Building Services (Plumbing, Electrical, Drainage)
What the domain tests
Building Services tests water supply, sanitary fittings, traps, drainage gradients, inspection chambers, electrical circuits, earthing and safety.
Core rules
- Water supply includes a stop valve, meter where fitted, storage and distribution pipework. Protect pipes from damage and lag where needed.
- Traps hold a water seal to stop sewer gas entering the building. P-traps and S-traps must be ventilated to prevent siphonage.
- Soil and waste drainage should be separate where required. Use the specified gradient, commonly around 1:60 for a 100 mm drain.
- Provide inspection chambers at changes of direction, junctions and long runs; include rodding eyes.
- Electrical circuits use live, neutral and earth conductors with correct colour identification. RCDs and earthing are essential safety measures.
- Co-ordinate service openings and sleeves before concrete is placed.
Worked example
A drain runs 12 m at a gradient of 1:60. Fall = 12/60 = 0.2 m = 200 mm. If the upstream invert is 100.00 m, the downstream invert is 99.80 m. Reasoning: gradient is a ratio of fall to length; subtract the fall in the direction of flow.
Traps
- Connecting a soil appliance without a trap.
- Laying drains too flat or with a backfall.
- Using the earth conductor as a neutral.
- Omitting an inspection chamber at a bend.
- Forgetting to cap or sleeve services through walls.