This bill creates a new statutory category for "kit homes" and adds building-code provisions specific to them. It reenacts and amends RCW 19.27.015 to add and modify a set of definitions used in chapter 19.27 RCW and adds new sections to that chapter. The legal change is primarily a statutory and procedural change to the state building code framework: it defines a new type of residential structure (kit homes), requires rule making, and authorizes the State Building Code Council to update state building codes applicable to kit homes. This is not a criminal or penalty change. The bill defines "kit homes" as structures intended for residential use comprised of prefabricated walls, floors, and roofs assembled on-site and 800 square feet or smaller. Other definitions added or revised include agricultural structure, approval/approved/adopted, city, commercial building permit, emergency statewide amendment, model codes, model code organizations, multifamily residential building, off-cycle amendments, residential building permit, state building code, state building code adoption cycle, statewide amendment, and temporary growing structure. The State Building Code Council must perform rule making on codes applicable to kit homes no later than March 31, 2027, and is authorized to update the state building codes for kit homes. Cities and counties remain the issuers of commercial and residential building permits. The bill references RCW 19.27.015 (reenacted and amended), chapter 19.27 RCW (new sections), RCW 19.27.031, chapter 19.27A RCW, and RCW 34.05.350. Affected entities named in the bill include the State Building Code Council, cities and counties, model code organizations (examples listed), and the Washington State Legislature; the document also shows filing and passage records including Senate passage 1/21/2026 (49-0) and House passage 3/3/2026 (93-0). Important implementation details appear to be missing from the extracted text: the bill’s effective date, any budget or appropriation language, potential additional amendments elsewhere in chapter 19.27, and a clear approval or filing date. There are also inconsistent session/year labels in the header that are not explained in the provided material.

If enacted, the law will require the State Building Code Council to write and potentially change building code rules specifically for small prefabricated "kit homes" (defined as homes made of prefabricated walls, floors, and roofs assembled on site and 800 square feet or smaller) by March 31, 2027. That means the council will spend time and resources creating new or adjusted code language, and cities and counties that issue building permits will likely have to change permit review, inspection, and approval practices to apply whatever new rules the council adopts. The groups most directly affected are the State Building Code Council (new rulemaking work and authority to update codes), local permit offices (possible training, revised forms, and administrative workload), and manufacturers and buyers of kit homes (new compliance obligations and potentially different timelines or costs to get permits). The bill text does not include an effective date, budget or appropriation language, or other implementation details, so the size and timing of costs or staffing needs for agencies and local governments are unclear.