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
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Accessory dwelling units that are added to or included within the principal unit.
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Accessory dwelling units that are located in a detached structure.
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Maximum size of 1,200 square feet.1
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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).
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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.
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Must conform to development standards, i.e. lot coverage,setbacks, etc.,for single-family dwellings in the applicable use zone.1, 3, 4, 5
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Two ADUs: one required, with exceptions (available street parking within 600 feet or property is located within ½ mile of frequent transit).
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Allowed for DADUs. DADUs may not be subdivided from principle unit.6
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ADUs on lots created through small lot and historic subdivisions
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Allowed. DADUs on history lots must be located behind the historic residence.
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Required yards (setbacks):
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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.
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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.
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
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BUILDING CONFIGURATIONS
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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
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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
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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
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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
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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
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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
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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
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*plans shall also include a sprinkler riser diagram, shut-off, and Fire Department Connection (FDC).