The bill aims to enhance the construction of middle and multiplex housing in Washington State by allowing these types of housing to adhere to the standards of the international residential code. It establishes a technical advisory group under the state building code council to recommend necessary amendments to the Washington state residential code, ensuring that public health and safety standards are maintained. The advisory group is tasked with providing recommendations by a specified timeline to facilitate the adoption of these changes by November 1, 2026. The bill defines multiplex housing as buildings with up to six dwelling units and outlines the council's responsibilities in implementing these changes.

Additionally, the bill mandates the formation of another technical advisory group to recommend amendments to the international building code, specifically regarding minimum dwelling unit sizes that may be smaller than current efficiency dwelling unit requirements. This group will also align state building code sections with the national healthy housing standard and will incorporate feedback from public health and fire safety experts. Furthermore, the office of regulatory innovation and assistance is directed to contract with an external consultant to develop a standard energy code plan set for residential housing, which must be completed by June 30, 2025.