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 (IBC), the International Residential Code (IRC), and the Energy Code.

The IBC establishes minimum requirements for all buildings except detached one- and two-family dwellings and townhouses up to three stories.  The IRC 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.

The IBC currently requires dwelling units to have a minimum of 190 square feet of habitable space and at least one room with no less than 120 square feet of net floor area. 

National Healthy Housing Standard.
The National Healthy Housing Standard is published by the National Center for Healthy Housing and the American Public Health Association.  The standard recommends minimum performance requirements for housing including:  duties of owners and occupants; structure, facilities, plumbing, and space requirements; safety and personal security; lighting and electrical systems; thermal comfort, ventilation, and energy efficiency; moisture control, solid waste, and pest management; and chemical and radiological agents.  The standard recommends that each dwelling unit provide privacy and adequate space for sleeping and living and that every habitable room have a minimum floor area of 70 square feet. 

Passive House.
Passive house is a voluntary standard for energy efficiency in buildings, which typically requires little energy for heating or cooling.  Certified passive house projects currently meet the requirements of the State Energy Code.  

Development Regulations.
The Growth Management Act (GMA) is the comprehensive land use planning framework for counties and cities in Washington.  Currently, 28 counties, and the cities within those counties, fully plan under the GMA.  The GMA directs fully planning counties and cities to adopt internally consistent, comprehensive land use plans.  Comprehensive plans must be reviewed and, if necessary, revised every 10 years.  Fully planning counties and cities also must adopt development regulations to implement their comprehensive plans.  Development regulations include a variety of land use regulations, including zoning and subdivision ordinances, environmental procedures, design review and off-street parking requirements, and bulk, density coverage, and setback limitations.  

Limitations on Off-Street Parking Requirements.
The GMA contains limitations on the ability of fully planning counties and cities to establish minimum residential parking requirements for certain types of housing, including:

• For market rate multifamily housing units located within 0.25 miles of a transit stop that receives frequent transit service, no more than one parking space per bedroom or 0.75 of a parking space per unit may be required.
• For housing units designed for seniors and people with disabilities located within 0.25 miles of a major transit stop, no minimum residential parking limitations may be imposed.
• For accessory dwelling units (ADUs) located within 0.5 miles of a major transit stop, no minimum residential parking requirements may be imposed.  For all other ADUs, no more than one or two off-street parking spaces may be required, depending on the size of the lot.
• For middle housing located within 0.5 miles of a major transit stop, no minimum residential parking requirements may be imposed.  For all other middle housing, no more than one or two off-street parking spaces may be required, depending on the size of the lot.

State Building Code.
The Council must convene two technical advisory groups to recommend changes to the Code.  The first advisory group must recommend additions or amendments to rules or codes that are necessary to apply the IRC to multiplex housing and exempt multiplex housing from the IBC.  The recommendations must include those code changes necessary to ensure public health and safety in multifamily housing under the IRC and may include life safety systems for multiplex housing in the IBC. 

The second technical advisory group must recommend amendments to the IBC that would allow for a minimum dwelling unit size less than 190 square feet but at least 70 square feet.  The advisory group must strive to align the Code sections related to interior environment with the relevant sections of the National Healthy Housing Standard.  When developing the recommendations, the advisory group must review the differences between the Code and the National Healthy Housing Standard in consultation with experts in public health and fire safety.

Both technical advisory groups must provide their recommendations to the Council in time for the Council to adopt or amend rules or codes as necessary for implementation in the 2024 IBC.  The Council must take action to adopt additions and amendments to rules or codes as necessary by July 1, 2026. 

The Office of Regulatory Innovation and Assistance (ORIA) must contract with a qualified external consultant or entity to develop a standard plan set demonstrating a prescriptive compliance pathway that will meet or exceed all energy code regulations for residential housing subject to the IRC.  The standard plan set may be used by local governments and building industries.  In developing the standard plan set, the consultant must seek feedback from cities, counties, building industries, and building officials. The standard plan set must be completed by June 30, 2025.

Development Regulations.
For retrofits of existing buildings to be used for residential housing, a city or county must allow the portion of exterior wall assemblies that include insulation to project up to an additional eight inches into the setbacks on all sides.  If a nonconforming building already projects into setbacks, a city or county must allow the portion of exterior wall assemblies that include insulation to project up to an additional 8 inches into the setbacks on all sides if the building is to be used for residential housing. 

For retrofits of existing buildings to be used for residential housing, gross floor area must be measured from the interior face of the exterior walls, which includes drywall, as typically depicted on the architectural floor plans.

Passive House.
For new residential construction meeting passive house requirements:

1. any required setback must be measured to the outside face of the foundation, and a city or county must allow the portion of exterior wall assemblies that include insulation to project up to 8 inches into setbacks on all sides; and
2. gross floor area must be measured from the interior face of the exterior walls, which includes drywall, as typically depicted on the architectural floor plans.

For new construction and the retrofit of existing buildings meeting passive house requirements, a city or county must allow residential housing to exceed the maximum allowable roof height by 8 inches to accommodate additional insulation.

Limitations on Off-Street Parking Requirements.
A city or county may not require off-street parking as a condition of permitting a residential project meeting passive house requirements.

A city or county may not require off-street parking as a condition of permitting a residential project if compliance with tree retention or protection requirements would otherwise make a proposed residential development or redevelopment infeasible.