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. Seattle has been loosening ADU rules since 2019 to allow more housing in single-family zones.

Why it matters: ADUs are one of the gentlest ways to add housing in existing neighborhoods without changing their character dramatically. They’re a key part of Seattle’s strategy to add “missing middle” housing.

See also: DADU, Missing Middle Housing

Learn more: Seattle SDCI: Accessory Dwelling Units | Seattle OPCD: Encouraging Backyard Cottages


Design Review#

A public process where volunteer boards and city staff evaluate the design of proposed multifamily and commercial buildings. Seattle has eight geographic design review boards that hold public meetings to review projects exceeding certain size thresholds.

Why it matters: Design review can add 1-2 years to project timelines and significantly affect housing costs. The process gives neighbors a voice in shaping development but has been criticized for delays and subjectivity. Washington’s HB 1293 (2025) requires “clear and objective” design standards, forcing Seattle to overhaul its program.

See also: MUP

Learn more: Seattle SDCI: Design Review Program | The Urbanist: Fixing Seattle’s Design Review Process


Displacement#

The involuntary movement of residents from their homes or neighborhoods due to rising costs, redevelopment, or other economic pressures. Often disproportionately affects low-income communities and communities of color.

Why it matters: Displacement is the central equity concern in Seattle planning debates. The city’s rapid growth has pushed many long-time residents out of neighborhoods like the Central District and Chinatown-International District. Anti-displacement strategies – from community land trusts to tenant protections – are now required elements of comprehensive planning.

See also: Equitable Development Initiative, Community Land Trust

Learn more: Seattle OPCD: Anti-Displacement Framework (PDF) | The Urbanist: Community Resident Preference Policy


DADU (Detached Accessory Dwelling Unit)#

An ADU that’s a separate structure from the main house – typically a backyard cottage. As of 2019, Seattle allows both an attached ADU and a DADU on most single-family lots.

See also: ADU

Learn more: Seattle SDCI: Accessory Dwelling Units


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. When people talk about “upzoning,” they often mean increasing the allowed FAR.

See also: Upzoning, Zoning

Learn more: Planetizen: What Is Floor Area Ratio?


Cost Burden / Rent Burden#

A household is cost-burdened when it spends more than 30% of its gross income on housing costs (rent or mortgage plus utilities). A household spending more than 50% is considered severely cost-burdened. These thresholds are set by HUD and used across federal, state, and local housing programs.

Why it matters: About 46% of renter households in Seattle are cost-burdened, according to the National Low Income Housing Coalition. Cost burden is the standard metric for measuring housing affordability at the household level and is used to justify investments in affordable housing production, rental assistance, and tenant protections. When advocates say Seattle has an affordability crisis, cost burden data is typically the evidence.

See also: Affordable Housing, AMI

Learn more: Seattle Office of Housing: Data and Reports | NLIHC: Housing Needs in Washington


Grand Bargain#

The 2015 agreement between Seattle developers, affordable housing advocates, and labor groups that created the framework for Mandatory Housing Affordability (MHA). Developers agreed not to oppose inclusionary zoning requirements in exchange for upzones allowing additional building height and density.

Why it matters: The Grand Bargain was a pivotal political compromise that shaped Seattle’s housing policy for a decade. Understanding it explains why MHA exists, why certain neighborhoods got upzoned, and why affordable housing requirements were set at specific levels (5-7% of units or in-lieu fees).

See also: HALA, MHA

Learn more: Seattle HALA: Director’s Report (PDF) | The Urbanist: A Brief History of MHA


HALA (Housing Affordability and Livability Agenda)#

Seattle’s 2015 comprehensive housing policy framework, developed by a 28-member advisory committee convened by Mayor Ed Murray. HALA produced 65 recommendations aimed at creating 50,000 new housing units over 10 years, including 20,000 affordable units.

Why it matters: HALA was the most significant housing policy initiative in Seattle’s recent history. It created MHA, reformed ADU rules, expanded urban villages, and set the stage for current zoning debates. Many of today’s housing policies trace directly back to HALA recommendations.

See also: Grand Bargain, MHA, ADU

Learn more: Seattle HALA Report 2015 (PDF) | The Urbanist: Top HALA Recommendations


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. Larger cities near transit must allow up to six units per lot.

Why it matters: HB 1110 is a watershed moment for Washington zoning. It overrides local single-family zoning restrictions that have limited housing supply for decades. Seattle had to comply by June 2025, leading to the city’s biggest zoning overhaul since the 1990s. The law fundamentally changes what can be built in formerly single-family neighborhoods.

See also: Missing Middle Housing, Neighborhood Residential, Single-Family Zoning

Learn more: WA Commerce: Planning for Middle Housing | The Urbanist: Seattle Just Rezoned Entire City


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 is one of the most sweeping ADU reforms in any state, making it significantly easier to add “gentle density” across Washington. 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. Combined with HB 1110’s middle housing requirements, this fundamentally expands what can be built on residential lots.

See also: ADU, DADU, HB 1110

Learn more: WA Legislature: HB 1337 | The Urbanist: ADU and Design Review Reforms Pass


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 Floor Area Ratio (FAR). Within a quarter-mile of bus rapid transit stops, cities must allow at least 2.5 FAR. The law includes affordability requirements (10% of units at 60% AMI or 20% at 80% AMI) paired with a 20-year property tax exemption.

Why it matters: HB 1491 is one of the largest state-mandated upzones in U.S. history, requiring significant density increases around every major transit station in the Puget Sound region. The law ensures that billions invested in Link light rail expansion will be paired with housing capacity around stations – addressing past failures where transit investments didn’t produce expected ridership or housing growth. Compliant buildings must maintain affordability for 50 years.

See also: TOD, FAR, ST3

Learn more: WA Legislature: HB 1491 | The Urbanist: State Senate Greenlights TOD Housing Bill


Just Cause Eviction#

A legal framework that prohibits landlords from terminating a tenancy or evicting a tenant without one of the specific reasons enumerated in law. Seattle’s Just Cause Eviction Ordinance (SMC 22.206.160C), passed in 1980, lists 16 permitted reasons including nonpayment of rent, lease violations, owner occupancy, and demolition. Washington State enacted statewide just cause eviction through HB 1236 in 2021 (RCW 59.18.650).

Why it matters: Just cause eviction is the foundation of tenant stability in Seattle. Without it, landlords could end tenancies for any reason or no reason, leaving renters vulnerable to retaliation or displacement. Seattle’s ordinance was one of the earliest in the country and has been expanded over time — most recently in 2021, when landlords became required to offer lease renewals unless they have just cause not to. Understanding what qualifies as just cause helps renters know their rights and helps advocates evaluate proposed changes to eviction law.

See also: Displacement, Rent Stabilization

Learn more: Seattle SDCI: Just Cause Eviction Ordinance | Tenants Union: Just Cause Eviction Protection


Lot Coverage#

The percentage of a lot that can be covered by buildings and structures. Seattle’s neighborhood residential zones typically have lot coverage limits of 35-50% depending on the zone and housing type.

Why it matters: Lot coverage limits, along with setbacks and height limits, determine how much building can fit on a site. When you hear debates about building “too big” for a lot, lot coverage is often part of the equation. Recent zoning changes have adjusted lot coverage rules to accommodate middle housing.

See also: FAR, Setbacks, Zoning

Learn more: Seattle SDCI: Lot Coverage Standards (Tip 220) | The Urbanist: Seattle Just Rezoned Entire City


MHA (Mandatory Housing Affordability)#

Seattle’s program requiring developers of commercial and multifamily buildings to include affordable units or pay into a fund for affordable housing. Passed in 2019 alongside upzones in many neighborhoods.

Why it matters: MHA is Seattle’s main mechanism for connecting new development to affordable housing production. It’s controversial – developers say it raises costs; advocates say it doesn’t go far enough.

See also: Upzoning, Affordable Housing

Learn more: Seattle Office of Housing: MHA Program | Seattle SDCI: MHA Code


Missing Middle Housing#

Housing types between single-family homes and large apartment buildings: duplexes, triplexes, fourplexes, townhouses, courtyard apartments. Historically banned in most Seattle residential zones.

Why it matters: Seattle’s 2024 comprehensive plan update and related zoning changes are opening up much of the city to missing middle housing for the first time in decades. This is one of the biggest zoning shifts in the city’s history.

See also: ADU, Upzoning

Learn more: The Urbanist: Seattle Just Rezoned Entire City | Sightline: Seattle Deserves a Better Comp Plan


Neighborhood Residential (NR)#

Seattle’s new zoning designation that replaced “single-family” zones in 2021. NR zones (NR1, NR2, NR3) now allow various housing types including duplexes, triplexes, and other middle housing following HB 1110 implementation.

Why it matters: The name change was initially symbolic, but NR zones now permit significantly more housing than old single-family zones. NR1 allows the most density (smallest minimum lot sizes), while NR3 is the least dense. Understanding NR zoning is essential for following current development patterns and zoning debates.

See also: Single-Family Zoning, HB 1110, Missing Middle Housing

Learn more: Seattle OPCD: Neighborhood Residential Zoning | The Urbanist: Seattle Just Rezoned Entire City


Parking Minimums#

Zoning rules that require developers to build a minimum number of off-street parking spaces. Seattle eliminated parking minimums near frequent transit in 2012 and expanded reforms in 2018, but requirements remain in lower-density neighborhoods.

Why it matters: Parking minimums add significant costs to housing construction (roughly $30,000-$50,000 per space for structured parking). Studies found Seattle’s 2012 reforms resulted in 18,000 fewer spaces built, saving over $500 million. Washington’s 2025 parking reform law (SB 5184) now caps how much parking cities can mandate statewide.

See also: TOD

Learn more: Seattle SDCI: Parking Rules | The Urbanist: Seattle Passes Parking Reform


Racially Restrictive Covenants#

Private deed restrictions that barred non-white residents (and sometimes Jewish residents) from purchasing or occupying homes. The University of Washington’s Racial Restrictive Covenants Project has documented more than 50,000 such covenants in western Washington. The first known Seattle covenant was written in 1923; organized campaigns on Capitol Hill added racial restrictions to nearly 1,000 existing deeds in the late 1920s.

Why it matters: Covenants were the primary mechanism of residential segregation in Seattle after the Supreme Court struck down explicit racial zoning in 1917. They confined Black, Asian, and Native American families to narrow corridors — primarily the Central District and Chinatown-International District — while white-only neighborhoods accumulated wealth through homeownership. Though unenforceable after 1948 (Shelley v. Kraemer) and prohibited by the 1968 Fair Housing Act, the demographic and wealth patterns they created persist today. Washington passed the Covenant Homeownership Account Act (HB 1474) in 2023 to provide homeownership assistance to affected families.

See also: Redlining, Displacement, Single-Family Zoning

Learn more: UW Racial Restrictive Covenants Project | The Urbanist: Seven Maps That Capture Seattle’s Segregation


Redlining#

The practice of denying or restricting mortgage lending, insurance, and other financial services in neighborhoods based on racial or ethnic composition. In 1936, the federal Home Owners’ Loan Corporation (HOLC) drew “residential security maps” for Seattle, grading neighborhoods from A (“Best”) to D (“Hazardous”). Race was a central factor — the Central District received a D grade and was described as the “Negro area of Seattle.”

Why it matters: Redlining systematically denied wealth-building opportunities to communities of color for decades, and its effects are measurable today. A 2023 University of Washington study found that modern air pollution disparities in Seattle mirror the 1936 redlining maps, with previously redlined areas showing ultrafine particle concentrations 49% above average. The neighborhoods that received the lowest HOLC grades — Georgetown, South Park, the Central District — remain among Seattle’s most environmentally burdened and lowest-income areas. Understanding redlining is essential context for current equity frameworks, displacement patterns, and environmental justice work.

See also: Racially Restrictive Covenants, Displacement

Learn more: Seattle City Archives: Redlining in Seattle | The Urbanist: Seven Maps That Capture Seattle’s Segregation


Rent Stabilization#

A policy that limits how much landlords can increase rent within a defined period. Washington’s HB 1217, signed into law on May 7, 2025, caps annual rent increases for existing tenants at 7% plus the Consumer Price Index (CPI), or 10%, whichever is lower. Manufactured home rents are capped at 5% per year. The law exempts new construction for 12 years and owner-occupied small properties.

Why it matters: Washington became the third state (after Oregon and California) to enact statewide rent stabilization, ending a 1981 ban on local rent caps. The law establishes a ceiling on annual rent increases statewide, giving renters more predictability. Seattle layers additional local protections on top, including a 180-day notice requirement for rent increases (vs. 90 days statewide) and Economic Displacement Relocation Assistance for increases of 10% or more. The residential rent caps sunset after 15 years; manufactured home caps are permanent.

See also: Just Cause Eviction, Displacement, Affordable Housing

Learn more: WA Legislature: HB 1217 | The Urbanist: Rent Stabilization Becomes Law


SB 5184 (Parking Reform)#

Washington’s 2025 statewide parking reform law that caps the 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: Parking mandates have been one of the biggest hidden costs in housing development, adding $30,000-$50,000 per stall for structured parking. By capping how much parking cities can require, SB 5184 allows developers to build more housing on the same land at lower cost. This is one of the most comprehensive statewide parking reforms in the country and directly addresses a key barrier that has inflated Seattle-area housing costs for decades.

See also: Parking Minimums, TOD

Learn more: WA Legislature: SB 5184 | The Urbanist: Parking Reforms Become Law


Setbacks#

Required distances between buildings and lot lines (front, side, and rear). Seattle’s neighborhood residential zones typically require 20-foot front setbacks, 5-foot side setbacks, and rear setbacks of 20% of lot depth or 25 feet (whichever is less).

Why it matters: Setbacks, along with lot coverage and height limits, determine where and how big you can build on a lot. Recent zoning reforms have adjusted setbacks to make middle housing more feasible – for example, reducing front setbacks to allow “Seattle Six” configurations with stoops and covered porches.

See also: Lot Coverage, Zoning

Learn more: Seattle SDCI: Lot Coverage, Height and Yard Standards (Tip 220) | The Urbanist: Seattle Just Rezoned Entire City


Single-Family Zoning#

Zoning that only allows one house per lot. Seattle had roughly 75% of its residential land zoned single-family until recent reforms. The city has been gradually renaming and reforming these zones (now called “Neighborhood Residential”) to allow more housing types.

Why it matters: Single-family zoning is the legacy framework that restricted density across most of Seattle. Understanding its history and recent reforms is essential for following current zoning debates.

See also: Missing Middle Housing, Upzoning

Learn more: Seattle OPCD: Neighborhood Residential Zoning | Cascade PBS: Seattle shares plan for more housing density


Stacked Flats#

A middle housing type consisting of dwelling units stacked vertically in a building of no more than three stories, where each unit occupies a single floor. Unlike townhouses where units are side-by-side, stacked flats place units on top of each other, often sharing a central entrance or having individual street-level entries.

Why it matters: Stacked flats were historically common in Seattle but became difficult to build due to zoning restrictions and financing challenges. Washington’s HB 1110 explicitly includes stacked flats in the definition of middle housing that cities must allow. Seattle’s 2025 zoning reforms created incentives for stacked flats, including FAR bonuses (up to 1.4 on larger lots near transit). Because stacked flats can provide more units than townhouses on the same lot size, they’re a key housing type for meeting density goals while maintaining neighborhood scale.

See also: Missing Middle Housing, HB 1110, FAR

Learn more: WA Commerce: Middle Housing Model Ordinances | The Urbanist: The Deck is Stacked Against Stacked Flats


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: Upzoning is one of the most debated topics in Seattle land use. Proponents say it’s essential for housing affordability and climate goals. Opponents worry about neighborhood character, displacement, and infrastructure strain.

See also: FAR, MHA, Single-Family Zoning

Learn more: The Urbanist: Will Seattle Embrace Multiplexes? | Sightline: Seattle, a Model for Low-Sprawl Urban Growth


Affordable Housing#

Housing where residents pay no more than 30% of their income on rent/mortgage. In Seattle policy, “affordable” usually means affordable to households earning a percentage of Area Median Income (AMI) – often 60% or 80% AMI.

Why it matters: Seattle’s AMI is high (~$120k for a family of four), so “affordable at 80% AMI” still means rents that many people can’t afford. Understanding the AMI benchmarks helps you evaluate whether affordable housing proposals will actually serve the people who need them.

See also: MHA

Learn more: Seattle Office of Housing: Programs and Initiatives | Seattle Office of Housing: Income & Rent Limits


Community Preference Policy#

A voluntary policy (established by Executive Order 2019-02) that allows developers of City-funded affordable housing in high-displacement-risk areas to prioritize applicants with ties to the neighborhood — current residents, former residents, family members of former residents, or people with documented community connections.

Why it matters: Community Preference is one of Seattle’s primary tools for ensuring that new affordable housing serves the communities most affected by displacement. It was developed in response to advocacy by organizations including Interim CDA and El Centro de la Raza starting in 2015, and is designed to complement the Equitable Development Initiative. The policy must comply with federal, state, and local fair housing laws, and eligible areas are defined by the Office of Housing’s Geographic Boundary Map.

See also: Displacement, Equitable Development Initiative

Learn more: Seattle Office of Housing: Community Preference | The Urbanist: Community Resident Preference Policy


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