General Regulations, Definitions, and Code Administration
Who may do what
Most administrations test first on authority. A licensed plumber may perform only work within the scope of the license; a permit is required before work begins and before anything is concealed; the code official may approve alternate materials, require tests, order corrections, and stop work. Learn the inspection sequence - rough-in before cover-up, final after fixtures are set and tested, plus specialty inspections for gas piping, water heaters, and backflow assemblies.
Definitions that decide answers
- Developed length - measured along the centerline of pipe and fittings, not the straight-line run.
- Fixture branch, fixture drain, branch, stack, building drain, building sewer - each has its own definition and its own sizing rule.
- Potable water, cross-connection, backflow, flood-level rim - definitions that carry into later domains.
Common traps
- Shall is mandatory; should is advisory. Questions are written around that distinction.
- Minor repair versus new work: stopping a leak or replacing fixture trim is usually exempt; new piping, new fixtures, and re-piping normally require a permit.
- Existing installations are not automatically legal - acceptance depends on whether the work was lawful when installed and whether it remains safe.
- An alternate material is not automatically rejected; it may be approved by the code official on demonstrated compliance.
Rule of thumb
If the work will be concealed, pressurized, or connected to a new fixture, assume a permit and an inspection are required unless the code expressly exempts it.
Worked example: A 40 ft straight run contains four 90° elbows. The developed length is not 40 ft - add the centerline length through each fitting from the manufacturer's data before sizing.