State plumbing guide · WA
Plumbing in Washington
Washington uses the Uniform Plumbing Code statewide and requires every plumber to be certified by the Department of Labor and Industries, including specialty certificates for residential service and backflow testing.
- Median home built
- 1987
- Built before 1980
- 42%
- Owner-occupied
- 63%
- Winter
- Regular hard freezes
- General statewide rating
- Plumbing code
- UPC
- City guides
- 3
Housing figures: U.S. Census Bureau, ACS 2024 1-year (B25035, B25034).
Washington city plumbing guides
How to check a plumber's license in Washington
Washington's Department of Labor and Industries certifies plumber trainees, journey-level plumbers, specialty plumbers and plumbing contractors; you must be certified to work in the plumbing trade. [1]
Which plumbing code applies in Washington
Washington adopts the 2021 Uniform Plumbing Code statewide, with state amendments, as chapter 51-56 WAC of the State Building Code. [2]
Seasonal problems to plan for in Washington
- Winter
- Hard freezes: protect exposed pipes, disconnect hoses. Frozen pipes.
- Storm season
- Heavy rain: sewer backups and sump pump failures.
How old Washington's homes are
Statewide, the median home was built in 1987 and 42% of homes predate 1980. Homes like that were usually built with copper or CPVC supply, plastic drains, and in some homes gray polybutylene supply pipe. The city guides below show how much that varies within the state.
Washington plumbing questions
How do I check a plumber's license in Washington?
Use L&I's Verify a Contractor, Tradesperson or Business tool to check both the plumbing contractor license and the individual plumber's certificate.
Which plumbing code applies in Washington?
The Uniform Plumbing Code (2021 edition) with Washington amendments, adopted statewide as chapter 51-56 WAC.
Sources (3)
- U.S. Census Bureau, ACS 2024 1-year (B25035, B25034) · checked 2026-10-01
- Washington State Department of Labor and Industries, Plumber Certification · checked 2026-10-01
- Washington State Building Code Council, Chapter 51-56 WAC (2021 UPC) · checked 2026-10-01