Building Services (Mechanical and Electrical)
Services questions span Mabhas 13 (mechanical installations), the electrical chapter, lifts and escalators, energy conservation (Mabhas 19) and fire systems under Mabhas 3. The exam tests whether you can size, coordinate and inspect systems, not merely name them.
Core rules
- Water and drainage: storage is sized from occupancy and daily demand plus fire reserve; soil and waste stacks need correct slopes, venting and cleanouts; pipework is pressure-tested before concealment.
- HVAC: ventilation rates follow occupancy; ducts and shafts must be coordinated with structure and fire compartmentation; flues and chimneys need correct height and termination.
- Electrical: earthing, protective bonding, panel accessibility, separation of risers, and protection of wet-area circuits.
- Lifts: car and door dimensions, machine-room or machine-room-less requirements, pit depth and headroom are design inputs that must exist before the shaft is poured.
- Energy: envelope insulation, glazing performance and equipment efficiency are compliance items under Mabhas 19.
Worked example
A residential block houses 40 people; design demand is taken as 150 litres per person per day → 6000 litres daily. With one day's storage plus a fire reserve of, say, 5000 litres, the tank volume is 6000 + 5000 = 11,000 litres. Useful volume is less than nominal, so specify the tank from its effective capacity and place the float valve and overflow so the fire reserve is not drawn off by domestic use - a classic coordination error.
Traps
Sizing storage from nominal rather than effective tank volume. Concealing pipework before pressure testing. Forgetting that shafts and ducts penetrate fire compartments and need sealing. Discovering lift pit and headroom requirements after the shaft is built.