Kirkland ADU and detached ADU rules

Can I build an ADU or DADU in Kirkland?

Kirkland generally allows up to two ADUs and offers preapproved DADU plans, but a backyard unit still has to pass the property's zoning, FAR, lot coverage, trees, critical areas, utilities, and fire-access checks. Compare an attached conversion with a detached unit early because each follows a different FAR, permit, and fire-code path. Current parking guidance and fees also require care.

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

Each ADU may usually contain up to 1,200 square feet. A new DADU uses the underlying zone's height, yards and coverage. Special rear/alley setback options and a partial FAR exclusion may help. The FAR exclusion requires placement behind the main house as defined by code. Residential-L shoreline properties are limited to one ADU. Fire, utility, permit and ownership paths depend on the layout.

Up to 2ADUs per principal homeResidential-L shoreline property is limited to one.

1,200 sq ftTypical maximum eachAn attached one-floor existing-space exception may be larger.

500 / 800Possible DADU FAR exclusionBy lot size, when the building qualifies as behind the main house.

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Common homeowner questions

Answers to common Kirkland ADU questions

Can I build an ADU or DADU on my Kirkland property?

Often, yes. Kirkland generally allows up to two ADUs, but Residential-L shoreline property is limited to one, and every proposal still needs the correct zone, shoreline, existing-unit, FAR, coverage, tree, critical-area, access, fire, and utility screen.

How large can a Kirkland ADU or DADU be?

The usual maximum is 1,200 square feet for each ADU. A narrow attached-unit exception can use more existing area on one floor, while the conditional 500- or 800-square-foot DADU FAR exclusion changes the floor-area calculation, not the ADU size limit.

Do Kirkland's preapproved DADU plans skip permit review?

No. A preapproved design can reduce building-design work, but it still needs a plan license, site adaptation, zoning and survey review, structural work, fire and utility decisions, drainage, trees, and the required permits for the actual property.

Does Kirkland require off-street parking for an ADU?

The controlling ordinance waives ADU parking within a half-mile of major transit and generally triggers one added space outside that area only when more than one ADU is proposed, with additional on-street and frequent-transit exceptions. The City's summary page currently conflicts with that adopted text, so obtain written confirmation before designing a stall.

What should I verify before buying a Kirkland DADU plan?

Check Kirkland GIS, then confirm the zone, current survey, FAR and lot coverage, structure position, regulated trees, critical areas, drainage, utility routes, fire access, frontage work, and fees. ADUs over 800 square feet can face impact fees for complete applications received on or after July 1, 2026.

Official sources: KZC 115.07: accessory dwelling units · Kirkland Ordinance O-4905 · Kirkland middle-housing and ADU adoption · KZC 115.42: floor area ratio · KZC 115.90: lot coverage · Kirkland preapproved DADU plans · Kirkland ADU permitting process · Kirkland building and fire-code scenarios · Kirkland ADU regulations · Kirkland GIS maps · Kirkland planning FAQ and tree resources · Kirkland 2025 Critical Areas Ordinance update · Kirkland 2026 fee-change notice

What is allowed on one lot

KZC 115.07 allows two ADUs with a single-family dwelling: two attached, two detached, or one of each. A DADU is a separate building without a common roof to the principal dwelling or attached ADU. A Residential-L shoreline lot is limited to one ADU, and shoreline placement and ownership rules apply.

Two attached or internal ADUs.
One attached and one detached ADU.
Two separate DADUs or two DADUs attached to one another, with different building/fire permit scenarios.
Conversion of a permitted existing structure, including a detached garage, without curing qualifying setback or lot-coverage nonconformity when it is not increased.

Official sources: KZC 115.07: accessory dwelling units · Kirkland Ordinance O-4905 · Kirkland middle-housing and ADU adoption

How much room the property may have for an ADU

Maximum size: Each ADU may contain up to 1,200 square feet of gross floor area. The Director may approve more when an attached ADU is entirely within existing gross floor area on one floor. Areas below five feet of ceiling height, uncovered rooftop decks and at-grade patios, and up to 200 square feet total of specified exterior elements are excluded under the current calculation rules.
Height: A new DADU uses the underlying zone's height limit and current grade/height method. Ordinance O-4905 removed ADUs from KZC 115.08's ordinary accessory-structure height and size limits, including the former relationship-to-primary-building cap. Preapproved-plan marketing and older summaries do not replace the parcel's current zone calculation; sloped lots require particular care.
Setbacks: The underlying single-family zone supplies the base front, side and rear yards. Without an alley, a DADU may project as close as five feet from the rear line when the portion in the rear yard stays at or below 15 feet above existing grade. With an alley, it may locate within five feet subject to eave and sight-distance rules. Historic-preservation-subdivision and shoreline placement requirements can override the simple backyard model.
FAR, lot coverage, or impervious area: The zone supplies FAR and lot-coverage limits. A detached ADU or garage behind the main house can exclude its first 500 square feet on lots under 8,500 square feet, or 800 square feet on larger lots. KZC 115.42 defines the rear plane. It no longer adds a fixed separation distance for this exclusion. Internal stairs or a ceiling over 16 feet can qualify for one 100-square-foot allowance per dwelling. Rooms over 16 feet also count twice. Coverage and the ADU size limit remain separate checks.

Official sources: KZC 115.07: accessory dwelling units · KZC 115.42: floor area ratio · KZC 115.90: lot coverage · Kirkland Ordinance O-4905

When the house is close to its floor-area limit

Could a rear DADU or garage make more room in your plans?

Possibly. Kirkland can leave part of a qualifying detached building out of the floor area ratio calculation. FAR compares counted floor area across all levels with the lot area. It is not the same as living space or the amount of ground covered by buildings.

This matters when the existing house uses most of the lot's allowance. A rear DADU may use less of the remaining FAR than its actual size suggests. Simply calling rooms an attached ADU does not provide Bellevue's broad attached-ADU exemption.

Conditional FAR exclusions under KZC 115.42
Feature	Potential exclusion	What to confirm
Rear detached ADU or garage, lot under 8,500 sq ft	First 500 sq ft	The accessory building must be behind the main house.
Rear detached ADU or garage, lot at least 8,500 sq ft	First 800 sq ft	Use the applicable lot area, not an estimate from a listing.
Internal stairs or a room over 16 ft tall	One 100 sq ft allowance per qualifying dwelling	Not one per floor or staircase. Tall rooms also have an extra counting rule.

What does “behind the house” mean?

Draw a plane along the back of the main building, at its farthest point from the front-facing street or access easement. The plane is parallel to that street or easement. The detached building must be behind that plane. A side-yard location is not automatically eligible.

The current FAR rule does not add the former fixed separation-distance requirement. Fire separation, access and other building rules still apply. For corner lots and unusual house shapes, ask the planner to confirm the front facade and rear plane.

Two stories and a two-story living room are different

A normal upper floor counts as floor area. A room with a ceiling over 16 ft counts at twice its actual floor area for FAR. For example, a 250 sq ft double-height living room adds another 250 sq ft to the calculation. After the single 100 sq ft allowance, that feature adds a net 150 sq ft compared with an ordinary-height room, if the allowance was not already used elsewhere in the dwelling.

Do not deduct every stair opening. Also do not claim one allowance for the stairs and another for the tall room. The code provides one combined allowance.

Keep these three limits separate

ADU size: The usual 1,200 sq ft maximum remains. A FAR exclusion is not permission for a larger ADU.
FAR: Count all applicable building areas, then apply only the exclusions supported by the design.
Coverage and placement: Roof area, paving, setbacks, trees, access and utilities can still prevent the design from fitting.

What if the ADU sits above a garage?

Prepare one area schedule for the whole detached building. Include both levels and identify parking, living space and any other area. Do not automatically claim the full detached exemption twice, once for the garage and again for the ADU. Confirm the allocation with Kirkland. Shared buildings and two-ADU layouts need the same care.

Qualifying accessory buildings permitted before March 6, 2007 have a separate exclusion path. Some below-grade space can also be excluded under the code's grade test. Neither is established by an assessor's year-built field or a “basement” label alone.

How the free study handles this

The ADU study compares one new two-story ADU with an internal staircase and no double-height room. It shows the remaining counted floor area separately from the stair allowance. For a detached option, it also shows potential capacity if the building qualifies for the rear-location exclusion. Size, coverage and mapped-space limits remain in the comparison.

The new-home study keeps the original total living-area target. It compares a qualifying stair allowance, a rear detached garage when requested, and shifting part of that target into a rear DADU. These are separate options, not savings to add together. An architect and the City still need to confirm the layout and area schedule.

Official sources: KZC 115.42: FAR calculation and exclusions · KZC 115.07: ADU size and development rules

Parking, occupancy, renting, and separate sale

Parking: The controlling 2025 ordinance requires no ADU parking within a half-mile of major transit. Outside that area, the ADU subsection requires one total added space only when more than one ADU is proposed, and waives it when qualifying on-street parking is available within 600 feet or frequent transit meets the stated condition. This conflicts with the current City webpage's statement that a first ADU needs one space; obtain written City confirmation and cite the ordinance.
Owner occupancy: No owner-occupancy requirement applies.
Short-term rental: Long- or short-term rental requires a Kirkland business license. The City states that a short-term rental must be on an owner-occupied property and registered under the current rental program.
Separate sale: Kirkland allows segregated ownership. One or more ADUs, except stacked ADUs, may use the current unit-lot subdivision path. Shoreline Residential-L prohibits separate ownership; shoreline M/H has additional permit and pedestrian-path requirements.

Official sources: Kirkland Ordinance O-4905 · Kirkland moving-in and rental guidance

Utilities, fire access, and the permit path

All ADU applications route through Public Works and MyBuildingPermit. Water meter/service, side sewer, King County wastewater capacity charge, one-curb-cut rules, drainage, frontage, turnaround and fire access must be evaluated. Permit and sprinkler paths differ materially among an attached ADU, separate DADU, two DADUs, or units attached to each other.

Confirm the exact base zone, shoreline environment, historic-subdivision status, legal structures, transit conditions, title and existing units.
Apply the current zone's setbacks, height, lot coverage and FAR together with the ADU rear/alley and partial-FAR-exclusion conditions.
Select the attached/detached configuration early because it determines number of building permits, residential-code occupancy, imaginary property lines, fire separation, water/sprinkler design and unit-lot options.
Submit through MyBuildingPermit with the site plan, survey, supplemental building form, registration/covenant, plumbing worksheet and all applicable geotechnical, tree, drainage, demolition, rodent and fire documents.
Confirm fees using the complete-application date; applications received on or after July 1, 2026 can owe park, fire and transportation impact fees when the ADU exceeds 800 square feet.

Official sources: Kirkland ADU permitting process · Kirkland building and fire-code scenarios · Kirkland 2026 fee-change notice

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.

Residential-L shoreline sites are limited to one ADU, and detached units must sit landward of the principal house in the shoreline environments specified by code.
The parking ordinance and the City's summary webpage conflict; use the adopted ordinance and obtain a written interpretation before designing a required stall.
The current fee notice supersedes older toolkit language claiming categorical ADU impact-fee exemptions.
The partial DADU FAR exclusion depends on lot area and placement behind the main house. Do not apply it to every detached unit or stack a second full exclusion for a garage in the same building.
Significant and off-site tree protection, wetlands, streams, lakes, flood areas, geologic hazards, access, turnaround, side sewer and frontage improvements can control feasibility.

Official sources: KZC 115.07: accessory dwelling units · KZC 115.42: floor area ratio · KZC 115.90: lot coverage · Kirkland planning FAQ and tree resources · Kirkland 2025 Critical Areas Ordinance update · Kirkland Ordinance O-4905

Address-level ADU feasibility

What to check before assuming a detached ADU will fit

Kirkland's study checks the zone, shoreline, lot area, FAR and coverage. It shows a conditional rear-DADU FAR comparison and the assumed internal-stair allowance separately. Placement, height, fire separation, utilities and permits still need their own checks.

Jurisdiction and zoning

Confirm the address is actually governed by Kirkland 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.

Existing areas must not be discounted twice. Shared buildings need an allocated area schedule. Qualifying pre-2007 buildings, below-grade exclusions, sloped-lot height, shoreline limits and fire access need manual confirmation.

Do not rely on the older rule

Do not rely on two older summaries: the City ADU regulations webpage presently describes one parking space for the first ADU outside transit even though the adopted ordinance only triggers one added space when more than one ADU is proposed; and older toolkit fee language misses the July 1, 2026 impact-fee change for ADUs over 800 square feet.

Primary sources

Official Kirkland 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.

Kirkland ADU regulationsCurrent City summary of unit count, size, form, ownership, setbacks, parking, and related topics; read with Ordinance O-4905 where they conflict.KZC 115.07: accessory dwelling unitsCurrent codified unit count, size, placement, conversion, parking, height, ownership, and special-site rules.KZC 115.42: floor area ratioCurrent FAR definitions, tall-space treatment, general exclusions, and the conditional 500/800-square-foot detached ADU or garage exclusion.KZC 115.90: lot coverageCurrent structure, driveway, parking, hardscape, gravel, and partial pervious-surface treatment.Kirkland Ordinance O-4905Controlling 2025 KZC 115.07, 115.08, FAR, rear/alley, parking, shoreline and related ADU amendments.Kirkland middle-housing and ADU adoptionOfficial adoption history and shoreline/state-law implementation context.Kirkland moving-in and rental guidanceCurrent licensing, registration, long-term and short-term rental guidance.Kirkland ADU permitting processMyBuildingPermit, submittal, survey, registration, review and inspection guidance.Kirkland building and fire-code scenariosConfiguration-specific permit, code occupancy, separation, sprinkler and water-service scenarios.Kirkland 2026 fee-change noticeOfficial July 1, 2026 ADU impact-fee change and the 800-square-foot exemption threshold.Kirkland planning FAQ and tree resourcesCurrent zoning, tree, critical-area, mapping and property-research links.Kirkland 2025 Critical Areas Ordinance updateCurrent wetland, stream, lake, habitat, flood and geologic-hazard adoption materials.Kirkland preapproved DADU plansLive design catalog, licensing, site-adaptation and review limitations.Kirkland GIS mapsOfficial zoning, parcel, aerial, critical-area, utility, and property-research maps.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.

What to check first

1
Confirm the parcel is inside Kirkland 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.

Practical worksheet

Put this guide to work

Worksheet updated September 11, 2026. This is a planning example. Regulatory sources and data have their own dates.

Compare the configurations before picking a floor plan

A basement conversion, an attached addition and a detached backyard unit can have the same target living area but very different constraints. A conversion depends on the existing structure and usable headroom. A detached unit may create more utility trenching, access and tree conflicts. A pre-approved plan still needs a site-specific fit check.

Option A: use existing space: Ask the designer to evaluate structure, moisture, light, exits, fire separation and system capacity. Verify that the existing work is lawful rather than relying on a listing description.
Option B: attach new space: Check how the new area is counted with the primary home, how the roof and structure connect and whether occupied construction is practical.
Option C: detach: Test the permitted location, building separation, access, utilities, drainage and construction route. Include the whole property in coverage and tree calculations.
Use and ownership: Confirm the proposed rental duration, occupancy, addressing, utility arrangement and any separate-sale path under the current local rules. An ADU permit is not a completed subdivision or condominium process.

Request comparable budgets with the same inclusions: design, studies, permits, site work, utility upgrades, building work, taxes and contingency. A price for the prefabricated unit or shell is not the complete installed project cost.