Housing & Zoning Terms#
ADU (Accessory Dwelling Unit)#
A smaller, secondary home on the same lot as a main house. Think backyard cottages or basement apartments. Washington’s HB 1337 (2023) requires cities like Bothell to allow at least two ADUs per lot, with increased size limits and no owner-occupancy requirement.
Why it matters: ADUs are one of the gentlest ways to add housing in existing neighborhoods. Bothell’s updated code allows ADUs up to 1,200 square feet or 80% of the primary dwelling size, with parking requirements waived within a half-mile of transit.
See also: DADU, Missing Middle Housing, HB 1337
Learn more: Bothell Middle Housing Code Amendments | WA Legislature: HB 1337
DADU (Detached Accessory Dwelling Unit)#
An ADU that’s a separate structure from the main house – typically a backyard cottage. Under HB 1337, Bothell must allow both an attached ADU and a DADU on residential lots.
See also: ADU
Learn more: Bothell Middle Housing Code Amendments
FAR (Floor Area Ratio)#
The ratio of a building’s total floor area to the size of its lot. A FAR of 1.0 means you can build total floor space equal to the lot size (e.g., a one-story building covering the whole lot, or a two-story building covering half). Higher FAR = denser development allowed.
Why it matters: FAR limits are one of the main tools the city uses to control how big buildings can be in different zones. The Imagine Bothell Comprehensive Plan adjusts FAR in mixed-use zones to accommodate more growth. When people talk about “upzoning,” they often mean increasing the allowed FAR.
Learn more: Imagine Bothell Comprehensive Plan | Planetizen: What Is Floor Area Ratio?
HB 1110#
Washington’s 2023 statewide middle housing law requiring cities to allow duplexes, triplexes, fourplexes, and other “missing middle” housing types in residential neighborhoods. For cities of Bothell’s size (under 75,000), it requires at least duplexes on all residential lots, with more units allowed near transit.
Why it matters: HB 1110 overrides local single-family zoning restrictions that limited housing supply for decades. Bothell developed specific code amendments to implement the law, allowing a broader menu of middle housing types in all single-family zones while maintaining existing development rights for single-family homes.
See also: Missing Middle Housing, Single-Family Zoning
Learn more: WA Commerce: Planning for Middle Housing | Bothell Middle Housing Code Amendments
HB 1337 (ADU Reform)#
Washington’s 2023 statewide ADU law requiring cities to allow at least two accessory dwelling units (one attached, one detached) on any residential lot within urban growth areas. The law eliminates many local barriers including owner-occupancy requirements, excessive setbacks, and parking mandates for ADUs near transit.
Why it matters: HB 1337 makes it significantly easier to add “gentle density” in Bothell. The law enables homeowners to build backyard cottages or convert garages into housing without many of the restrictions that previously made ADUs expensive or infeasible. Bothell increased ADU maximum size from 800 sq ft to 1,200 sq ft or 80% of the primary dwelling.
Learn more: WA Legislature: HB 1337 | MRSC: Major Changes to Washington’s Housing Laws
HB 1491 (Transit-Oriented Development)#
Washington’s 2025 transit-oriented development law requiring cities to allow midrise housing near major transit stations. Within a half-mile of light rail, commuter rail, and streetcar stations, cities must permit at least 3.5 FAR. Within a quarter-mile of bus rapid transit stops, cities must allow at least 2.5 FAR.
Why it matters: With Stride BRT stations coming to Bothell along SR 522 and I-405, HB 1491 will require significant density increases around those stations. This ensures the regional investment in BRT infrastructure is paired with housing capacity. The law includes affordability requirements (10% of units at 60% AMI or 20% at 80% AMI) paired with a 20-year property tax exemption.
Learn more: WA Legislature: HB 1491 | The Urbanist: State Senate Greenlights TOD Housing Bill
Missing Middle Housing#
Housing types between single-family homes and large apartment buildings: duplexes, triplexes, fourplexes, townhouses, courtyard apartments, cottage housing, stacked flats. Historically restricted in most Bothell residential zones.
Why it matters: The Imagine Bothell Comprehensive Plan and state mandates (HB 1110) are opening up the city to missing middle housing types for the first time. Bothell’s code amendments allow but do not mandate these housing types, providing a broader “menu” of options while still permitting single-family homes under existing rules.
See also: ADU, HB 1110, Upzoning
Learn more: WA Commerce: Planning for Middle Housing | Bothell Plans Higher Density Citywide
Parking Minimums#
Zoning rules that require developers to build a minimum number of off-street parking spaces. Washington’s 2025 parking reform law (SB 5184) caps how much parking cities can mandate, limiting requirements to no more than 0.5 spaces per residential unit and prohibiting any parking minimums near frequent transit.
Why it matters: Parking mandates add significant costs to housing construction – roughly $30,000-$50,000 per space for structured parking. Bothell’s middle housing code allows parking requirements to be waived within a half-mile of transit stops, which affects areas near Stride BRT and Swift Green Line stations.
Learn more: WA Legislature: SB 5184 | The Urbanist: Parking Reforms Become Law
SB 5184 (Parking Reform)#
Washington’s 2025 statewide parking reform law that caps minimum parking requirements cities can impose on new development. Cities cannot require more than 0.5 parking spaces per residential unit. The law also prohibits any parking minimums near frequent transit, for senior housing, childcare facilities, small units, and existing buildings undergoing a change of use.
Why it matters: By capping how much parking cities can require, SB 5184 allows developers to build more housing on the same land at lower cost. For Bothell, this is particularly relevant around future Stride BRT stations and Swift Green Line stops where parking minimums are eliminated entirely.
See also: Parking Minimums, TOD
Learn more: WA Legislature: SB 5184 | The Urbanist: Parking Reforms Become Law
Single-Family Zoning#
Zoning that only allows one house per lot. Bothell, like most Washington cities, had the majority of its residential land zoned single-family until recent state reforms (HB 1110) required allowing additional housing types.
Why it matters: Single-family zoning is the legacy framework that restricted density across most of Bothell. Understanding its history and recent reforms is essential for following current zoning debates. Under HB 1110 and Bothell’s code amendments, these zones now allow a broader range of housing types.
See also: Missing Middle Housing, HB 1110, Upzoning
Learn more: Bothell Middle Housing Code Amendments | Sightline: How the WA Legislature Burst the Housing Abundance Dam
Upzoning#
Changing zoning rules to allow larger or denser buildings than previously permitted. Can mean increasing building height limits, FAR, or allowed unit counts.
Why it matters: The Imagine Bothell Comprehensive Plan includes significant upzoning in mixed-use zones and around transit corridors. State mandates like HB 1110 and HB 1491 effectively upzone areas near transit. Understanding upzoning helps you follow the core debates about Bothell’s future growth.
Learn more: Imagine Bothell Comprehensive Plan | Major Strides in Bothell’s 2024 Comp Plan
Affordable Housing#
Housing where residents pay no more than 30% of their income on rent/mortgage. In policy terms, “affordable” usually means affordable to households earning a percentage of Area Median Income (AMI) – often 60% or 80% AMI.
Why it matters: Bothell’s 2024 comprehensive plan identifies a need for 12,782 new homes over 20 years, with more than three-quarters needing to be affordable to people earning less than the area median income. With a median household income of approximately $132,000, understanding AMI benchmarks helps you evaluate whether housing proposals will actually serve the people who need them.
See also: AMI
Learn more: Imagine Bothell Comprehensive Plan | HUD: Income Limits
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