(1) The legislature finds that lowering the cost of middle and multiplex housing construction will increase the housing supply and help address the state's shortage of affordable housing. It further finds that home builders and residentially focused architects are more familiar with the provisions of the international residential code. Allowing middle and multiplex housing to be built according to the standards of the international residential code will result in housing being easier to build and more affordable without sacrificing quality and safety. Therefore, the legislature intends to simplify the production of middle and multiplex housing by allowing more types of housing to use provisions of the international residential code.

(2) The state building code council shall convene a technical advisory group for the purpose of recommending the additions or amendments to rules or codes that are necessary for the council to apply the Washington state residential code to multiplex housing. The technical advisory group shall determine the most efficient mechanism to implement these changes in the Washington state residential code. These recommendations must include those code changes necessary to ensure public health and safety in multifamily housing under the international residential code and must consider the life safety systems and accessibility requirements for multiplex housing from the Washington state building code.

(3) The advisory group shall provide its recommendations to the council in time for the council to adopt or amend rules or codes as necessary for implementation in the 2024 international building code. The council shall take action to adopt additions and amendments to rules or codes as necessary to apply the international residential code to multiplex housing by November 1, 2026.

(4) For the purposes of this section, "multiplex housing" means a building with up to six dwelling units consolidated into a single structure with common walls and floors and a functional primary street entrance, or a building of up to three stories containing up to six dwelling units consolidated into a single structure.