Accessory Dwelling Units

ADU Market neighborhood

Overview

Accessory Dwelling Units (ADUs) are also known as in-law units, backyard cottages, secondary units and more. More specifically, an ADU is a subordinate residence either attached or detached to a single-family home.

ADUs offer housing opportunity for our community by:

  • Increasing housing affordability
  • Creating a wider range of housing options
  • Adding housing flexibility as families grow or change
  • Adding an income stream when families need it
  • Allowing seniors to stay near their families
  • Preserving neighborhood character

Common Questions

 

Can I building an ADU on my property?

You may be able to build up to two ADUs on your property. ADUs must meet zoning rules like setbacks, lot coverage, height, and floor area ratio. ADUs must also meet Building and Fire Codes. See ADU Regulations, Building and Fire Code Scenarios, and Public Works Facts and General Requirements for ADUs on this webpage for more information.

What is my zone?

You may find your property’s zoning two ways:

  1. Kirkland’s Zoning Map: This is a citywide map that describes the zoning classifications within Kirkland.
  2. Property Search: View through a map browser your property and get information such as permit history, King County Assessor’s information, zoning information, and more. You can also get a property report that includes information important when developing your property such as:
  • Zoning
  • Property Size
  • Sewer District, Water District
  • Stream, wetland, slopes and their buffers impacting your property
How do I apply for an ADU permit?

Application forms, instructions, and fees are found at the City’s Single Family & Duplex Permits webpage.

All permits can be applied for through MyBuildingPermit.

What are useful resources for designing an ADU?

If you are considering developing an ADU here are some useful links to resources outside of the City. Some information on these websites may not be consistent with Kirkland codes. Be familiar with Kirkland's regulations before submitting for a permit.

AARP’s All About Accessory Dwelling Units provides:

  • A Step by Step Guide to Design Development
  • Links to videos, articles, and other web resources.

A Regional Coalition for Housing (ARCH) provides:

  • Information on how to select an architect and contractor
  • An overview on lending assistance.

City of Seattle’s ADUniverse provides:

  • Links to over 160 DADU designs and designers
  • A step-by-step guide for creating an ADU

 

ADU Regulations

 

Definition

Attached ADU (AADU)

Accessory dwelling units that are added to or included within the principal unit.

Detached ADU (DADU)

Accessory dwelling units that are located in a detached structure.

Size/Scale

Maximum size of 1,200 square feet.1

FAR exemption for DADUs

Portion (500-800 sq. ft.) of square footage of DADU is exempt from FAR if located 10 feet from and behind the principal unit (see KZC115.42).

Number of ADUs

Two – both may be either attached or detached.2

Applicants planning on two attached ADUs should contact the Planning and Building Department at 425-587-3600 for additional Building Code assistance.

Location

Must conform to development standards, i.e. lot coverage,setbacks, etc.,for single-family dwellings in the applicable use zone.1, 3, 4, 5

Owner Occupancy

Not required

Parking

One ADU: none

Two ADUs: one required, with exceptions (available street parking within 600 feet or property is located within ½ mile of frequent transit).

Separate ownership

Allowed for DADUs. DADUs may not be subdivided from principle unit.6

ADUs on lots created through small lot and historic subdivisions

Allowed. DADUs on history lots must be located behind the historic residence.

Required yards (setbacks):

Same as underlying zoning. DADUs may be located within 5 feet of an alley. DADUs without alley access may be located no closer than 5 feet from the rear property line as long as the portion of the DADU in the reduced setback is no taller than 15 feet.

1 See additional size limitations for accessory structures in Kirkland Zoning Code (KZC) Section 115.08.

2 Any property within the Residential-L Shoreline Environment is only allowed one (1) ADU.   

3 Except as modified by KZC 115.42 and KZC 115.115.3.o. 

4 DADUs located on lots approved using the historic preservation subdivision regulations must be located behind the historic residence.   

5 DADUs shall be located landward of the principal residence on any property located within the Residential-L and M/H Shoreline Environments pursuant to KZC 83.200.3. 

6 Separate ownership is not allowed on properties within the Residential-L Shoreline Environment.  ADUs within M/H Shoreline Environment may have separate ownership subject to a Substantial Development Permit. Any ADU created within the M/H Shoreline Environment under separate ownership will require a pedestrian pathway meeting the requirements of KZC 83.420.

Building and Fire Code Scenarios

Note: In order to be considered an accessory dwelling unit, the occupants shall not be provided with an interior access between attached dwelling units.

CODE SCENARIOS

BUILDING CONFIGURATIONS

One Single-Family Residence (SFR) with one detached ADU – two total units

For purposes of building code compliance:

  • these will be reviewed as two one-family dwellings per International Residential Code (IRC)
  • an imaginary property line shall be used for fire separation requirements this will be two single-family building permits

 

 

 

 

SFR

 

ADU

 

 

 

 

 

One SFR with one attached ADU

For purposes of building code compliance:

  • this will be reviewed as a two-family dwelling per IRC
  • this will be one single-family building permit

 

 

 

SFR

ADU

 

 

One SFR with two attached ADUs (townhouse style) – three total units

For purposes of building code compliance:

  • this will be reviewed as townhouses per IRC
  • may need a National Fire Protection Association (NFPA) 13D sprinklers system based on gross floor area
  • Revised Code of Washington (RCW) 64.55 must be satisfied (a condo sale prohibition covenant can do this)
  • this will be one multifamily building permit

 

 

 

 

SFR

ADU

ADU

 

 

 

 

 

One SFR with two attached ADUs(stacked, non-townhouse style) – three total units

For purposes of building code compliance:

  • this will be reviewed as a multifamily apartment per International Building Code (IBC)
  • separate connection to the water main is needed for NFPA 13R sprinklers*
  • RCW 64.55 must be satisfied (a condo sale prohibition covenant can do this)
  • this will be one multifamily permit

 

 

 

 

SFR

ADU

 

 

ADU

 

 

 

One SFR with two detached ADUs (DADUs are not attached to each other)

For purposes of building code compliance:

  • these will be reviewed as three separate one-family dwellings per IRC
  • imaginary property lines shall used for fire separation requirements
  • these will be three single-family building permits

 

 

ADU

 

SFR

 

 

 

 

 

ADU

 

One SFR with two detached ADUs (DADUs are attached to each other)

For purposes of building code compliance:

  • these will be reviewed as a one-family dwelling and a two-family dwelling per IRC
  • an imaginary property line shall used for fire separation requirements
  • these will be two single-family building permits

 

 

 

 

SFR

 

ADU

ADU

 

 

 

 

One SFR with one attached ADU and one detached ADU

For purposes of building code compliance:

  • these will be reviewed as a two-family dwelling and a one-family dwelling per IRC
  • an imaginary property line shall used for fire separation requirements
  • these will be two single-family building permits

 

 

 

 

SFR

ADU

 

ADU

 

 

 

 

*plans shall also include a sprinkler riser diagram, shut-off, and Fire Department Connection (FDC).

Public Works Facts and General Requirements for ADUs

  1. Proposed Accessary Dwelling Unit (ADU) projects must meet all Kirkland Zoning Code (KZC) requirements, specifically KZC Chapter 115.07.
  2. All ADU permit applications (even an interior alteration) must be routed to Public Works for review.
  3. Impact Fees:
    • Transportation impact fees are exempted for ADU in accordance with KMC 27.04.050.
    • Park impact fees are exempted for ADU in accordance with KMC 27.06.050.
    • School impact fees are exempted for ADU in accordance with KMC 27.08.050.
    • Transportation, park, and school impact fees are assessed on the primary single-family residence (SFR) only. An existing SFR, whether remaining or demolished to construct a new SFR, will receive a credit for transportation, park, and school impact fees.
  4. Utility connection charges (i.e. capital facility charges) are assessed in accordance with the latest version of the Public Works Fee Schedule. All fee schedules may be found at the Development Services Fees webpage. 
    • Kirkland Water Capital Facility Charge and Cascade Water Alliance Regional Capital Facility Charge are determined by the meter size associated with a new service. ADUs are not subject to this charge if there are no changes to the water service/meter.
    • ADUs are not subject to Kirkland Sewer Capital Facility charges.
    • The King County Sewer Treatment Capacity Charge Residential form will continue to be used to report connections and reconnections of all dwelling units; the City does not determine the amount of County Capacity Charge that is owed.
    • ADUs are not subject to the Kirkland Surface Water Capital Facility Charge, if the primary residence is already connected to the public storm system.
  5. Required Public Improvements (i.e. half-street or frontage improvements) shall be determined in accordance with KZC 110.For the purposes of determining public improvements, an ADU project is classified as a single-family dwelling addition/alteration.Per KZC 110.70, public improvements are required if the total addition/alteration value exceeds $268,000, based on building construction (alteration) costs in effect on January 1, 2019. This threshold shall be reviewed annually and adjusted by a percentage equal to the percentage of increase in building construction costs.
  6. Access:
    • Only one driveway cut from the public street is allowed for the property / tax parcel.
    • The primary residence must maintain a 20x20 parking pad, unobstructed by site circulation providing access to the development / ADUs (i.e. driveways or drive aisle).
    • Vehicular turnaround(s) must be provided as a part of the site circulation design. Vehicles must be able to back out of garages and parking spots comfortably and to drive forward onto the public street.