(1) Nothing in this chapter shall be construed to require that a person obtain a license in order to do plumbing work at his or her residence or farm or place of business or on other property owned by him or her.
(2) A current certificate of competency or apprentice permit is not required for:
(a) Persons performing plumbing work on a farm; or
(b) Certified journey level electricians, certified residential specialty electricians, or electrical trainees working for an electrical contractor and performing exempt work under:
(ii) After January 1, 2021, under subsection (8) of this section.
(3) Nothing in this chapter shall be intended to derogate from or dispense with the requirements of any valid plumbing code enacted by a political subdivision of the state, except that no code shall require the holder of a certificate of competency to demonstrate any additional proof of competency or obtain any other license or pay any fee in order to engage in the trade of plumbing.
(4) This chapter shall not apply to common carriers subject to Part I of the Interstate Commerce Act, nor to their officers and employees.
(5) Nothing in this chapter shall be construed to apply to any farm, business, industrial plant, or corporation doing plumbing work on premises it owns or operates.
(6) Nothing in this chapter shall be construed to restrict the right of any householder to assist or receive assistance from a friend, neighbor, relative, or other person when none of the individuals doing such plumbing hold themselves out as engaged in the trade or business of plumbing.
(7) This section does not apply to anyone installing, altering, repairing, or renovating medical gas systems.
(8) As of January 1, 2021, nothing in this chapter shall be construed to apply to an entity who holds a valid electrical contractor's license under chapter
19.28 RCW that employs a certified journey level electrician, a certified residential specialty electrician, or an electrical trainee meeting the requirements of chapter
19.28 RCW to perform plumbing work that is incidentally, directly, and immediately appropriate to the like-in-kind replacement of a household appliance or other small household utilization equipment that requires limited electrical power and limited waste, water connections, or both. An electrical trainee must be supervised by a certified electrician while performing plumbing work.