Everything homeowners ask about building an ADU in Kirkland — answered with 2026 data.
Yes, ADUs are allowed in Permitted as an accessory use anywhere a Detached Dwelling Unit is allowed in the low density residential zones — RS 35, RS 12.5, RS 8.5, RS 7.2, RS 6.3, RS 5.0; RSX 35, RSX 12.5, RSX 8.5, RSX 7.2, RSX 5.0; RSA 1, 4, 6 and 8; and PLA 3C, PLA 6E and PLA 16 (Kirkland Zoning Code 15.20.060, Special Regulation PU-23 → KZC 115.07). Two exceptions in the local table run narrower than state law: the WD II waterfront zone's Detached Dwelling Unit row does not carry PU-23, and PU-21 limits RSA 4 lots in the Goat Hill Overlay Zone to one attached ADU. RCW 36.70A.681(1)(c) requires two ADUs in all zoning districts inside an urban growth area that allow single-family homes, so state law would override — except that RCW 36.70A.681(4) exempts lots designated with critical areas or their buffers. Confirm your own parcel with Kirkland Planning and Building at 425-587-3600 in Kirkland, WA. The maximum size for a detached ADU is 1,200 sq ft of gross floor area (Kirkland Zoning Code 115.07(4)) — 200 sq ft above the 1,000 sq ft floor state law guarantees (RCW 36.70A.681(1)(f)). Area with less than five feet of ceiling height, uncovered rooftop decks and at-grade patios, and up to 200 sq ft of other covered and uncovered exterior elements do not count. The practical catch is floor area ratio: only the first 500 sq ft of a detached ADU on a lot under 8,500 sq ft, or the first 800 sq ft on a lot of 8,500 sq ft or more, is exempt from F.A.R., and then only when the structure sits behind the main house (KZC 115.42). If F.A.R. would push your ADU below 1,000 sq ft, raise RCW 36.70A.681(1)(f) with the planner. Attached ADUs can be up to Same 1,200 sq ft cap. Where an attached ADU sits entirely within existing gross floor area on a single floor, the Planning and Building Director may allow more square footage in order to use the floor area efficiently. Kirkland has an ADU-friendliness score of 9/10. Check our full Kirkland ADU rules page for complete zoning details.
ADU construction in Kirkland 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 permit and plan review amounts with Kirkland Planning and Building at 425-587-3600 — no ADU fee schedule is published on the city's ADU Toolkit pages. If you use a pre-approved plan, budget separately for licensing it from the designer, which the city puts at up to $1,000 to your budget. See our detailed Kirkland ADU cost guide.
Detached ADUs in Kirkland can be up to 1,200 sq ft of gross floor area. Attached ADUs are limited to Same 1,200 sq ft cap. Where an attached ADU sits entirely within existing gross floor area on a single floor, the Planning and Building Director may allow more square footage in order to use the floor area efficiently. Junior ADUs (JADUs) have a cap of Not a category in Washington — Kirkland's code has no junior ADU designation. The nearest equivalent is an attached ADU carved out of the existing house. Maximum height is The height limit that applies to a single-family dwelling in your zone (Kirkland Zoning Code 115.07(5)) — 25 feet above average building elevation in the RS, PLA 3C and PLA 6E zones, and 30 feet above ABE in RSX, RSA and PLA 16 (KZC 15.30.060). State law bars any city from setting an ADU roof height limit below 24 feet unless the principal unit's own limit is lower (RCW 36.70A.681(1)(g)). Separately, if you use the five-foot rear setback allowance, the part of the structure inside the required rear yard may be no taller than 15 feet above ABE (KZC 115.115(3)(o)(3)). You are allowed up to 2 ADUs per single-family dwelling — one attached and one detached, two attached, or two detached on a qualifying lot.
Rear setback: 10 feet is the zone standard for a house (Kirkland Zoning Code 15.30.060), and an ADU takes the same. But KZC 115.115(3)(o) then relaxes it: a detached ADU without alley access may sit as close as five feet to the rear property line provided the portion inside the required rear yard is no taller than 15 feet above average building elevation and the rear yard does not abut an access easement regulated as a rear property line; and a detached ADU may extend all the way to a rear property line abutting an alley, so long as its eaves do not cross the line and it meets the sight-distance rule in KZC 115.135. State law separately requires alley-abutting lot line siting (RCW 36.70A.681(1)(i)). Side setback: The same side yard as the house — five feet in the RS zones, but the two side yards together must total at least 15 feet (Kirkland Zoning Code 15.30.060 and Special Regulation DD-9); a flat five feet in the RSX and RSA zones. State law bars setbacks for ADUs more restrictive than those for principal units (RCW 36.70A.681(1)(h)). Front setback: 20 feet, the same front yard as the house, in the RS, RSX, RSA, PLA 3C, PLA 6E and PLA 16 zones (Kirkland Zoning Code 15.30.060). On a corner lot with two required front yards, only one must be 20 feet — the other is regulated as a side yard in RSX and RSA (DD-15) or as a rear yard where the two fronts are essentially parallel (DD-16). Note that garage conversions may be exempt from setback requirements if the existing structure is already within the setback area.
None within one-half mile of a major transit stop (Kirkland Zoning Code 115.07(7); RCW 36.70A.681(2)(a)(i)). Read that carefully: the city's own ADU Regulations page states Kirkland's only current major transit stop is the STRIDE (I-405) bus rapid transit station, with future stops along King County Metro's RapidRide K Line once construction is under way. Beyond the half mile, KZC 115.07(7) requires one off-street space only where there is more than one ADU on the lot, and waives even that if on-street parking is available within 600 feet or the property is within half a mile of transit with 15-minute commute-hour headways. The city's ADU Regulations page describes the same rule as one space for the first ADU — the two readings differ, so confirm with Planning and Building at 425-587-3600. Either way state law caps what Kirkland may demand at one space per unit on lots under 6,000 sq ft and two per unit on larger lots (RCW 36.70A.681(2)(a)(ii)-(iii)). 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, and Kirkland could not require it if it wanted to — "the city or county may not require 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" (RCW 36.70A.681(1)(b)). Kirkland goes further: an ADU may be segregated in ownership from the single-family dwelling unit, and one or more ADUs other than stacked units may be subdivided within a unit lot subdivision (Kirkland Zoning Code 115.07(2)-(3)). The city's ADU Regulations page notes an exception for properties in the Residential-L Shoreline Environment. 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 Kirkland is typically Roughly 3 months for a standard ADU permit, with additional time for design and construction; a pre-approved DADU application takes less — the city says as little as a few weeks (City of Kirkland, Planning Your ADU and Explore Kirkland's Pre-Approved Plans). Plan check: Standard building plan review. The portion of a single-family dwelling in which an attached ADU is proposed must meet all applicable health and safety codes, except that space legally constructed as habitable space need not meet current International Building Code ceiling height requirements (Kirkland Zoning Code 115.07(8)). If an ADU was created without a finaled building permit, an ADU inspection is required before an ADU permit will issue (KZC 115.07(9)(a)(3)). Applicants planning two attached ADUs are told to call Planning and Building at 425-587-3600 for extra Building Code help. Pre-approved plans availability: Yes — Kirkland runs a Pre-Approved Detached ADU Plans program. The plans are drawn by architects and designers, pre-reviewed by the City for code compliance, and cover units under 600 sq ft, two-bedroom family layouts, single-level accessible plans and modern or eco-focused designs. You pick one from the city gallery, license it from the designer (up to $1,000), and have the designer adapt it to your site. Custom plans remain an option.
Average ADU rental income in Kirkland: 1-bedroom units rent for $1,950-$2,600/month, 2-bedroom units for $2,500-$3,300/month. Short-term rentals: Yes, with a city business license — and with real limits. Kirkland's business licence chapter defines "single-family residence" to include accessory dwelling units, both attached and detached (Kirkland Municipal Code 7.02.030(s)), so renting an ADU short-term or long-term requires a licence, and short-term rentals owe lodging excise tax (KMC 7.02.310). KMC 7.02.300 then adds special provisions for short-term rentals of detached dwelling units: unlimited when the owner or authorised agent continuously occupies part of the unit as a primary residence; capped at 120 days a year where the owner occupies it at least 245 days a year and a property manager is available within 15 miles; and never more than two short-term rental agreements in effect at a single detached dwelling unit at one time. Whether those day caps reach a detached ADU as opposed to the house itself is not settled on the face of the code — confirm with the City at 425-587-3600 before you list. Expected ROI: 5-7% annual return.
The minimum lot size for an ADU in Kirkland is No ADU-specific minimum. State law requires a city to allow an ADU on any lot that meets the minimum lot size for the principal unit (RCW 36.70A.681(1)(e)), and Kirkland's KZC 115.07 imposes none. The district minimum for the lot itself runs from 3,800 sq ft in RSA 8 and 5,000 sq ft in RS 5.0 and RSX 5.0 up to 35,000 sq ft in RS 35 and RSX 35 (Kirkland Zoning Code 15.30.060, Special Regulations DD-7 and DD-11). 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 Kirkland, 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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