Seattle regulates plumbing work through two channels: plumbing permits (issued by the King County health authority for work inside the house) and side sewer permits (issued by the city for the drain line running to the main). Homeowners mostly need to know three things: which jobs trigger a permit, roughly what that costs, and why “the contractor said we don’t need one” is the most expensive sentence in home improvement.
Jobs that need a permit in Seattle
| Job | Permit needed? |
|---|---|
| Water heater replacement | Yes — plumbing permit |
| Repiping (any section of supply line) | Yes |
| Moving or adding fixtures (bath remodel, new bathroom) | Yes |
| Sewer or side sewer repair/replacement | Yes — side sewer permit |
| Tankless conversion | Yes (plumbing + often gas piping) |
| Replacing a faucet, toilet, or garbage disposal like-for-like | Generally no |
| Clearing a clog / drain cleaning | No |
| Repairing a leaking trap or supply stop | Generally no |
The pattern: like-for-like fixture swaps are fine; anything touching concealed piping, gas, the water heater, or the sewer needs paper.
What permits cost
Plumbing permit fees scale with fixture count — for typical residential jobs expect $100–$400. Side sewer permits and their inspections typically add $200–$600 to sewer work. On a multi-thousand-dollar job, permits are single-digit percentages; contractors who dodge them aren’t saving you money, they’re avoiding inspection of their own work.
The side sewer special case
Seattle requires side sewer work to be performed by a registered side sewer contractor and permitted before digging. Two homeowner-relevant consequences:
- The permit history of your side sewer is public. Before buying a pre-1960 Seattle house, checking whether the side sewer was ever replaced is a five-minute search that can save a five-figure surprise.
- Emergency repairs still get permitted — legitimate contractors handle it as part of the job, often same-day. A contractor proposing to “just fix it quietly” is transferring risk to you.
Why unpermitted work follows the house
Unpermitted plumbing surfaces at the worst times:
- Resale. Inspection findings of unpermitted water heaters or remodels become negotiating leverage against you, and some lenders balk.
- Insurance. A water-damage claim traced to unpermitted work gives your insurer an argument you don’t want them to have.
- Correction costs. Retroactive permitting can mean opening finished walls for inspection.
Outside Seattle?
Every wet-side jurisdiction runs its own flavor of this system — King County unincorporated areas, Bellevue, Tacoma, Everett, and Kitsap all permit water heaters and sewer work, with fees in similar ranges. The rule of thumb travels: concealed pipe, gas, water heaters, and sewers need permits everywhere; visible like-for-like swaps mostly don’t.
Hiring rule: a licensed contractor who pulls the permit and includes it as a line item is showing you their work will pass inspection. Treat “no permit needed” for any table-“Yes” job above as a disqualifier.