Everything homeowners ask about building an ADU in Kirkland — answered with 2026 data.
Yes, ADUs are allowed in Accessory use wherever a Detached Dwelling Unit is permitted in the low density zones RS, RSX, RSA, PLA 3C, PLA 6E and PLA 16 (KZC 15.20.060, Special Regulation PU-23). The WD II waterfront row does not carry PU-23, and PU-21 limits RSA 4 lots in the Goat Hill Overlay to one attached ADU. Middle-housing sites may add two attached ADUs (Chapter 113 KZC). Residential-L shoreline lots get one ADU; lots with designated critical areas or buffers lose the state floor (RCW 36.70A.681(4)). in Kirkland, WA. The maximum size for a detached ADU is 1,200 sq ft of gross floor area (KZC 115.07(4)), above the 1,000 sq ft floor in RCW 36.70A.681(1)(f). Not counted: area under 5 ft of ceiling, uncovered rooftop decks or at-grade patios, and up to 200 sq ft of other exterior elements. Ordinance 4905 took ADUs out of the KZC 115.08 accessory-structure cap. Floor area ratio still bites: only the first 500 sq ft (lot under 8,500 sq ft) or 800 sq ft (8,500 sq ft and up) of a detached ADU behind the house is exempt from F.A.R. (KZC 115.42(1)(c)-(d)). Attached ADUs can be up to Same 1,200 sq ft gross floor area cap. Where the attached ADU sits entirely within existing gross floor area on a single floor, the Planning and Building Director may allow more so the whole floor is used. 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 $325,000-$550,000. The cost per square foot averages $400-$650. Garage conversions are more affordable at $100,000-$225,000, while prefab ADUs cost $300,000-$450,000. Permit fees add 2026 building permit on valuation (KMC Table 3: $1,620 plus $8.22 per $1,000 over $100,000), plan review at 65% of it, a $101 + $0.01/sq ft energy-code fee and a 3.5% technology fee: about $5,700 on a $300,000 detached ADU before plumbing, fire and utility charges. Plan licence 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 gross floor area cap. Where the attached ADU sits entirely within existing gross floor area on a single floor, the Planning and Building Director may allow more so the whole floor is used. Junior ADUs (JADUs) have a cap of Not a category in Washington; Kirkland's code has no junior ADU. The nearest equivalent is an attached ADU carved out of the existing house, which under KZC 115.07(6) may reuse an existing structure even if it violates current setbacks or lot coverage, so long as the nonconformity is not made worse. Maximum height is The single-family limit of your zone (KZC 115.07(5)): 25 ft above average building elevation in RS, PLA 3C and PLA 6E; 30 ft in RSX, RSA and PLA 16 (KZC 15.30.060). Ordinance 4905 removed ADUs from KZC 115.08, so the old accessory-structure cap of 15 ft above the house no longer applies. If you use the 5-ft rear setback, the part of the structure inside the required rear yard may be no taller than 15 ft above ABE (KZC 115.115(3)(o)(3)). State floor: 24 ft (RCW 36.70A.681(1)(g)). You are allowed up to Two ADUs per single-family dwelling: one attached and one detached, or two of either type on a qualifying lot.
Rear setback: 10 ft, the house standard (KZC 15.30.060), relaxed by KZC 115.115(3)(o): a detached ADU without alley access may sit 5 ft from the rear line if the part inside the required rear yard is no taller than 15 ft above ABE and the rear yard does not abut an access easement treated as a rear line; a detached ADU may extend to a rear line abutting an alley if its eaves stay on the lot and sight distance (KZC 115.135) is met (RCW 36.70A.681(1)(i)). A converted garage keeps its setbacks (KZC 115.07(6)). Side setback: Same as the house: 5 ft in the RS zones, with the two side yards totalling at least 15 ft (KZC 15.30.060, DD-9); a flat 5 ft in RSX and RSA. A detached ADU closer than 10 ft to another dwelling needs a fire-rated wall (City pre-approved DADU guide). State law bars ADU setbacks stricter than the principal unit's (RCW 36.70A.681(1)(h)). Front setback: 20 ft, the same front yard as the house, in RS, RSX, RSA, PLA 3C, PLA 6E and PLA 16 (KZC 15.30.060). On a corner lot only one front yard must be 20 ft; the other is treated as a side yard of 5 ft (DD-15) or, where the two fronts are essentially parallel, as a rear yard of 10 ft (DD-16). Note that garage conversions may be exempt from setback requirements if the existing structure is already within the setback area.
None. Ordinance O-4948 (passed Sept. 15, 2026, effective Sept. 26, 2026) rewrites KZC 115.07(7): ADUs are exempt from any minimum vehicle parking requirement, citywide, implementing SB 5184 (RCW 35A.21.445, no parking minimums for homes under 1,200 sq ft). Until then the rule was none within a half mile of a major transit stop (the STRIDE I-405 station) and one space only for a second ADU elsewhere; the city's ADU Regulations page still shows that older text, so cite O-4948 if asked for a space. 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; RCW 36.70A.681(1)(b) forbids it. An ADU may be segregated in ownership from the house (KZC 115.07(2)) and, except stacked units, placed on its own unit lot through a unit lot subdivision under KMC Title 22 (KZC 115.07(3); Ordinance 4907, June 2025). Exceptions: no separate ownership in the Residential-L shoreline environment; in the M/H shoreline environment it needs a Substantial Development Permit and a pedestrian pathway under KZC 83.420 (City ADU Regulations page). 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 About 3 months for a standard ADU permit, plus design and construction time (City Planning Your ADU page, 2026). A registered pre-approved DADU that qualifies for expedited review can be approved in as little as a few weeks; shoreline, geohazard and critical-area sites do not qualify. Plan check: Standard building plan review; intake covers the first review and one resubmittal, and each further review is billed at $179 an hour. The portion of a house converted to an ADU must meet current health and safety codes except that legally built habitable space need not meet IBC ceiling heights (KZC 115.07(8)). An ADU created without a finaled building permit needs an ADU inspection before a permit issues (KZC 115.07(9)(a)(3)). A detached unit closer than 10 ft to another dwelling needs a fire-rated wall detail, and fire sprinklers may be required after the Fire Department's fire-flow and access check. Pre-approved plans availability: Yes. The city's Pre-Approved Detached ADU Plans gallery lists four registered plan families from three local design firms, from a 476-636 sq ft one- or two-bedroom cottage to 1,000-1,132 sq ft two- and three-bedroom units, including a single-level no-stairs layout and mirrored versions. You license the plan from its designer (up to $1,000), staff attach the registered set to your permit so you submit no construction drawings, and a qualifying site gets expedited review. Custom plans remain allowed.
Average ADU rental income in Kirkland: 1-bedroom units rent for $2,450-$2,850/month, 2-bedroom units for $2,850-$3,350/month. Short-term rentals: Yes, with a Washington state and a City of Kirkland business licence, and the city's short-term rental page answers the ADU question directly: a registered detached ADU may be rented short-term (under 30 days) without li. Expected ROI: 6-9% gross rental yield on a $350,000-$550,000 detached build renting at $2,500-$3,300/mo, before vacancy, taxes, the new impact fee and financing; a conversion of existing space at $100,000-$225,000 yields roughly twice.
The minimum lot size for an ADU in Kirkland is No ADU-specific minimum: any lot that can hold a house can hold two ADUs (RCW 36.70A.681(1)(e); KZC 115.07 sets none). District minimums for the lot itself run from 3,800 sq ft in RSA 8 and 5,000 sq ft in RS 5.0 and RSX 5.0 to 35,000 sq ft in RS 35 and RSX 35 (KZC 15.30.060, DD-7 and DD-11). Floor area ratio, not lot size, is what usually squeezes a detached ADU on lots under 8,500 sq ft (KZC 115.42). 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 $100,000-$225,000. 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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