What is services planning?
A building service is a system that makes a building work: water, drainage, air, power, fire safety and lifts. Services planning means deciding early which systems the building needs, how big they are and where they will run.
Planners follow three questions: What does the building need (people, use, climate)? Where will each system run? How much space does it take?
The plan is made together with the architect and the structure designer. Late plans cause cutting of walls and beams, extra cost and delays.
Planning the various services
- Water supply: a tank on the roof or a pump pushes water to taps. Pressure is p = ρgh, about 1 bar for every 10 m of height.
- Drainage: waste water flows by gravity, so pipes must slope downwards. A vent pipe lets air in so that water flows smoothly.
- Air conditioning and ventilation: ducts carry cool and fresh air. They are large, so they are planned first.
- Electrical: cables run in trays and conduits; panels need safe, dry rooms.
- Fire safety and lifts: sprinklers, alarms, fire pipes and lift shafts need fixed positions.
A good order is: biggest and least flexible first (ducts, drains), then pipes, then cables.
Space for equipment and piping
Services need three kinds of space:
- Vertical shafts for risers that go through all floors.
- Ceiling void (gap above the false ceiling) for horizontal ducts, pipes and trays.
- Machine rooms for pumps, chillers, fans and electrical panels, with room around them for repair.
Headroom check: headroom = floor to floor height - slab or beam depth - duct depth - ceiling gap. A normal room should have about 2.4 m headroom. If it is less, make the ducts shallower and wider, or raise the floor height.
Slope check: a drain slope of 1 in 100 drops 1 cm for every metre of pipe length.
Planning with the structure and the climate
Climate and building shape decide the size of the services: a hot, sunny building needs bigger cooling ducts; a tall building needs pumps to lift water. Beams and columns carry the load, so openings through them must be planned with the structure designer and never cut on site. A shaft that is too small can not be fixed later, so leave some extra room for future pipes.
Key formulas and definitions
- Headroom = floor to floor - beam - duct - gap
- Drain drop = pipe length x slope (1 in 100 means 0.01)
- Water pressure p = rho x g x h (rho = 1000 kg/m3, g = 9.8 m/s2)
- Flow Q = A x v (area x speed)
Worked examples
1. Floor to floor is 3.2 m. Beam 0.5 m, duct 0.4 m, gap 0.1 m. Find the headroom.
Headroom = 3.2 - 0.5 - 0.4 - 0.1 = 2.2 m. This is below 2.4 m, so use a shallower duct or a taller floor.
2. A drain 12 m long has a slope of 1 in 50. How much does it drop?
Drop = 12 x 1/50 = 0.24 m = 24 cm.
3. A tank is 20 m above a tap. Find the pressure at the tap.
p = 1000 x 9.8 x 20 = 196,000 Pa = 196 kPa, about 2 bar.
4. A pipe of inside diameter 50 mm carries water at 1.5 m/s. Find the flow in L/s.
A = 3.14 x 0.025^2 = 0.001963 m2. Q = 0.001963 x 1.5 = 0.00294 m3/s = 2.94 L/s.
Common mistakes
- Planning services after the building design is fixed.
- Forgetting the beam depth when counting headroom.
- Giving a drain pipe no slope, so water stands in it.
- Putting machines in a room with no space to repair them.