SCO Plumbing & Gas cheat sheet

Fixture unit method: 1 FU equals 1 cubic foot per minute of drainage flow; convert total fixture units to litres per second using the sizing tables in the applicable plumbing code, then select pipe diameter from slope and FU load.

Minimum drain pipe slope is 1 in 50 (2%) for pipes 75 mm and smaller and 1 in 100 (1%) for pipes 100 mm and larger unless the adopted code states otherwise; flatter grades risk solids deposition.

Soil stack sizing must account for both fixture units per stack and total stack height; a stack serving more than 10 storeys requires special venting design and engineered sizing.

Vent sizing rule: the vent must be at least half the diameter of the drain it serves and never smaller than 32 mm; a 100 mm drain requires a minimum 50 mm vent.

Trap seal depth is 50 mm to 100 mm; each fixture trap must be protected from siphonage by a vent within the prescribed distance (commonly 1.5 m developed length for 40 mm traps).

Water supply sizing: use the fixture unit demand method with the Hunter curve or the code's loading table, then check residual pressure at the most remote fixture; minimum residual is typically 100 kPa for flush tanks and 150 kPa for flush valves.

Backflow protection hierarchy: air gap is the highest protection, followed by reduced pressure zone assembly, then double check valve assembly, then vacuum breaker; select based on hazard level and whether the risk is backpressure or backsiphonage.

Pressure testing: water supply systems are tested at 1.5 times working pressure but not less than 1000 kPa for at least 2 hours with no drop; drainage systems are tested with a 3 m head of water or 50 kPa air test where permitted.

Gas pipe sizing by the longest-run method: measure the developed length from the meter to the most remote appliance, sum the connected load in MJ/h, then read the capacity table for that length and allowable pressure drop.

Natural gas heat content is approximately 37 to 38 MJ/m3 at standard conditions; propane is approximately 93 MJ/m3 as vapour, so conversion between fuels requires recalculating the load, not just the pipe size.

Specific gravity affects capacity: natural gas is about 0.60 relative to air, propane vapour about 1.53; heavier-than-air gases settle in low points and require different ventilation and leak detection practice.

Pressure drop allowance: typical low-pressure systems allow 0.125 kPa (about 0.5 in water column) total drop from meter to appliance; medium-pressure systems allow a larger drop but require a regulator at each appliance.

Combustion air: an appliance needs approximately 1 m3 of air per 1 MJ of input for complete combustion plus dilution; confined spaces require two permanent openings sized per the code, one near the top and one near the bottom.

Flue and vent rules: a natural draught flue must rise at least 1.5 m above the draught hood and terminate above the roof line; the termination must clear windows, doors, and air intakes by the code minimum distances.

Leak testing: new gas piping is pressure tested with air or inert gas at 1.5 times the maximum operating pressure but not less than 7 kPa for low-pressure systems, held for a defined period with no loss on a gauge.

Gas detector placement follows gas density: mount methane detectors near the ceiling or at high-level returns, and propane detectors near floor level, within the appliance room and at the likely leak source.

Fixture unit values are assigned by fixture type: a water closet with flush tank is 4 FU, a flush valve water closet is 6 FU, a lavatory is 1 FU, a bathtub is 2 FU, and a floor drain is 1 FU for drainage sizing.

Developed length includes all fittings as equivalent pipe length: add roughly 0.6 m per 90-degree elbow and 0.3 m per 45-degree elbow when checking long runs against the sizing table.

A wet vent may serve only fixtures on the same storey and must be sized as a combination drain and vent; it cannot serve a water closet unless the code explicitly permits it.

Water hammer arrestors are required at quick-closing valves such as solenoid and flush valve installations; size the arrestor to the fixture unit load of the branch.

Thermal expansion: a 100 m length of copper pipe heated 50 degrees Celsius expands about 84 mm; install expansion loops or offsets where the calculated movement exceeds the allowance.

Hot water delivery temperature at the outlet should not exceed 50 degrees Celsius at the fixture for sanitary use; tempering valves are required at the outlet of storage water heaters set above 60 degrees Celsius.

Storm drainage sizing uses the rainfall intensity for the site, the roof catchment area, and the code's table for leader and gutter capacity; the design storm is usually a 1-in-100 year event for the local jurisdiction.

Cross-connection control: every connection to a potable system must be protected by an air gap or a testable backflow assembly, and the assembly must be tested at commissioning and at the interval set by the authority.

Gas appliance input ratings are given in MJ/h at the rated manifold pressure; a typical domestic cooktop is about 20 to 30 MJ/h total, a storage water heater 150 to 200 MJ/h, and a ducted space heater 100 to 150 MJ/h.

Pipe capacity tables are based on the allowable pressure drop, the specific gravity of the gas, and the pipe material; copper, steel, and polyethylene have different roughness and therefore different capacities for the same diameter.

A gas regulator reduces supply pressure to the appliance manifold pressure, typically 1.0 kPa for natural gas appliances and 2.75 kPa for propane; a regulator must be vented to a safe location outdoors or to a ventilated space.

Appliance clearances: a gas appliance must be installed to the manufacturer's clearances from combustible surfaces, and the flue must maintain the code clearance from combustible construction.

Isolation valves must be installed on the supply to each appliance and be accessible; a union or flanged connection is required downstream of the valve for service.

Gas piping must be supported at intervals set by the code, typically every 1.8 m for horizontal runs and at each change of direction, and must not be concealed in a way that prevents inspection.

A gas appliance in a bedroom or bathroom must be of the room-sealed or balanced-flue type; open-flue appliances are not permitted in those spaces because of the combustion products risk.

Purging and commissioning: after testing, purge the line with gas to a safe point, check the operating pressure at the appliance, and verify the flame and combustion readings before handover.

Pipe sizing for water supply uses the equivalent length method: convert fittings to equivalent pipe length, add to the actual run, then use the pressure drop per metre and the available pressure to select the diameter.

A drainage stack must be vented at the top and must extend at least 150 mm above the roof or to the code's required height; the vent terminal must be clear of windows and air intakes.

Grease traps are required for commercial kitchen fixtures and must be sized by the fixture unit load and the retention time; the trap must be accessible for cleaning and inspection.

Sanitary drainage must not connect to storm drainage; separate systems are required, and any combined system must be approved by the authority having jurisdiction.

A cleanout is required at the base of each stack, at each change of direction greater than 45 degrees, and at intervals not exceeding 15 m on horizontal runs.

Water meters and backflow assemblies must be protected from freezing and from vehicle impact; install a strainer upstream of the meter and a bypass where service continuity is required.

Testing of the drainage system may use water, air, or smoke; the air test is typically 35 to 50 kPa and the water test is a 3 m head, held for the period set by the code.

Fixture traps must be self-cleaning and must not be double-trapped or double-vented; a single trap may serve a set of fixtures only where the code allows a common trap.

Water supply pipe material selection depends on the water chemistry: copper is affected by low pH and high chloride, while PEX is affected by chlorine and UV exposure; check the water analysis before choosing.

Gas load calculation: sum the input ratings of all appliances, then apply the diversity factor permitted by the code; the meter and service must be sized for the diversified load, not the connected load.

The gas meter must be located outdoors or in a ventilated space and must be accessible; the meter outlet must be fitted with a regulator and a shut-off valve before the piping enters the building.

A gas line must not pass through a duct, a chimney, or a lift shaft; where it passes through a wall or floor, it must be protected by a sleeve and the annular space sealed.

Flame failure devices are required on all gas appliances except those with a permanent pilot and a proven safety record; a thermocouple or flame rectification sensor shuts off the gas if the flame is lost.

Carbon monoxide is produced by incomplete combustion; appliances must be adjusted to the manufacturer's CO2 and CO readings, and a CO alarm is required in the room containing the appliance in many jurisdictions.

Gas piping in a trench or underground must be protected against corrosion and must be bedded and backfilled to the code's requirements; a tracer wire or marker tape is required for polyethylene pipe.

The gas installation must be bonded to the electrical earth; a bonding conductor sized per the electrical code is connected to the gas piping at the point of entry.

A gas appliance must not be installed in a room without adequate ventilation; the room must have permanent openings sized for the combustion air and dilution air requirements of the appliance.

The fixture unit method is only valid within the range of the table; for large systems above the table limit, use the peak demand method based on fixture counts and probability.

A vent stack and a stack vent are different: the stack vent is the extension of the soil stack above the highest fixture, while a vent stack is a separate vertical vent serving a group of fixtures.

The developed length of a trap arm from the fixture outlet to the vent connection must not exceed the code limit, typically 1.5 m for a 40 mm trap and 1.8 m for a 50 mm trap.

A building drain must be laid at a uniform slope and must not change direction by more than 45 degrees without a cleanout; a 90-degree change requires a wye and a 45-degree bend, not a tee.

Water pressure at the fixture must be within the manufacturer's range; where the supply pressure exceeds 500 kPa, a pressure-reducing valve is required on the supply.

A water heater must be fitted with a temperature and pressure relief valve, a relief drain piped to a safe discharge point, and an expansion control valve where the supply is closed.

Rainwater harvesting and greywater systems must be fully separated from potable water, with distinct pipe colouring and signage, and must be protected by an air gap at the storage tank inlet.

A plumbing installation must be inspected at the rough-in stage before concealment; the inspector checks the pipe sizes, slopes, venting, and the pressure test record.

Gas pipe sizing must account for the pressure at the meter: low-pressure systems are sized at the meter outlet pressure, while medium-pressure systems are sized at the regulator outlet and require a regulator at each appliance.

The gas pipe must be installed with a fall to a dirt pocket or drip leg at the appliance connection; the drip leg collects condensate and debris and must be accessible for cleaning.

A gas appliance connector must be of the approved type, must not pass through a wall, floor, or ceiling, and must not be concealed; the connector length is limited by the code.

Gas piping must be tested before the meter is connected and again after the appliances are connected; the test pressure and duration are set by the code and recorded on a test certificate.

A gas leak is detected by smell, by a bubble test on joints, or by an electronic detector; a leak must be isolated, repaired, and retested before the gas is restored.

The gas installation must be commissioned by a licensed person who checks the operating pressure, the gas rate, the combustion readings, and the safety devices, and who provides a compliance certificate.

Gas appliances must be installed to the manufacturer's instructions, which take precedence over the code where they are more stringent; keep the instructions on site for the inspector.

A gas appliance in a commercial kitchen must have a grease filter, a fire suppression system, and an interlock that shuts off the gas on activation of the suppression system.

The minimum size of a building sewer is 100 mm; the minimum size of a building drain is 100 mm, and the minimum size of a soil stack is 75 mm unless the code permits smaller for a single fixture.

A vent must terminate at least 150 mm above the roof and at least 3 m from an air intake or window, or to the distance set by the code, whichever is greater.

A backwater valve is required on the building drain where the fixture level is below the level of the street sewer; the valve must be accessible for maintenance.

A sump pump must discharge to a safe point outside the building and must not connect to the sanitary sewer unless the code permits it; the discharge must not create a nuisance or erosion.

A water supply system must be flushed and disinfected after installation; the disinfectant is typically a chlorine solution at 50 mg/L for 24 hours, followed by a flush to clear residual.

A plumbing fixture must be installed level and secure, with the trap accessible, and must be sealed to the wall or floor with a waterproof joint where required.

A grease interceptor must be sized by the fixture unit load and the retention time, and must be pumped out at the interval set by the authority; records of pump-out must be kept.

A plumbing system must be designed so that it can be drained down; provide drain valves at low points and slope the pipe to the drain point.

The gas meter and regulator must be sized for the diversified load and the pressure drop; the regulator must be vented to a safe location and must not be installed in a pit or a confined space.

A gas appliance must be connected to a flue that is sized for the appliance input and the flue height; an undersized flue causes spillage of combustion products into the room.

A gas appliance must have a clearance from a combustible surface that meets the manufacturer's instructions and the code; a clearance plate or a ventilated air space may be required.

A gas pipe must be protected against mechanical damage where it is exposed, and must not be used as an earthing electrode or as a support for other services.

A gas installation must be provided with a shut-off valve at the meter and at each appliance; the valve must be accessible and must be labelled.

A gas appliance must be tested for spillage at the flue after installation; a smoke test or a mirror test confirms that the combustion products are being carried away.

A gas appliance in a residential garage must be installed so that the ignition source is at least 450 mm above the floor, because petrol vapour is heavier than air.

A gas installation must be maintained and inspected at the interval set by the authority; the inspection covers the pipework, the appliance, the flue, and the safety devices.