Building Services (Mechanical, Electrical, Plumbing)
Water, drainage and electricity
Services questions test sizing and the principles that keep a building safe and habitable. Water: estimate demand from occupancy (typically 150-200 litres per person per day for domestic use), size storage for at least a day plus any fire reserve, and provide a cold-water downfeed with a vented tank, gate valves and a washout. Drainage: separate soil and waste, ventilate the stack, lay drains at self-cleansing gradients of about 1:60 to 1:110, and pass them through inspection chambers to a septic tank, soakaway or public sewer. Electrical: build a load schedule, apply diversity, and provide earthing, RCD protection, surge protection and a changeover for generator or inverter supply.
Comfort and fire
Ventilation: 6-12 air changes per hour for kitchens and bathrooms, cross-ventilation for habitable rooms. Lighting: design to maintained illuminance, about 300 lux for offices and 100-150 lux for circulation. Fire: escape route widths and travel distances, detection, extinguishers, and hydrant or hose reel provision for larger buildings.
Worked example
A 6 m x 8 m office, 48 m², needs 300 lux. Each luminaire gives 4,000 lumens; utilisation factor 0.6, maintenance factor 0.8. N = (E x A) / (UF x MF x lumens) = (300 x 48) / (0.6 x 0.8 x 4,000) = 14,400 / 1,920 = 7.5, so install 8 luminaires in a layout that follows the workstations.
Traps
Sizing a tank from bedroom count rather than occupancy and demand; omitting the vent pipe or trap; comparing watts instead of lux; ignoring diversity in the load schedule.