What minimum slope is required for a drainage pipe NPS 3 or smaller?
A drainage pipe of NPS 3 or less must have a downward slope of at least 1 in 50 in the direction of flow.
Conditions and exceptions
- Larger pipe sizes are permitted a shallower slope.
- Slope is measured in the direction of flow along the pipe run.
- Fixture unit loading and venting requirements apply independently.
Where this comes from
National Plumbing Code of Canada
This page states the requirement and points you to the publisher. It does not reproduce the code text — read the provision itself at the official source below.
Read the official text at NRC — Codes Canada publications →Verify this against the code edition actually adopted where you are building. Provinces, territories, and municipalities amend on their own schedules, and where the governing document and this page disagree, the governing document controls. This is not legal, engineering, or permitting advice. Last reviewed 2026-08-12.
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