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Woodinville ADU and detached ADU rules

Woodinville ADU and DADU rules under the current code

Woodinville's 2025 ADU update is more flexible than many older summaries: it allows two ADUs and up to 1,500 square feet of habitable area. The detached building still has to fit the base zone, building coverage, landscaping, trees, critical areas, access, and utility conditions.

Reviewed August 14, 2026 against adopted city code and official city guidance

Quick definitions. An accessory dwelling unit (ADU) is a complete additional home on the same property. A detached ADU (DADU) is in its own building. FAR or GFA limits how much enclosed floor area the property may contain.

Bottom line

What the current rules mean

Up to two ADUs may be allowed on a parent lot. An ADU can be internal, attached, stacked, or standalone and may contain 300 to 1,500 square feet of habitable area. A legal existing structure can be converted even when it does not meet current setback or building-coverage standards, but a new DADU must pass the current site rules.

Up to 2ADUs per parent lotThe second ADU receives a specific unit-count treatment.
300–1,500Habitable square feetParking and open-air floor areas are excluded by definition.
No STRUnder 30 nightsThe code prohibits short-term ADU rentals.

What is allowed on one lot

Where the use table allows ADUs, a parent lot may have up to two. ADUs are generally included in the maximum dwelling units per lot, but the second ADU is excluded from that determination when the owner elects to build two that comply with WMC 21.41.020.

  • Fully contained inside a principal dwelling.
  • Attached or stacked with a principal dwelling or another ADU.
  • Attached or stacked on a building containing an accessory residential use, such as above a garage.
  • One or more standalone one-unit dwellings, subject to the two-ADU cap.

Official sources: WMC 21.41.020: accessory dwelling units · RCW 36.70A.681: limits on local ADU regulation

Size, height, setbacks, and site capacity

Maximum size
Each ADU must have at least 300 and no more than 1,500 square feet of habitable floor area. Woodinville's definition subtracts vehicle-parking area, covered and uncovered open-air floors, and floor area below five feet of ceiling height.
Height
The current ADU section applies the underlying zone's development standards and does not create a lower citywide DADU height cap. Confirm the zone and the applicable building-height and measurement provisions.
Setbacks
The underlying zone setbacks apply to new construction. A detached ADU may reduce the setback to zero at a property line abutting a dedicated public alley. A legally established enclosed structure may be converted even if its existing setback is nonconforming.
FAR, lot coverage, or impervious area
A new ADU must fit the zone's building coverage, landscaping, and other development standards. R-1 building coverage varies with actual lot area, and trees, critical areas, shoreline, grading, drainage, and access can be more limiting than the nominal yard.

Official sources: WMC 21.41.020: accessory dwelling units · WMC 21.32: development standards

Parking, occupancy, renting, and separate sale

Parking
WMC 21.41.020 does not state a special ADU parking number. Apply the current parking chapter together with Washington's transit and lot-size limits, and ask the city to confirm how existing stalls and a conversion are credited.
Owner occupancy
The current ADU code does not require the owner to occupy a unit, consistent with state law.
Short-term rental
An ADU may not be rented for fewer than 30 consecutive nights.
Separate sale
State law prevents a city from prohibiting separate condominium conveyance solely because the unit began as an ADU. A fee-simple division must independently satisfy subdivision and lot standards.

Official sources: WMC 21.41.020: accessory dwelling units · RCW 36.70A.681: limits on local ADU regulation

Utilities, fire access, and the permit path

A building permit and any associated planning, tree, clearing/grading, drainage, fire, right-of-way, and utility approvals are still required. Serving utility districts, not only the city, control connection capacity, meters, side sewers, and charges.

  1. Confirm that the current use table allows the ADU on the parcel and count every dwelling on the parent lot.
  2. Apply the base-zone setbacks, height, building coverage, landscaping, parking, tree, critical-area, drainage, and access standards to the proposed configuration.
  3. Ask the serving water and sewer districts to confirm capacity, meter, connection, and fee treatment.
  4. Submit the building permit and every associated site, tree, fire, utility, and right-of-way application with coordinated plans.
  5. Complete inspections and any condominium or land-division approvals before occupancy or separate conveyance.

Official sources: Woodinville permits and applications · WMC 21.41.020: accessory dwelling units

Rules that can change the answer for one property

A citywide ADU allowance does not prove that a detached unit fits on a particular lot. Resolve these items before buying plans or fixing the DADU location.

  • The two-ADU allowance still depends on the use table and parent-lot unit-count rules.
  • Only a legally established existing enclosed structure receives the conversion protection for nonconforming setback or building coverage.
  • R-1 building coverage changes with actual lot area; using the wrong coverage tier can produce a false fit result.
  • Required landscaping and tree credits must remain after the detached footprint, driveway, parking, and construction access are placed.
  • Critical areas, buffers, shorelines, slopes, drainage, easements, and utility routes can displace the apparent backyard envelope.

Official sources: WMC 21.32: development standards · WMC 21.50: tree protection

Prepared for a future address check

What a reliable DADU feasibility screen must verify

Woodinville is suitable for a detailed DADU screen once the engine combines the current use table, parent-lot unit count, 300–1,500-square-foot range, existing-structure status, zone bulk standards, R-1 lot-area coverage tier, landscaping, trees, and environmental layers.

Jurisdiction and zoning

Confirm the address is actually governed by Woodinville and select the correct base-zone standards.

Existing and proposed units

Count the principal dwelling, existing legal ADUs, middle-housing units, and the proposed attached or detached configuration.

Surveyed parcel geometry

Use legal lot lines, front/rear designation, alleys, access easements, and existing structures rather than a tax-map rectangle.

Capacity calculations

Test the ADU against the rules that apply locally: FAR or GFA, building or lot coverage, impervious or hard surface, and landscaping.

Mapped and field constraints

Screen critical areas and buffers, shorelines, slopes, flood hazards, significant trees, drainage, and recorded easements.

Utilities and emergency access

Verify water, sewer or septic, fire flow, hydrant and apparatus access, power, meters, and trench routes.

A conversion should only receive the nonconforming-setback or coverage treatment when permit history shows the enclosed structure and nonconformity were legally established. The screen must not infer that from aerial imagery alone.

Do not rely on the older rule

Older Woodinville materials may still describe one ADU, a smaller cap, or owner occupancy. WMC 21.41.020 was replaced by Ordinance 792 in 2025 and now allows two ADUs, 300 to 1,500 square feet of habitable area, and no owner-occupancy mandate.

Primary sources

Official Woodinville and Washington references

These are the sources used for this guide. Check them again before filing because ordinances, fee schedules, and permit forms can change.

WMC 21.41.020: accessory dwelling unitsCurrent count, configurations, size, alley, conversions, frontage, accessibility, and short-term-rental rules.WMC 21.32: development standardsCurrent zone setbacks, height, building coverage, and landscaping requirements.WMC 21.50: tree protectionTree permits, credits, replacement, protection, and development review.Woodinville permits and applicationsCurrent permit portal, forms, submittal information, and staff contacts.Woodinville Municipal CodeCurrent codified code and amendment status.RCW 36.70A.681: limits on local ADU regulationWashington's current baseline for two ADUs, size, height, parking, owner occupancy, conversions, alleys, fees, and critical-area exceptions.

A practical first-pass checklist

  1. 1

    Confirm the parcel is inside Woodinville city limits and identify its current zone.

  2. 2

    Map the principal home, lot lines, easements, trees, utilities, driveway, critical areas, and buffers on one current survey.

  3. 3

    Test the ADU footprint against setbacks, height, floor-area or coverage limits, hardscape, parking, and construction access.

  4. 4

    Ask the utility providers to confirm water, sewer, power, meter, side-sewer, and capacity requirements before fixing the design.

  5. 5

    Have the city confirm the complete land-use, building, fire, right-of-way, tree, and utility permit list in writing.