-ft building setback from the edge of any wetland or riparian buffer (WMC 21.51.050(3)). Side setback: Same interior-line standard: 10 ft in R-1 (5 ft where the R-1 lot is under 15,000 sq ft), 5 ft in every other residential zone (WMC Table 21.32.030(2)). Roof eaves may project 18 in. into an interior setback, chimneys and bay windows 24 in., covered porches 18 in. (WMC 21.32.030(5)). Front setback: 10 ft from a street property line in every residential zone; 20 ft for an attached or detached garage, measured along the driveway centreline from the vehicle door to the street line (WMC Table 21.32.030(2), note 1). If the ADU includes a garage bay, the 20-ft figure governs that part. Eaves may project 24 in. and covered porches 5 ft into a street setback (WMC 21.32.030(5)). Note that garage conversions may be exempt from setback requirements if the existing structure is already within the setback area.
One stall per ADU (WMC Table 21.37.060, row "Accessory dwelling unit", Ord. 792 § 22, 2025); tandem stalls assigned to a unit are fine (WMC 21.37.070(6)). Washington's 2025 parking law (SB 5184, RCW 35A.21.445) exempts code cities of 30,000 or fewer people (subsection (6)(a)), so it does not reach Woodinville. RCW 36.70A.681(2)(a)(i) still bars any ADU parking requirement within one-half mile walking distance of a major transit stop, except on lots with critical areas or buffers (subsection (4)). Many cities and states have been relaxing ADU parking requirements in recent years. In California, no additional parking is required for ADUs near transit.
Not required. WMC 21.41.020 has no owner-occupancy condition, and RCW 36.70A.681(1)(b) bars a city from requiring the owner to live in the ADU or the main house. On a critical-area lot the state bar switches off (RCW 36.70A.681(4)) but Woodinville's code still imposes nothing. RCW 36.70A.681(1)(k) requires the city to allow an ADU to be sold as a condominium unit (again, not on critical-area lots); WMC 21.41.020 is silent on it, so ask Development Services about the process. Note that owner-occupancy rules vary by state law — California and several other states have eliminated this requirement for standard ADUs.
The ADU permit review timeline in Woodinville is typically WMC 21.80.210 (Ord. 782, 2025): the city must say whether the application is complete within 28 days and decide a construction permit within 120 days of the completeness date; the clock pauses while it waits for your corrections. Plan review covers two resubmittals; a critical areas report adds time. Plan check: Standard building plan review under Chapter 21.62 WMC. Prefabricated units are allowed on a permanent foundation (WMC 21.41.020(4)(c)). Conversions of existing enclosed structures, detached garages included, are allowed even where the structure breaks current coverage or setback rules, provided it and the nonconformance were legally established (WMC 21.41.020(4)(a)). The Director may approve deviations from zoning standards for accessibility features (WMC 21.41.020(3)(e)). If the lot has a wetland, stream, steep slope, flood area or critical aquifer recharge area, expect a critical areas report (WMC 21.51.060), mitigation sequencing (WMC 21.51.050) and the 10-ft building setback from any riparian zone or wetland buffer (WMC 21.51.050(3)). Structural review sent to an outside consultant is billed at cost, with an advance deposit if it is expected to exceed $5,000 (2026 fee schedule, note 4). Pre-approved plans availability: None. Woodinville publishes no pre-approved ADU plan set: the city's Permitting and Applications & Forms pages (archived 6 Jan 2026) list none, and the code contains no expedited ADU track, unlike Kirkland's four registered plans. Confirm with the Permit Center at 425-489-2754 whether plans approved elsewhere would shorten review.
Average ADU rental income in Woodinville: 1-bedroom units rent for $2,400-$2,700/month, 2-bedroom units for $2,800-$3,150/month. Short-term rentals: No. "Accessory dwelling units are prohibited from being rented for periods of fewer than 30 consecutive nights" (WMC 21.41.020(5), re-read 20 Sept 2026, pointing to the short-term rental definition in RCW 36.70A.696). Expected ROI: 5-9% gross annual yield on a $325,000-$550,000 detached build renting at $2,400-$3,150/mo, before vacancy, taxes, impact fees and financing; a garage conversion at $100,000-$225,000 yields roughly double.
The minimum lot size for an ADU in Woodinville is No ADU-specific minimum. The zone minimums are 35,000 sq ft in R-1, 9,000 in R-4, 6,000 in R-6, 5,000 in R-8, 3,600 in R-12 and 2,400 in R-18 (WMC Table 21.31.030, Ord. 792 § 16, 2025). RCW 36.70A.681(1)(e) requires the city to allow an ADU on any lot that meets the minimum lot size for the principal unit, and Woodinville adds nothing of its own. This applies to detached ADUs — garage conversions and JADUs may have different or no lot size requirements.
Garage conversions are one of the most popular and affordable ADU options. In Woodinville, a garage conversion typically costs $100,000-$225,000. The key advantages are lower cost (no foundation work), potential setback exemptions, and faster permitting. Read our complete garage conversion guide.
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