What building sewer means
The building sewer is the pipe that runs from the end of the building drain outside the house to the public sewer or the septic tank.
Also called sewer lateral, sewer line.
Where it matters on a plumbing job
Root intrusion and bellies in old clay or cast iron sewers are steady work. Who owns which part of the lateral differs by city, so check before you quote digging near the street.
What the model code says
- The code defines the building sewer as the part of the drainage system that runs from the building drain to a public sewer, private sewer or septic system. (IRC 2021, Chapter 2)
Check which code edition your building department enforces for building sewer before you quote.
What it costs
Jobs that involve building sewer are priced in the sewer line replacement cost guide: about $3,300 typical, usually $1,400 to $5,300. The guide shows its sources and what moves the price.
Work it out
- Cost guide: Sewer line replacement cost
- Licensing: Plumbing license rules by state
- Tools, templates and guides: Free plumbing resources
Sources: 2021 International Residential Code, Chapter 2, Definitions (ICC). Checked October 9, 2026.