General Building and Plumbing Code Requirements, Definitions, and Standards
Definitions Decide the Answer
Many items on the exam are vocabulary problems in disguise. You must be fluent with: fixture (a receptor that receives water or waste), fixture unit (a drainage-load measure, not a flow rate), trap seal (the water barrier in a trap, commonly 2 to 4 inches deep), developed length (measured along the centerline of pipe and fittings), stack, branch, vent, backflow, and potable water. Two terms are commonly confused: a common vent serves two traps, while a wet vent is a drain that also serves as a vent for other fixtures.
Referenced Standards
Codes rarely spell out product properties; they reference standards. Plumbing fixtures are listed to ASME/CSA fixture standards, pipe and fittings to ASTM or AWWA standards, and materials in contact with drinking water to NSF/ANSI 61 plus lead-free requirements. A product that is not listed and labeled for the use fails, no matter how long it has been installed that way.
Traps in Questions
- Mixing drainage fixture units (DFU) with water supply fixture units (WSFU): drainage sizing uses DFU, supply sizing converts WSFU to gallons per minute.
- Forgetting that developed length includes fittings, so it is always longer than the tape measure run.
- Assuming code minimums are the maximum allowed; a job specification or contract may be stricter than code.
- Ignoring that the more restrictive requirement governs when two rules overlap.
Rule of Thumb
Slope: 1/4 inch per foot for 2-1/2 inch and smaller pipe, 1/8 inch per foot for 3 inch through 6 inch pipe. Convert to percent by multiplying inches per foot by 100/12, so 1/4 inch per foot is about 2.1 percent.