All persons throughout the state working at the business of interior plumbing must be licensed plumbers or registered apprentices. No person, firm, or corporation shall engage in the business of planning and installing plumbing, nor install plumbing in connection with the dealing in and selling of plumbing material and supplies unless at all times a licensed master plumber or restricted master plumber, who shall be responsible for proper installation, is in charge of the plumbing work of the person, firm, or corporation.
A licensed master or journeyman plumber may perform plumbing anywhere in Minnesota. Those with restricted licenses may perform plumbing in the state in cities with a population of fewer than 5,000.
Persons having certification as pipelayers may only perform sewer and water services installation outside of buildings, if properly bonded.
All plumbing plans, including site utilities, submitted to DLI for projects located in cities with a population more than 5,000, must be signed by a master plumber or a professional engineer that is registered in Minnesota. Plumbing plans, including site utilities, in cities that have a population of less than 5,000 must be signed by a master plumber, a restricted master plumber, or a professional engineer that is registered Minnesota.
When a master or restricted master plumber designs the plumbing plans, only the individual who has prepared the plans may use the plans for construction. If another plumber is contracted to install the plumbing, they must submit their own plans and specifications for the project.