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Dream Dadu Rules

DADU Regulations King & Snohomish Counties

All information in this guide is for general reference only and should be verified during a formal feasibility review, as municipal codes are subject to change and site-specific conditions may apply.

For all the cities listed below, RCW 36.70A.681 is controlling law and supersedes conflicting local municipal codes. It does the following:

  • Overrides inconsistent local regulations.
  • Establishes statewide minimum rights for ADUs and DADUs.
  • Prohibits cities from using parking, size, owner-occupancy, or design standards to effectively block ADUs or DADUs.
  • Serves as the legal foundation for recent ADU/DADU code updates across Washington State.

The statewide floor (HB 1337): under RCW 36.70A.681, every city planning under the Growth Management Act must now allow two ADUs per lot, units of at least 1,000 sq ft, heights of at least 24 feet, and may not require owner occupancy — with parking mandates capped (and barred near major transit). Where an older city code conflicts, state law controls. Cities may still be more generous, and many now are:

Where Dream Dadu Builds

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  • Number of ADUs allowed: 2 per lot in addition to the principal home — attached, detached, or stacked, in any combination (including two DADUs)
  • Square feet allowance: 1,000 sq ft with up to two bedrooms — or 1,200 sq ft with three or more; up to 250 sq ft of attached garage doesn’t count
  • Height allowance: Same as the principal dwelling — up to 32 ft in Neighborhood Residential zones
  • Setbacks: Rear 5 ft (none at an alley); sides 5 ft average / 3 ft minimum
  • Parking requirements: None — no off-street parking required, citywide
  • Owner occupancy: Not required; DADUs may be sold separately as condominiums
  • SDCI offers pre-approved DADU standard plans that can shorten review.
  • Verified July 2026 against SMC 23.42.022 & SDCI guidance.
  • Dream Dadu builds here: see our Seattle DADU builder page.
  • Number of ADUs allowed: 2 per lot on any lot that allows a single-family home — attached, detached, or both. Detached ADUs are newly legal citywide as of July 1, 2025 (Ord. 6851)
  • Square feet allowance: Up to 1,200 sq ft, plus up to 300 sq ft of exempt parking/storage space; larger units possible for conversions of existing structures
  • Height allowance: 24 ft — or 28 ft when built as an addition over an existing accessory structure
  • Setbacks: Middle-housing standards (LUC 20.20.538): 5 ft sides, 10–15 ft rear by district; a DADU may be sited at a lot line abutting an alley
  • Parking requirements: None if the ADU is under 1,000 sq ft or within ½ mile of a major transit stop; otherwise 1 space
  • Owner occupancy: Not required (removed 2023); ADUs may be sold separately as condominiums
  • Verified July 2026 against Bellevue LUC 20.20.120.
  • Dream Dadu builds here: see our Bellevue ADU builder page.
  • Number of ADUs allowed: 2 ADUs or tiny homes on every residential lot — attached, detached, or both
  • Square feet allowance: Up to 1,000 sq ft (the Administrator may allow more on lots over 10,000 sq ft for affordable or public-benefit units)
  • Height allowance: A structure containing an ADU may reach the zone’s height max — 38 ft in Neighborhood Residential (ordinary accessory structures cap at 22 ft)
  • Setbacks: Side 3 ft, rear 5 ft, front 10 ft; a DADU may abut a lot line at an alley or right-of-way
  • Parking requirements: None — zero additional spaces required, citywide
  • Owner occupancy: Not required
  • Fire sprinklers are required in new detached ADUs.
  • Verified July 2026 against RZC 21.04.1110.
  • Dream Dadu builds here: see our Redmond DADU builder page.
  • Number of ADUs allowed: 2 per lot with a single-family home — attached, detached, or one of each
  • Square feet allowance: Detached ADUs up to 1,000 sq ft; attached ADUs up to 50% of the residence or 1,000 sq ft, whichever is larger
  • Height allowance: Detached ADUs up to 24 ft
  • Setbacks: 5 ft side and rear for stand-alone DADUs (structures combined with garages etc. use standard setbacks)
  • Parking requirements: None when the parcel already has four or more spaces — garage and driveway count
  • Owner occupancy: Not required
  • Septic lots need King County Public Health review, and removing significant trees requires a permit — plan both early.
  • Verified July 2026 against SMC 21.05.010 (eff. 1/1/2025).
  • Dream Dadu builds here: see our Sammamish DADU builder page.

Every Other City, A–Z

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  • Number of ADUs allowed: 2 per lot (state law overrides the city’s older one-DADU configuration limits)
  • Square feet allowance: Detached ADUs up to 1,000 sq ft, excluding garage and covered porches
  • Height allowance: 26 ft (accessory-building limit)
  • Setbacks: R4/R6: front 20 ft (25 ft on major streets), side 7 ft, rear 20 ft; accessory buildings of 650 sq ft or less may disregard rear/side setbacks
  • Parking requirements: 1 space per ADU in addition to the primary dwelling
  • Owner occupancy: Not required — the city’s older owner-occupancy certification is invalid under state law
  • Black Diamond’s published code predates HB 1337 — where they conflict, RCW 36.70A.681 controls.
  • Verified July 2026 against BDMC Ch. 18.56.
  • Number of ADUs allowed: 2 per lot (1 if the lot contains middle housing; 1 on critical-area lots)
  • Square feet allowance: Up to 1,200 sq ft; conversions of existing space may exceed this if no more than 40% of the primary unit’s floor area
  • Height allowance: Detached ADUs up to 30 ft — 33 ft when built over an existing accessory structure
  • Setbacks: Underlying zone standards; DADUs keep the same rear setback as primary structures, with alley provisions per BMC 12.14.060
  • Parking requirements: None — Bothell eliminated minimum off-street parking citywide in 2025
  • Owner occupancy: Not required
  • Verified July 2026 against BMC 12.14.135.
  • Number of ADUs allowed: 2 per lot (not on lots with a duplex or multifamily dwelling)
  • Square feet allowance: Up to 50% of the principal residence when it exceeds 2,000 sq ft — or up to 1,000 sq ft when the principal home is under 2,000 sq ft; 2 bedrooms max
  • Height allowance: Detached ADUs up to 25 ft
  • Setbacks: Same as single-family dwellings and garages in the underlying zone (CMC 15.48.070)
  • Parking requirements: 1 space per ADU, waived within ½ mile of a major transit stop; a pedestrian walkway to the ADU entrance is required
  • Owner occupancy: Not required
  • Verified July 2026 against CMC Ch. 15.46.
  • Number of ADUs allowed: 2 per principal dwelling, in any attached/detached combination, on all residential lots
  • Square feet allowance: Up to 1,000 sq ft — with no size limit when the ADU is wholly within a basement or attic
  • Height allowance: 24 ft
  • Setbacks: Underlying zone standards; a DADU may be built to a property line abutting an alley
  • Parking requirements: First ADU: none. Second ADU: 1 space, unless within ½ mile walking distance of a major transit stop
  • Owner occupancy: Expressly not required; ADUs may be sold separately as condominium units
  • Verified July 2026 against CMC 18.35.335.
  • Number of ADUs allowed: 2 per principal dwelling in residential zones, exempt from underlying density
  • Square feet allowance: Detached ADUs up to 1,000 sq ft; an ADU within the house or above a garage may reach 1,500 sq ft
  • Height allowance: Detached ADUs up to 24 ft, measured to the eave
  • Setbacks: Underlying zone (street 10 ft, rear 15 ft; 5 ft accessory side); a DADU may sit on a lot line abutting a public alley, and setback-nonconforming conversions are allowed
  • Parking requirements: 1 space per ADU in addition to the primary dwelling’s spaces
  • Owner occupancy: Not required; separate sale of ADUs (condominium) is protected
  • Verified July 2026 against DMC Ch. 14.48 (Ord. 1336, eff. 6/30/2025).
  • Number of ADUs allowed: 2 per lot, in any combination of attached and detached
  • Square feet allowance: 1,200 sq ft in the RS-20, RS-12 and RS-10 zones; 1,000 sq ft in RS-8 and RS-6
  • Height allowance: Detached ADUs up to 24 ft
  • Setbacks: Street 15–25 ft and side 5–10 ft by zone; DADU rear setbacks 10–25 ft — reducible to 5 ft when the DADU is 15 ft or shorter, and 0 ft at a public alley
  • Parking requirements: First ADU: none. Second ADU: 1 space. No parking required within ½ mile of a major transit stop
  • Owner occupancy: Not required — the city no longer enforces old owner-occupancy covenants
  • Verified July 2026 against ECDC 16.20.050 (Ord. 4360).
  • Number of ADUs allowed: 2 per lot, in any attached/detached combination
  • Square feet allowance: Up to 1,000 sq ft each, excluding non-living areas; the principal home must be at least 25% larger than the largest ADU; conversions within existing structures may exceed the cap
  • Height allowance: Same height limit as the principal dwelling under the zone’s standards
  • Setbacks: Underlying zone standards; no rear setback where the rear yard abuts an unplowed public alley
  • Parking requirements: Per zone standards with tandem parking allowed; none required within ½ mile of a major transit stop
  • Owner occupancy: Not required
  • Verified July 2026 against Issaquah LUC 18.500.090 (Ord. 3092).
  • Number of ADUs allowed: 2 per lot (attached or detached) wherever single-family homes are permitted
  • Square feet allowance: Attached: 1,000 sq ft. Detached: 17% of the lot up to 1,500 sq ft on lots of 6,000+ sq ft, or 1,000 sq ft on smaller lots
  • Height allowance: Detached ADUs up to 35 ft — one story over a detached garage, or two stories built at ground level
  • Setbacks: Bulk standards of the principal unit; a DADU may sit at a property line abutting a public alley
  • Parking requirements: None — no additional off-street parking is required for ADUs
  • Owner occupancy: Not required; ADUs may even be sold individually
  • Verified July 2026 against KMC 18.73.100 (Ord. 25-0630, eff. 7/1/2025).
  • Number of ADUs allowed: 2 per lot, in any attached/detached combination
  • Square feet allowance: Up to 1,000 sq ft of gross floor area
  • Height allowance: Detached ADUs up to 24 ft (chimneys, antennas and railings may extend 4 ft above)
  • Setbacks: Attached ADUs follow zone setbacks; a DADU in the rear half of the lot may be within 2 ft of side/rear lines, with lot-line siting at unplowed public alleys
  • Parking requirements: None within ½ mile walking distance of a major transit stop; otherwise 1 space per ADU (the director may waive)
  • Owner occupancy: Not required
  • Verified July 2026 against KCC 15.08.350.
  • Number of ADUs allowed: Urban areas: 2 per lot, any combination. Rural/resource areas: 1 — detached only where there is one primary dwelling and the lot meets the zone minimum
  • Square feet allowance: 1,000 sq ft heated plus 1,000 sq ft unheated; urban lots may trade unused unheated allowance up to 1,500 sq ft heated. Basement ADU floor area doesn’t count toward the cap
  • Height allowance: The base height of the applicable zone (KCC 21A.12.030)
  • Setbacks: Underlying zone standards (typically 5 ft interior setbacks in urban residential zones)
  • Parking requirements: None — no additional off-street parking required
  • Owner occupancy: Not required — but a recorded notice on title identifying the unit as accessory is mandatory before permit approval
  • Verified July 2026 against KCC 21A.08.030 (County ADU guide, 2026).
  • Number of ADUs allowed: 2 per lot — one attached and one detached, or two of either type
  • Square feet allowance: Up to 1,200 sq ft of gross floor area (excluding up to 200 sq ft of covered decks/porches); the director may allow more for single-floor attached conversions
  • Height allowance: The underlying zone’s height limit (generally 25 ft above average building elevation)
  • Setbacks: Same as single-family dwellings in the zone; garages and DADUs without alley access may be within 5 ft of the rear line when the portion in the rear yard is 15 ft or shorter
  • Parking requirements: 1 space only on lots with more than one ADU — and waived when on-street parking exists within 600 ft or the lot is near frequent transit
  • Owner occupancy: Not required
  • Kirkland offers a pre-approved DADU plan program that can shorten design and review.
  • Verified July 2026 against KZC 115.07.
  • Number of ADUs allowed: 2 per lot
  • Square feet allowance: 50% of the primary residence’s living area or 1,200 sq ft, whichever is greater
  • Height allowance: Per residential zone standards
  • Setbacks: Front 10 ft, side 5 ft, rear 10 ft
  • Parking requirements: None within ½ mile walking of a major transit stop; otherwise 1 space per unit on lots of 6,000 sq ft or less, 2 per unit on larger lots
  • Owner occupancy: Not required (requirement struck in 2025)
  • Verified July 2026 against MVMC (Ord. O-25-849, June 2025).
  • Number of ADUs allowed: 2 per single-family dwelling (subject to unit density; not on middle-housing lots)
  • Square feet allowance: Up to 1,000 sq ft of gross floor area
  • Height allowance: 25 ft, or the maximum allowed for the primary unit, whichever is lower
  • Setbacks: Zone development standards; a DADU may be sited at a lot line abutting a public alley (unless the city plows it)
  • Parking requirements: 1 space in addition to the principal dwelling’s; excepted within ¼ mile of a major transit stop
  • Owner occupancy: Not required
  • Medina requires the lot to meet minimum size and be sewer-connected; ADUs are barred on critical-area/shoreline lots and may not be used as short-term rentals.
  • Verified July 2026 against MMC 16.34.020 (Ord. 1040, eff. 7/1/2025).
  • Number of ADUs allowed: 2 per lot, attached or detached
  • Square feet allowance: 220–1,000 sq ft (excluding garage), and no more than 80% of the primary dwelling’s square footage
  • Height allowance: Follows the principal unit’s development standards
  • Setbacks: Same as the principal dwelling; a DADU may be sited at a lot line abutting a public alley
  • Parking requirements: 1 space per unit on lots of 6,000 sq ft or less, 2 per unit on larger lots; none within ½ mile walking of a major transit stop
  • Owner occupancy: Not required (removed 2025); ADUs on unit lots may be sold separately
  • These are interim regulations — permanent code is expected after the city’s 2026 public engagement.
  • Verified July 2026 against MICC 19.02.030 (interim Ord. 25C-02).
  • Number of ADUs allowed: 2, subordinate to a single-family dwelling
  • Square feet allowance: 300–1,000 sq ft (the director may allow more when the ADU is entirely on a single floor)
  • Height allowance: Attached ADUs up to 30 ft; detached ADUs up to 24 ft
  • Setbacks: The zoning code’s setbacks for single-family residences in the zone
  • Parking requirements: 1 space per ADU; none within ½ mile of a major transit stop
  • Owner occupancy: Not required; ADUs may be rented or sold (condominium or unit-lot subdivision)
  • Verified July 2026 against NMC Ch. 18.31 (Ord. 2025-671).
  • Number of ADUs allowed: 2 per lot
  • Square feet allowance: Up to 1,000 sq ft (the old 800 sq ft / one-bedroom limits were repealed in 2025)
  • Height allowance: Detached ADUs up to 25 ft
  • Setbacks: Detached: 5 ft side, 10 ft rear; 10 ft side-street on corner lots; lot-line siting at unplowed public alleys
  • Parking requirements: Per the general parking code — state law caps ADU parking at 1 space and bars requirements near major transit
  • Owner occupancy: Not required; ADUs may be sold as condominiums
  • Verified July 2026 against NBMC 18.06 / 18.10 (Ord. 1825).
  • Number of ADUs allowed: 2 per lot, in any combination — two attached, two detached, or one of each (updated June 2025)
  • Square feet allowance: Up to 1,000 sq ft of gross floor area; single-floor conversions may exceed it (over 1,250 sq ft reclassifies as an attached dwelling)
  • Height allowance: Detached ADUs up to 24 ft
  • Setbacks: Side 25 ft in RC/R-1, 5 ft in R-4–R-8, 4 ft in R-10/R-14; rear 5 ft; lot-line siting at alleys; at least 4 ft from other residential structures
  • Parking requirements: 1 space per ADU; none within ½ mile walking of a major transit stop
  • Owner occupancy: Not required
  • Verified July 2026 against RMC 4-2-110C (Ord. 6160/6173, 2025).
  • Number of ADUs allowed: 2 per lot in single-family residential zones
  • Square feet allowance: Up to 1,000 sq ft of gross floor area
  • Height allowance: Underlying zone standards (no ADU-specific limit)
  • Setbacks: Underlying zone standards; minimum lot area does not apply to ADUs
  • Parking requirements: None within ½ mile of a major transit stop or on lots under 6,000 sq ft; otherwise per the parking chapter
  • Owner occupancy: Not required
  • Verified July 2026 against SMC 17.55.070 (Ord. 1279).
  • Number of ADUs allowed: 2 per parent lot
  • Square feet allowance: 300–1,500 sq ft of habitable floor area
  • Height allowance: Underlying zone standards
  • Setbacks: Underlying zone standards; a DADU’s setback may be reduced to zero along a property line abutting a dedicated public alley
  • Parking requirements: 1 stall per ADU; none required within ½ mile of a major transit stop
  • Owner occupancy: Not required — but ADU rentals under 30 nights are prohibited
  • Verified July 2026 against WMC 21.41.020 (Ord. 792, 2025).

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