DE Plumber cheat sheet

Fixture unit (FU): a drainage fixture unit approximates 1 cubic foot per minute (about 7.5 gpm) of flow; supply fixture units are converted to probable demand using Hunter's curve, not simple addition.

Slope rules: 2-inch and smaller drain pipe at 1/4 inch per foot; 3-inch and larger at 1/8 inch per foot minimum; 4-inch and larger may use 1/8 inch per foot where the code allows.

Water column pressure: 1 psi = 2.31 feet of head. Static pressure at a fixture = supply pressure minus 0.433 psi per foot of elevation rise.

Developed length includes all pipe plus equivalent lengths for fittings (commonly 5 ft per 90-degree elbow, 2 ft per 45-degree elbow for sizing estimates).

A trap seal is 2 to 4 inches deep; the trap weir is the invert of the trap outlet, and the vent must connect within the trap arm distance limits (e.g., 5 ft for 1-1/4 inch, 6 ft for 1-1/2 inch, 8 ft for 2 inch).

Air gap: the unobstructed vertical distance between the supply outlet and the flood-level rim must be at least twice the effective opening diameter, never less than 1 inch.

Water heater temperature and pressure relief valve discharge must terminate by gravity, with the pipe not reduced and not trapped, ending 6 to 24 inches above the floor or outside.

Backflow prevention hierarchy: air gap > reduced pressure zone assembly > double check valve; devices must be tested and tagged per local requirements.

Water supply sizing uses velocity limits: keep cold water under about 8 fps and hot water under about 5 fps to control noise and erosion-corrosion.

Codes are adopted locally: the model code (Uniform Plumbing Code or International Plumbing Code) applies only as amended by the jurisdiction; always confirm the adopted edition and local amendments.

Permits are typically required for new construction, additions, alterations, and replacement of water heaters, sewers, and water services; ordinary repairs like faucet washers may be exempt.

A plumbing inspector must be notified for required inspections: rough-in (before covering), water test, drain/waste/vent test, gas piping test, and final inspection.

Drainage and vent systems require a water or air test: commonly a 10-foot head of water for 15 minutes on DWV, and air test at 5 psi for 15 minutes where allowed.

Vent termination: stack vents and vent stacks must extend at least 6 inches above the roof, or higher where snow or adjacent openings require; vents must be at least 10 feet from or 2 feet above windows and air intakes.

Cleanouts: required at the base of each stack, at changes of direction greater than 135 degrees, and at intervals not exceeding 100 feet in horizontal building drains.

Licensing is separate from code compliance: a journeyman or master license is required to perform or supervise plumbing work, and a contractor license or bond is required to contract for it.

Gas piping sizing follows the longest-run method; the code tables give capacity by pipe size, length, and specific gravity, and pressure testing is typically 10 psi for 30 minutes on systems above 14 inches water column.

Confined spaces (vaults, pits, sewers): test the atmosphere for oxygen, combustible gas, and hydrogen sulfide before entry; oxygen-deficient atmospheres are below 19.5 percent oxygen.

Hydrogen sulfide is heavier than air and deadens the sense of smell at higher concentrations; never rely on odor as a warning, and use supplied-air or SCBA where required.

Lead and asbestos: pre-1978 housing and pre-1986 solder may contain lead; asbestos may be in pipe insulation and older cement products. Follow applicable abatement and notification rules.

Trench safety: excavations 5 feet or deeper require a protective system (sloping, shoring, or shielding) unless in stable rock; a competent person must inspect daily and after rain.

Ladder and fall safety: maintain three points of contact, set ladders at about a 4:1 angle, and use fall protection when working 6 feet or more above a lower level in general industry.

Soldering and brazing hazards: keep a fire watch and a suitable extinguisher, purge and ventilate lines, and never use oxygen as a substitute for compressed air to test or blow lines.

Backflow and cross-connection control protects potable water; also protect workers from sewer gas, biological hazards, and contaminated water during repairs with PPE and disinfection.

Lockout/tagout: isolate and verify zero energy on pumps, heaters, and electrical circuits before service; treat all circuits as energized until tested.

Bid price = direct costs (labor, material, equipment, subcontractors) + indirect/overhead + markup for profit and contingency; a common formula is price = cost / (1 - desired margin).

Labor hours estimate = quantity / production rate; use historical production rates (e.g., hours per fixture or per foot of pipe) rather than guesses.

Change orders must be documented in writing with scope, price, and schedule impact before work proceeds; undocumented extras are commonly uncollectible.

Retainage is typically 5 to 10 percent withheld until substantial completion; cash flow planning must account for retainage and payment lag.

Contract types: lump sum (fixed price), time and materials (cost plus), and unit price. Each shifts risk differently between owner and contractor.

Schedule critical path: identify the longest dependent chain of tasks; float is the slack on non-critical tasks, and delays to critical-path tasks delay completion.

Warranty and lien basics: retain lien rights by serving preliminary notices and filing within statutory deadlines; keep as-built records and warranty documents for the owner.

Job costing compares estimated versus actual labor and material by phase; variance analysis drives corrective action and future bid accuracy.