Plumbing Discipline - SCO Plumbing & Gas
The Plumbing Discipline domain tests the Safety Codes Officer's ability to apply the National Plumbing Code of Canada and the administrative framework of the Safety Codes Act during permit review, inspection, and enforcement. Questions focus on drainage and venting, water supply, fixtures, backflow prevention, materials, testing, and documentation. You are expected to read a described installation, identify the governing code requirement, and decide whether to approve it, reject it, or order a correction.
Drainage, venting, and water supply
- Drainage pipe slope is 2% (1 in 50) for 3 in and smaller, and 1% (1 in 100) for 4 in and larger. The slope must be continuous in the direction of flow.
- Each fixture trap must be vented. Trap arm length is limited by trap size to prevent self-siphonage; a 1-1/2 in trap arm is commonly limited to 1.8 m (6 ft), and a 2 in trap arm to 2.4 m (8 ft).
- Trap seals are typically 50–100 mm (2–4 in) deep and must be protected from siphonage, back pressure, and evaporation.
- Vent terminals must be outside, above the roof, and clear of windows, doors, and air intakes. Air admittance valves are restricted to specific locations and do not replace a vent everywhere.
- Water supply must be sized for fixture demand and pressure. Every cross-connection needs an approved backflow preventer, including hose bibs, boiler fills, irrigation, and chemical dispensers.
- Drainage, waste, and vent systems are tested with water or air; water supply is pressure-tested before concealment.
Worked example
A plan shows a 1-1/2 in lavatory trap arm running 2.1 m (7 ft) from the trap weir to the vent connection at 1/4 in per foot slope. The installer argues the slope is correct. The SCO rejects the installation. Slope is not the issue; trap arm length is. For a 1-1/2 in trap, the limit is 1.8 m (6 ft). At 2.1 m the trap arm can self-siphon when the fixture drains, breaking the trap seal. The correction is to relocate the vent closer to the trap or redesign the branch only where the code permits a larger trap arm with a corresponding trap size increase. The SCO records the measured length and cites the trap arm limit.
Traps that cost marks
- Applying the 1% slope to a 3 in drain; the 1% allowance starts at 4 in.
- Approving a trap arm because the slope looks right while ignoring the length limit.
- Missing backflow protection on a minor-looking connection such as a hose bib or boiler fill.
- Treating an air admittance valve as equivalent to a vent in every location.
- Signing off without verifying test pressure, duration, and concealment.