State Building Code.
 
The State Building Code (Code) establishes minimum performance standards and requirements for construction and construction materials in the state, consistent with accepted standards of engineering, fire, and life safety.  The Code comprises a number of model codes and standards, developed and published by international and national organizations, which are adopted by reference in the State Building Code Act (Act).  Model codes and standards adopted in the Act include the International Building Code, the International Residential Code, and the Uniform Plumbing Code Standards.
 
The International Building Code establishes minimum requirements for all buildings except detached one- and two-family dwellings and townhouses up to three stories.  The International Residential Code comprises all building, plumbing, mechanical, fuel gas, and electrical requirements for one- and two-family dwellings and townhouses up to three stories.
 
The State Building Code Council (Council) is responsible for adopting, amending, and maintaining the model codes and standards adopted by reference in the Act.  Amendments to the model codes and standards adopted by the Council are codified in the Washington Administrative Code.  The Council reviews updated editions of each model code and standard every three years.

Growth Management Act.

The Growth Management Act (GMA) is the comprehensive land use planning framework for counties and cities in Washington.  The GMA establishes land use designation and environmental protection requirements for all Washington counties and cities.  The GMA also establishes a significantly wider array of planning duties for 28 counties, and the cities within those counties, that are obligated to satisfy all planning requirements of the GMA.  These jurisdictions are sometimes said to be "fully planning" under the GMA.

The GMA directs fully planning jurisdictions to adopt internally consistent comprehensive land use plans that are generalized, coordinated land use policy statements of the governing body.  Comprehensive plans are implemented through locally adopted development regulations, and both the plans and the local regulations are subject to review and revision requirements prescribed in the GMA.  In developing their comprehensive plans, counties and cities must consider various goals set forth in statute.

The GMA also establishes 14 goals in a nonprioritized list to guide the development of comprehensive plans and development regulations of counties and cities that plan under the GMA.  Examples include urban growth, housing, and economic development goals.

State Environmental Policy Act.
 
The State Environmental Policy Act (SEPA) establishes a review process for state and local governments to identify environmental impacts that may result from governmental decisions, such as the issuance of permits or the adoption of land-use plans.  Except for development projects that are exempt from SEPA requirements, SEPA generally requires a project applicant to submit an environmental checklist.  The checklist includes answers to questions about the potential impacts of the project on the built environment and the natural environment.  Generally, an environmental impact statement (EIS) must be prepared for a proposal which the lead agency determines will have a probable significant and adverse impact on the environment.

The Department of Commerce must develop and administer a grant program to provide direct financial assistance to counties and cities for the adoption of preapproved middle housing plans.  A preapproved middle housing plan is a selection of middle housing architectural plans that have been reviewed by county or city code officials and approved for compliance with applicable building codes.  Middle housing is defined as duplexes, triplexes, fourplexes, fiveplexes, sixplexes, attached and detached accessory dwelling units, cottage housing, stacked flats, townhouses, and courtyard apartments.  When a preapproved middle housing plan is submitted for permit approval, the county or city's review of the preapproved plan may not be more than administrative. 

By July 1, 2025, fully planning counties and cities must:

• apply the same development permit and environmental review processes to multiplex housing that are applied to detached single-family residences;
• not impose or require zoning, development, siting, parking, design review, or other standards for multiplex housing that are more restrictive than those required for detached single-family residences, except when necessary for fire and life safety;
• not mandate setbacks for residential buildings or prohibit a residential building that is built to the property line within one-quarter mile of a community core location, except that such buildings may be required to adhere to fire code requirements; and
• not require more than a single stairway in a residential building of six or fewer stories if the building is located in a city with a municipal water supply and a professional fire department.

 
Residential infill development within one-quarter mile of a community core location is categorically exempt from SEPA.  A community core location is:  a stop on a high-capacity transportation system; commuter rail stops; stops on rail or fixed guideway systems; stops on bus rapid transit routes; stops for a bus or other transit mode providing actual fixed route service at intervals of at least fifteen minutes for at least five hours during the peak hours of operation on weekdays; public and private schools; and public parks.
 
The State Building Code Council (Council) must convene a work group to recommend additions or amendments to rules or codes that are necessary to apply the International Residential Code to multiplex housing and exempt multiplex housing from the International Building Code.  These recommendations must include those code changes necessary to ensure public health and safety in multifamily housing under the International Residential Code.  The work group must provide its recommendations and the Council must adopt or amend rules or codes in time for implementation in 2025.