OBC Plumbing House cheat sheet

Fixture unit (fU): a dimensionless measure of the probable load a fixture places on the drainage or water supply system; 1 fU equals roughly 1 cubic foot per minute (7.5 gpm) of flow.

Drainage fixture unit (DFU) rates fixture discharge into a building drain; supply fixture unit (WSFU) rates demand on the water distribution system, and the two scales are not interchangeable.

Slope is vertical fall per unit horizontal run: 1/4 inch per foot equals 2.08 percent; 1/8 inch per foot equals 1.04 percent; 1/2 inch per foot equals 4.17 percent.

A trap seal is the water depth in a trap, commonly 2 to 4 inches; a trap weir is the top edge of the trap dip that sets the seal depth.

Vent stack versus stack vent: a stack vent is the extension of a soil or waste stack above the highest fixture branch; a vent stack serves lower fixtures only.

A wet vent is a vent that also carries waste from fixtures on the same floor; a dry vent carries air only.

Plan symbols: solid line = drain below floor or concealed; dashed line = vent; circle with cross = floor drain; triangle = cleanout.

Developed length is the total measured run of pipe along its centerline including fittings; it governs trap arm length and vent distance limits.

A plumbing permit is required before installing, altering, or replacing any plumbing system or fixture, except minor repairs such as clearing stoppages or replacing washers.

Permits are issued to the owner or a licensed contractor; the permit must be posted on the job site and available for inspection.

Required inspection sequence: rough-in (before concealing), then final; some jurisdictions add a slab or underground inspection before the slab is poured.

Concealed work must be tested and approved before covering; a water test of the DWV system typically holds 10 feet of head (about 4.3 psi) for at least 15 minutes.

Final inspection verifies fixtures are set, traps primed, vents terminate properly, and all fixtures have potable water and function.

Work done without a permit is subject to stop-work orders, double fees, or removal and re-inspection at the owner's expense.

A certificate of occupancy may be withheld until plumbing final approval is granted by the authority having jurisdiction (AHJ).

Inspections must be requested within the time the AHJ specifies; work covered before inspection may be ordered exposed.

Building drain carries waste to the building sewer; it extends 30 inches outside the building wall, where it becomes the building sewer.

Fixture branch diameter is set by the largest DFU load served; a water closet requires a minimum 3-inch branch.

Trap arm length limits: 1-1/4 inch trap = 5 feet, 1-1/2 inch = 6 feet, 2 inch = 8 feet, 3 inch = 12 feet, 4 inch = 16 feet, measured from trap weir to vent.

Every trap must be vented, and each trap arm may serve only one fixture (except where a common vent or wet vent is permitted).

Vent terminals must extend at least 6 inches above the roof and be at least 10 feet from or 2 feet above any window, door, or air intake.

Cleanouts are required at the base of each stack, at the building drain, at changes of direction over 45 degrees, and at intervals not exceeding 100 feet on horizontal runs.

Horizontal drainage pipe must slope at least 1/4 inch per foot for pipe 3 inches and smaller, and 1/8 inch per foot for 4 inches and larger.

A backwater valve is required on fixtures below the level of the next upstream manhole to prevent sewage backup.

Static pressure at fixtures should be between 40 and 80 psi; above 80 psi a pressure-reducing valve is required, and below 20 psi may indicate inadequate supply.

Thermal expansion of heated water in a closed system requires an expansion tank or thermal expansion relief device.

Water heater temperature and pressure relief (TPR) valve discharge must terminate 6 to 24 inches above the floor or outside, never capped.

Minimum pipe sizing uses the WSFU method or the fixture-count method; a 3/4-inch service line commonly serves a single-family dwelling.

Backflow prevention: an air gap is the highest protection; a reduced-pressure-zone (RPZ) assembly is required for high-hazard cross-connections.

Shock arrestors absorb water hammer from fast-closing valves and are installed near the fixture or valve.

Water service line depth must be below the local frost line to prevent freezing; typical minimum cover is 12 to 48 inches depending on climate.

Hot water distribution: recirculation or a manifold system reduces wait time; hot and cold lines should be insulated to limit heat loss.

Water closets must use no more than 1.6 gallons per flush (gpf); high-efficiency models use 1.28 gpf or less.

Urinals are limited to 1.0 gpf, and high-efficiency urinals to 0.5 gpf or less.

Showerheads are limited to 2.5 gpm at 80 psi; lavatory faucets are limited to 2.2 gpm, and kitchen faucets to 2.2 gpm.

A fixture must be set level and securely fastened; floor-mounted water closets require a closet flange at finished floor level.

Each fixture must have a trap with a water seal of 2 to 4 inches, and no fixture may be double-trapped.

Fixture clearances: a water closet needs at least 15 inches from centerline to any side wall and 21 inches in front.

Drinking fountains must be provided where required by occupancy, and each must have an accessible height and knee clearance.

Garbage disposals must be connected to a drain with a trap; a dishwasher must have an air gap or high loop for backflow protection.

Storm drainage is separate from sanitary drainage; combined systems are prohibited in most modern jurisdictions.

Roof drains are sized using the 100-year, one-hour rainfall intensity for the site, plus the roof area served.

Primary and secondary (overflow) roof drainage: secondary drains or scuppers must handle the design storm if the primary is blocked.

A trap is required on each roof drain or area drain to prevent sewer gas escape, and it must be protected from freezing.

Special wastes include grease, oil, sand, and chemical wastes; a grease interceptor is required for food service and must be sized to the fixture load.

Grease interceptors must be installed outside the building, with a minimum 2-inch inlet and outlet and access for cleaning.

Acid-neutralizing sumps are required for laboratory or plating wastes that discharge corrosive liquids.

Sump pumps discharge to an approved point; check valves prevent backflow and a dedicated circuit supplies power.

Copper tube types: K (thickest, underground), L (standard above ground), M (thin wall, above ground only).

PEX is joined with crimp or expansion fittings; it must be protected from UV light and from physical damage.

PVC DWV uses solvent cement; primer is required before cement on PVC, and joints must be fully inserted and twisted a quarter turn.

Cast iron soil pipe joins with no-hub couplings or hub-and-spigot lead joints; no-hub couplings require a torque wrench to the manufacturer's spec.

Galvanized steel pipe is joined with threaded fittings; dielectric unions are required where steel meets copper to prevent galvanic corrosion.

ABS pipe uses ABS solvent cement; PVC and ABS cement are not interchangeable.

Brass and bronze fittings are used for valves and trim; lead-free solder is required for potable water joints.

Support spacing: copper horizontal runs about every 6 feet, PVC about every 4 feet, and cast iron every 5 feet with hangers near joints.

A fire sprinkler system is a separate piping system with its own water supply and backflow prevention; it must not be connected to the domestic system without an approved backflow device.

Sprinkler head spacing: standard spray heads cover up to 130 square feet for light hazard, and heads must be at least 6 inches below the ceiling.

A standpipe system delivers water to fire hose connections in tall or large buildings; class I serves firefighters, class II serves occupants, class III serves both.

Fire department connections (FDC) must be accessible, marked, and located within the required distance of a hydrant.

A fire pump boosts pressure when the public supply is inadequate; it requires a dedicated suction line and a test header.

Specialty systems include medical gas (oxygen, vacuum), which requires brazed joints, dedicated piping, and certified installers.

A backflow preventer on the fire line must be inspected and tested annually per the AHJ.

Flow test data (static, residual, and pitot pressure) determine the available fire flow at a site.

Potable water must be protected from contamination by an air gap of at least twice the effective diameter of the supply pipe, and never less than 1 inch.

Cross-connections are prohibited; any connection between potable and non-potable water must have an approved backflow preventer.

Sewer gas contains methane and hydrogen sulfide; traps and vents keep gas out of occupied spaces.

Plumbing fixtures must be smooth, nonabsorbent, and easily cleanable; food service areas require indirect waste connections.

Indirect waste piping discharges through an air gap into a receptor; the gap must be at least 1 inch or twice the pipe diameter.

Water heaters must be seismically strapped where required and have a TPR valve piped to a safe discharge point.

Confined-space entry for sewer work requires gas testing and ventilation; hydrogen sulfide is heavier than air and collects in low areas.

Handwashing sinks must be provided in food preparation and toilet room areas; each must have hot and cold water, soap, and towels.

Plumbing penetrations through fire-rated assemblies must be firestopped with an approved listed system equal to the rating of the assembly.

Structural members may not be notched or bored beyond code limits; a bored hole in a 2x10 joist must stay within the middle third of the depth and no larger than one-third the depth.

Pipe sleeves are required where piping passes through concrete or masonry, and the annular space must be sealed.

Electrical coordination: a dedicated GFCI circuit is required for receptacles near sinks and for pumps in wet locations.

HVAC coordination: condensate drains must connect to an approved receptor with an air gap, not directly to the sanitary drain.

Plumbing must maintain required clearances from electrical panels and gas meters and from storage water heaters' combustion air openings.

Access panels are required for concealed valves, cleanouts, and fixtures that need service.

The plumbing code and building code are adopted together; where they conflict, the more restrictive requirement governs.