HIP Tool: Inclusionary Zoning

Inclusionary zoning is a tool that stipulates that new residential development in certain zones include some proportion or number of affordable housing units, or meet some type of alternative compliance. In order to ensure that costs are offset, jurisdictions often increase the development rights (i.e., density) of a proposed project. Adopting this combination—mandatory affordable housing and increased density—into the local code a priori an actual development application distinguishes inclusionary zoning from other types of incentive zoning zoning may be applied in ownership and rental developments, single-family and multi-family zones, and can be tied to specific geographic areas. Jurisdictions should craft inclusionary zoning policies that best reflect the needs of their residents, paying close attention to details relating to program management and monitoring. In the state of Washington all units developed through an inclusionary zoning program must remain affordable for at least 50 years (RCW 36.70A.540).


Mandatory inclusion of affordable housing in residential developments is a response to persistently high housing costs and the difficulty of building lower-cost market-rate housing in many areas due to high land prices,and is an affordability strategy designed to secure a public benefit from growth. Jurisdictions may produce a nexus study to show the extent that new development generates a need for new affordable housing. Some jurisdictions choose mandatory programs over voluntary ones, based on conclusions that voluntary incentive programs face challenges in producing significant numbers of affordable housing units.

Before 2006 mandatory inclusionary housing requirements were used infrequently in Washington State due to concerns about takings challenges and the appearance of establishing a “tax.” However, amendments to the Growth Management Act in 2006 (RCW 36.70A.040) and other state laws allow jurisdictions to enact or expand affordable housing mandatory inclusionary zoning programs as long as they are tied to an upzone or other regulation changes that increases the area’s development capacity. For more detail, also see WAC 365-196-870.

Affordable housing must be mentioned explicitly as a public benefit to be rewarded with increased density, reduced parking, reduced fees or taxes or other incentives offered.

See density bonuses or incentive zoning for more information about state law, and voluntary inclusionary programs.

Tool Profile

Focus Areas

  • Urban Centers
  • Transit Oriented Development
  • Expensive Housing Markets
  • Innovative Single Family Techniques

Project Types

  • Single Family
  • Multifamily
  • Ownership
  • Rental
  • Market Rate

Affordability Level

  • 80% to 120% AMI
  • Less than 80% AMI

Housing Goal

  • Affordability