Woodinville ADU and detached ADU rules
Can I build an ADU or DADU in Woodinville?
Woodinville generally allows two ADUs from 300 to 1,500 square feet, including attached, stacked, and detached options. A legal existing garage can have a different path from a new DADU. For new construction, the base zone, lot-size coverage tier, trees, landscaping, critical areas, access, and utility service decide whether it fits.
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.
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Common homeowner questions
Answers to common Woodinville ADU questions
Can I build an ADU or DADU on my Woodinville property?
Often, yes. Woodinville allows up to two ADUs where the use table permits them, but the count is applied to the parent lot and the project must still meet zoning, coverage, landscaping, tree, critical-area, access, and utility requirements.
How large can a Woodinville ADU be?
The current range is 300 to 1,500 square feet of habitable floor area. Vehicle-parking area, open-air floors, and floor area with less than five feet of ceiling height are excluded from that ADU size definition.
Can I convert an existing garage into a Woodinville ADU?
Yes, when the enclosed structure was legally established and it can meet current building and life-safety requirements. Existing setback or building-coverage nonconformity may remain only if the conversion does not enlarge it, so verify the permit history before relying on this path.
What setbacks and height apply to a new Woodinville DADU?
The underlying zone controls the base yards and height; there is no single citywide DADU table. A property line along a dedicated public alley may allow a zero setback, but the current zone and lot-area coverage tier still need to be confirmed before design.
Can I use a Woodinville ADU as a short-term rental?
No. Woodinville's ADU code prohibits renting an ADU for fewer than 30 consecutive nights.
What should I map before choosing a Woodinville DADU plan?
Map the zone, actual lot-area coverage tier, existing buildings, required landscaping, regulated trees, critical areas, slopes, drainage, access, easements, and utility routes. Test those conditions together before purchasing or adapting a plan.
Official sources: WMC 21.41.020: accessory dwelling units · WMC 21.32: development standards · RCW 36.70A.681: limits on local ADU regulation · Woodinville Municipal Code · Woodinville maps · WMC 21.50: tree protection · Woodinville permits and applications
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
How much room the property may have for an ADU
- 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.
- Confirm that the current use table allows the ADU on the parcel and count every dwelling on the parent lot.
- Apply the base-zone setbacks, height, building coverage, landscaping, parking, tree, critical-area, drainage, and access standards to the proposed configuration.
- Ask the serving water and sewer districts to confirm capacity, meter, connection, and fee treatment.
- Submit the building permit and every associated site, tree, fire, utility, and right-of-way application with coordinated plans.
- 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
Address-level ADU feasibility
What to check before assuming a detached ADU will fit
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.
Confirm the address is actually governed by Woodinville and select the correct base-zone standards.
Count the principal dwelling, existing legal ADUs, middle-housing units, and the proposed attached or detached configuration.
Use legal lot lines, front/rear designation, alleys, access easements, and existing structures rather than a tax-map rectangle.
Test the ADU against the rules that apply locally: FAR or GFA, building or lot coverage, impervious or hard surface, and landscaping.
Screen critical areas and buffers, shorelines, slopes, flood hazards, significant trees, drainage, and recorded easements.
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.
What to check first
- 1
Confirm the parcel is inside Woodinville city limits and identify its current zone.
- 2
Map the principal home, lot lines, easements, trees, utilities, driveway, critical areas, and buffers on one current survey.
- 3
Test the ADU footprint against setbacks, height, floor-area or coverage limits, hardscape, parking, and construction access.
- 4
Ask the utility providers to confirm water, sewer, power, meter, side-sewer, and capacity requirements before fixing the design.
- 5
Have the city confirm the complete land-use, building, fire, right-of-way, tree, and utility permit list in writing.