Washington plumbing: certificates, owner work and helpers

Source: Local Help Stations (localhelpstations.com). Last updated November 2, 2026.

Washington plumbing rules here come from RCW 18.106 and the Labor and Industries plumber certification program.

What Washington rules say

Plumbing for others requires a state certificate, such as journey level, specialty, residential service, temporary permit or trainee. (source: Washington State Legislature)
Only plumbers certified by Labor and Industries may legally do plumbing on property they do not own. (source: Washington State Department of Labor and Industries)
Since 2021, a contractor that sends people to do plumbing must itself be a licensed plumbing contractor. (source: Washington State Legislature)
Each day of unlicensed plumbing work, bidding or advertising counts as a separate infraction. (source: Washington State Legislature)
You do not need a license to do plumbing at your own home, farm or business. (source: Washington State Legislature)
A householder may also get help from a friend, neighbor or relative. (source: Washington State Legislature)
A residential service plumber may repair or replace existing fixtures and piping in single family homes and duplexes. (source: Washington State Legislature)
Labor and Industries makes random jobsite checks to see that certified plumbers do the work and supervise trainees. (source: Washington State Department of Labor and Industries)

This page covers statewide rules only. Cities and counties can add their own permits and licenses, so check with your local building office too.

Last updated: November 2, 2026