What sewer pipe does my Seattle house probably have, by the year it was built?

Why the year matters

Sewer pipe was chosen by what was available and affordable in the year the trench was open, so the build date is a strong first guess at what is underground. It sets expectations for how the pipe fails, whether it can be lined, and how urgent an inspection is. It does not replace a camera — plenty of 1910 houses have a 1998 side sewer — but it tells you what to look for.

Decade by decade

Where each era sits on the map

• Pre-1920 and 1920s: Capitol Hill, Queen Anne, Wallingford, Fremont, Ballard, Beacon Hill, Ravenna, Green Lake, the older streets of West Seattle.
• 1930s–40s: Laurelhurst, Windermere, Magnolia, north Ballard.
• Postwar (1945–65): Lake City, Shoreline, Edmonds, Lynnwood, Mountlake Terrace, early Bellevue and Kirkland.
• 1965–85: Bothell, Kenmore, Redmond, much of Bellevue and Everett's suburbs.

Reading the table

The dates are transitions, not switches. Builders used up stock, plumbers had habits, and a house finished in 1974 may have any of three materials in the yard. The building drain column matters as much as the side sewer column: the cast iron under a 1950s slab is now as old as the concrete outside it and fails in its own way, which the under-slab vs. side sewer article covers. And "typical issues now" is what we see on camera in that era of house today, not what is inevitable — a well-bedded clay line under a lot with no big trees can be in remarkable shape at a hundred years old.

Mixed lines are the norm

A very common Seattle profile: original cast iron under the slab, a 1990s PVC section near the house where a previous owner fixed a collapse, and original clay from there to the main. Each section has its own condition and its own best fix, and a bid that treats the whole run as one thing is guessing. This is the practical reason to insist on a full-length camera inspection with distances noted, rather than a look at the first twenty feet.

What to do with the guess

1. Look up the build year on the King County parcel viewer.
2. If it is before 1975 and the line has never been inspected, get a camera in it — especially before buying, selling, adding a unit, or paving over the route.
3. Ask the inspector to name the material in each section and note where it changes.
4. Match the material to the options: joint problems in clay or concrete lean toward lining; Orangeburg and collapsed sections lean toward replacement, usually by bursting.