Do plumbing contractors need a license in Washington?
What the state requires, and what a hiring contractor will ask you for either way.
Yes. Plumbers are certified individually by L&I, in addition to the contractor registration the business holds.
This is different from Washington's general position, which is “registration required” for trades the state does not single out.
Last verified 2026-09-12 · Administered by Washington State Department of Labor & Industries
What Washington requires
What you will be asked for anyway
No state requirement does not mean no paperwork. Every hiring contractor and property manager worth working for asks for the same four things before anybody starts, and asks again every time one expires.
- 1
Certificate of insuranceGeneral liability, naming them as additional insured.
- 2
Surety bondOften required by cities that register your trade, and by plenty of hiring contractors regardless.
- 3
Signed subcontractor agreementTheirs, not yours. Scope, payment terms, and who carries what.
- 4
W-9So they can 1099 you. It carries your TIN, so it is the one to be careful with.
Your compliance pack, sent in one link.
Keep them in one place and answer the next contractor who asks in about six seconds — with a page showing your carrier, policy number, cover and expiry, that updates itself when you renew. Free, and whoever you send it to needs no account.
Set up your compliance packCheck the certificate before they start.
A plumbing license in Washington can be looked up, and should be. What you can always check is the insurance, the bond, and whether either has lapsed since the day it was emailed to you. That last part is where it usually goes wrong: a PDF attached in March says nothing about July.
Keep a roster current