Summary: Factory-assembled structures include both residential and commercial structures that are built off-site in a factory and are later transported to a building site for installation. The State Department of Labor and Industries (L&I) regulates and approves the construction of all factory-assembled structures that are sold, leased or used in Washington state. Site installation requirements and inspections vary with the type and use of the factory-assembled structure and are generally the responsibility of the local jurisdiction where the structure is to be located. This Tip describes the types of factory-assembled structures allowed in Seattle, along with their permitting and inspection requirements.
Date Revised: 02/28/2023