Everything homeowners ask about building an ADU in Woodinville — answered with 2026 data.
Yes, ADUs are allowed in Permitted (P) in the R-1, R-4, R-6, R-8, R-12 and R-18 residential zones (Woodinville Municipal Code Table 21.21.050, row "Dwelling Unit, Accessory"). Not listed — and therefore not allowed — in R-24, R-48 or in any commercial, industrial or other zone. Special development conditions are at WMC 21.41.020. Note the Woodinville quirk in WMC 21.21.030(3): all ADUs count in determining the type of residential land use, so a primary unit plus two attached ADUs is interpreted as a three-unit townhouse or stacked flat, which pulls in the Low-Rise Residential Design Standards in Chapter 21.38 WMC in Woodinville, WA. The maximum size for a detached ADU is 1,500 sq ft of habitable floor area, with a minimum of 300 sq ft (WMC 21.41.020(3)(b)) — 500 sq ft above the 1,000 sq ft floor RCW 36.70A.681(1)(f) guarantees. "Habitable floor area means the gross floor area of a building reduced by subtracting floor areas for vehicle parking, covered and uncovered outdoor open-air floors, and floor areas having less than five-foot-high ceilings," so a garage bay and a low attic do not count against you. The real limit on most lots is building coverage under Table 21.32.050(1), which in R-1 steps down as the lot gets bigger — from 40% on lots under 5,000 sq ft to 15% on lots of 43,560 sq ft and over, with bands at 35%, 28%, 22% and 20% in between — while minimum landscaping coverage climbs to as much as 75% on the largest R-1 lots. Check your own band with Woodinville Development Services at (425) 489-2700 before sizing the building. Attached ADUs can be up to Same 1,500 sq ft habitable floor area cap. 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 $250,000-$450,000. The cost per square foot averages $300-$500. Garage conversions are more affordable at $120,000-$250,000, while prefab ADUs cost $180,000-$350,000. Permit fees add Confirm current amounts with Woodinville Development Services at (425) 489-2700. Development fees are set by City Council resolution rather than in the code (WMC 21.13.040), the city publishes a 2026 Development Services fee schedule, and the Director may require an advance deposit for outside consultant review — which is common where a critical areas report has to be peer-reviewed (WMC 21.13.050 and 21.13.060). A disputed fee estimate is appealable to the Hearing Examiner (WMC 21.13.070) to your budget. See our detailed Woodinville ADU cost guide.
Detached ADUs in Woodinville can be up to 1,500 sq ft of habitable floor area, with a minimum of 300 sq ft. Attached ADUs are limited to Same 1,500 sq ft habitable floor area cap. 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 Not a category in Washington, and Woodinville has no junior ADU designation. An ADU carved out inside the house is simply an attached ADU and gets the same 300 to 1,500 sq ft range. Maximum height is 35 feet in R-1, R-4, R-6, R-8 and R-12; 45 feet in R-18 (WMC Table 21.32.040(2)) — an ADU takes the zone's standard, since WMC 21.41.020(3) subjects ADUs to the development standards of the underlying zone except as it modifies them, and it does not modify height. A pitched roof may go up to 10 feet above that limit where the space it creates is not designed for habitation and the slope does not exceed one foot of rise over two feet of run (WMC 21.32.040(6)(h)). Height is measured from average designated grade six feet out from the outer walls (WMC 21.32.040(5)(b)). You are allowed up to Two accessory dwelling units per parent lot on a qualifying lot.
Rear setback: Woodinville does not use a separate rear setback — Table 21.32.030(2) sets a single "minimum setback from interior property lines": 10 feet in R-1, and 5 feet in R-4, R-6, R-8, R-12, R-18, R-24 and R-48. Note 2 to the table cuts the R-1 figure to 5 feet on R-1 lots smaller than 15,000 sq ft. And WMC 21.41.020(3)(c) goes to zero: "A detached accessory dwelling unit may have the zoning setback reduced to zero from any property line abutting a dedicated public alley". Side setback: The same interior-property-line standard — 10 feet in R-1 (5 feet where the R-1 lot is under 15,000 sq ft), 5 feet in every other residential zone (WMC Table 21.32.030(2)). Roof eaves may protrude 18 inches into an interior setback and covered decks, patios and porches 18 inches (WMC 21.32.030(5)). Front setback: 10 feet from a street property line in every residential zone, but 20 feet for an attached or detached garage, measured along the driveway centreline from the vehicle door to the street property line (WMC Table 21.32.030(2)). If your ADU includes a garage bay, the 20-foot figure governs that part of the building. Note that garage conversions may be exempt from setback requirements if the existing structure is already within the setback area.
One stall per accessory dwelling unit (WMC Table 21.37.030, row "Accessory dwelling unit") — half what a three-bedroom house on a 6,000 sq ft lot must provide. Tandem parking is allowed for residential developments where assigned to individual dwelling units (WMC 21.37.060(6)). Woodinville's code contains no major-transit-stop parking exemption; if your site is within one-half mile walking distance of a major transit stop, RCW 36.70A.681(2)(a)(i) bars any off-street parking requirement at all — but that protection, like the rest of the statute, does not reach a lot designated with critical areas or their buffers. Confirm with Development Services at (425) 489-2700. 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 imposes no owner-occupancy condition, and RCW 36.70A.681(1)(b) separately bars a city from requiring "the owner of a lot on which there is an accessory dwelling unit to reside in or occupy the accessory dwelling unit or another housing unit on the same lot." This is one of the places where Woodinville's local code matters most: on a critical-area lot the state bar switches off under RCW 36.70A.681(4), and Woodinville still does not impose owner-occupancy. 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 Confirm with Woodinville Development Services at (425) 489-2700 — no published ADU review timeline was found in a city source, and the city's website could not be reached from this research session. Budget additional weeks if a critical areas report or a SEPA determination is required. Plan check: Standard building plan review under Chapter 21.62 WMC. Prefabricated units are allowed provided they sit on a permanent foundation (WMC 21.41.020(4)(c)). Conversions of existing enclosed structures, detached garages included, are allowed even where the structure does not comply with current building coverage or setback standards, provided the structure and the nonconformance were legally established (WMC 21.41.020(4)(a)). If the lot has a wetland, stream, geologically hazardous area, frequently flooded area or critical aquifer recharge area, expect a critical areas report under WMC 21.51.060, mitigation sequencing under WMC 21.51.050, and a minimum 10-foot building setback from the edge of any riparian management zone or wetland buffer under WMC 21.51.050(3). Pre-approved plans availability: No city pre-approved ADU plan library was found in a Woodinville source — unlike neighbouring Kirkland and Redmond. Confirm with Development Services at (425) 489-2700, and note that Washington State Department of Commerce maintains a statewide pre-approved plan effort you may be able to draw on.
Average ADU rental income in Woodinville: 1-bedroom units rent for $1,900-$2,400/month, 2-bedroom units for $2,400-$3,100/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), which points to the short-term rental definition in RCW 36.70A.696). Woodinville's ADU rules are built for long-term tenancy — which, given the school impact fee exemption and the halved park impact fee, is clearly the point. Expected ROI: 5-8% annual return.
The minimum lot size for an ADU in Woodinville is No ADU-specific minimum. The district minimum lot area governs: 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, 2,400 in R-18 (WMC Table 21.31.030). RCW 36.70A.681(1)(e) requires a city to allow an ADU on any lot meeting the minimum lot size for the principal unit, and Woodinville adds none 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 $120,000-$250,000. 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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