I85PREP
⌘ K
OBC Building Services study materials
OBC Building Services study resources

OBC Building Services practice questions

One question at a time. Build your OBC Building Services understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Building Services

In a domestic cold-water supply system, what is the main purpose of a float-operated valve in a cold-water storage cistern?

  1. To boost the incoming mains pressure to the upper floors
  2. To maintain the stored water level by closing the inlet when the cistern is full Correct answer.
  3. To filter sediment from the incoming supply
  4. To prevent warm water from back-siphoning into the cold feed

Explanation

A float-operated valve senses the water level through a floating arm and shuts off the incoming supply once the set level is reached, then reopens as water is drawn off. This keeps a usable reserve while preventing overflow. It does not control pressure, temperature or filtration.

Question 2Building Services

Which type of valve is best suited to isolating a section of pipework quickly while giving a clear visual indication of whether it is open or shut?

  1. A pressure-reducing valve
  2. A gate valve
  3. A float-operated valve
  4. A lever-operated butterfly valve Correct answer.

Explanation

A quarter-turn lever handle on a butterfly valve shows at a glance whether the disc is open or closed and allows rapid isolation. Gate valves need many turns and give no immediate visual position. Pressure-reducing and float valves serve other functions entirely.

Question 3Building Services

In a vented (open) central heating system, what is the function of the feed-and-expansion cistern?

  1. To store hot water for domestic use
  2. To increase the circulation pressure around the radiators
  3. To absorb the expansion of heated water and keep the system full Correct answer.
  4. To separate air from the boiler flue gases

Explanation

When water is heated it expands, and in an open system the surplus volume rises into the feed-and-expansion cistern. As the system cools, water returns to keep the pipework full. The cistern is not a domestic hot-water store and does not drive circulation.

Question 4Building Services

What is the primary reason for installing a trap beneath a sanitary appliance?

  1. To reduce the noise of discharging water
  2. To store water for flushing the appliance
  3. To retain a water seal that prevents sewer gases entering the building Correct answer.
  4. To increase the flow rate of waste water

Explanation

A trap holds a small body of water in its dip, and this seal blocks the passage of foul air and gases from the drainage system back into the room. The depth of seal is the critical feature. Traps do not store flush water or appreciably boost flow.

Question 5Building Services

Which document type is used to record that a newly installed electrical circuit has been tested and is safe to energise?

  1. A minor works certificate
  2. An electrical installation certificate Correct answer.
  3. A building log book
  4. A method statement

Explanation

An electrical installation certificate is issued for new circuits and records the design, construction and test results confirming safety. A minor works certificate covers small alterations to existing circuits. A log book and a method statement serve different purposes.

Question 6Building Services

What does the term 'dead leg' describe in a domestic water system?

  1. A pipe run that supplies only cold water
  2. An insulated section of the hot-water circuit
  3. A section of pipe buried below ground level
  4. A pipe branch that carries no flow and allows water to stagnate Correct answer.

Explanation

A dead leg is a length of pipe connected to the supply but not drawn through in normal use, so water sits in it and can stagnate. Stagnation raises the risk of bacterial growth such as legionella. The term refers to flow, not burial depth or temperature.

Question 7Building Services

Which fire-protection measure is classed as 'active' rather than 'passive'?

  1. An automatic sprinkler system Correct answer.
  2. Intumescent seals around a fire door
  3. A fire-resisting compartment wall
  4. A protected escape stair

Explanation

Active measures require a detection or activation step to operate, and a sprinkler system releases water only when a head fuses. Passive measures such as compartment walls, protected stairs and intumescent seals work by their built-in resistance without needing activation.

Question 8Building Services

In a pumped heating circuit, what is the role of a bypass (automatic bypass valve) around the boiler?

  1. To vent air from the highest point
  2. To drain the system for maintenance
  3. To mix cold water into the hot supply
  4. To allow water to circulate when terminal valves close, protecting the boiler from low flow Correct answer.

Explanation

When thermostatic valves shut down most of the load, flow through the boiler can fall below its minimum, causing overheating or noisy operation. A bypass valve opens to maintain flow. It does not drain the system or blend domestic water.

Question 9Building Services

A cold-water storage cistern is located in a roof space. Which arrangement correctly protects the potable supply from contamination?

  1. The inlet discharges below the water line with no gap
  2. The warning pipe is connected to the drain
  3. The inlet discharges above the overflow level with a visible air gap Correct answer.
  4. The overflow discharges into a soil pipe

Explanation

Discharging the inlet above the highest possible water level, with a physical air gap, prevents back-siphonage of cistern water into the mains. This is the standard backflow protection for a storage cistern. Discharging below the waterline or connecting the overflow to a soil pipe creates contamination paths.

Question 10Building Services

A hot-water cylinder is fed from a cold-water cistern whose water level is 3 m above the cylinder. What is the approximate static pressure at the base of the cylinder, ignoring losses?

  1. About 3 kPa
  2. About 30 kPa Correct answer.
  3. About 0.3 kPa
  4. About 300 kPa

Explanation

Static pressure equals the water column height multiplied by density and gravity: 3 m x 1000 kg/m3 x 9.81 m/s2 is about 29.4 kPa, roughly 30 kPa. Each metre of water head gives close to 10 kPa. The other values are out by factors of ten.

Question 11Building Services

Why must the water seal of a trap be protected against self-siphonage where a long unvented branch connects to a stack?

  1. Because the water will become too hot in the branch
  2. Because the discharge can create a pressure drop that pulls the seal out Correct answer.
  3. Because the seal will evaporate faster in long pipes
  4. Because the trap will become blocked with debris

Explanation

When a slug of water falls down a branch and stack, it can generate a partial vacuum behind it that draws the trap seal away, breaking the barrier. Venting the branch equalises pressure and preserves the seal. Evaporation, blockage and temperature are separate concerns.

Question 12Building Services

A room contains a gas-fired boiler in a compartment with a high-level and a low-level ventilation opening. Why are two openings at different levels normally required?

  1. To give access for servicing the boiler
  2. To balance the pressure in the domestic water system
  3. To provide a route for the flue to pass through the wall
  4. To allow both combustion air in and heat to escape by convection Correct answer.

Explanation

A low-level opening supplies cool combustion air, while a high-level opening lets warmed air and any leakage escape, driving a convective flow through the compartment. This keeps the appliance supplied and prevents overheating. Neither opening is a flue route or a servicing access.

Question 13Building Services

Which condition most strongly increases the risk of legionella growth in a domestic hot-water system?

  1. Storing water at 60 degrees Celsius in the cylinder
  2. Regularly drawing water from all outlets
  3. Fitting thermostatic mixing valves at outlets
  4. Water temperatures between about 20 and 45 degrees Celsius with stagnation Correct answer.

Explanation

Legionella bacteria multiply most readily in warm water within roughly 20 to 45 degrees Celsius, especially where water sits still. Storing hot water at 60 degrees Celsius and drawing all outlets regularly both reduce the risk. Outlet blending valves limit delivery temperature but do not by themselves create the growth conditions.

Question 14Building Services

A small commercial kitchen requires an extract system for cooking fumes. Which combination best describes a suitable arrangement?

  1. A supply-only ventilation system
  2. An openable window only
  3. An extract hood ducted to outside with a grease filter and a fan sized for the hood Correct answer.
  4. A recirculating filter hood with no external discharge

Explanation

Cooking fumes, grease and moisture should be captured at the hood and ducted to outside, with grease filtration protecting the duct and a fan matched to the hood's required extract rate. Recirculation cannot remove moisture and heat effectively, and supply-only ventilation will not capture fumes at source.

Question 15Building Services

In a drainage system, what is the purpose of a rodding eye?

  1. To prevent roots entering the pipe
  2. To allow air into the system during discharge
  3. To provide access for clearing a blockage in the drain run Correct answer.
  4. To measure the flow rate in the drain

Explanation

A rodding eye is an access point, usually at the end of a run or at a junction, through which rods can be inserted to clear obstructions. It is not an air admittance device and does not measure flow. Root protection is a separate concern.

Question 16Building Services

A ring final circuit in a dwelling is protected by a 32 A device. Why is this arrangement acceptable despite the cable rating being lower than 32 A?

  1. Because the protective device never operates
  2. Because the load is shared along two paths to each socket, so no single cable section carries the full current Correct answer.
  3. Because the sockets are rated at 32 A each
  4. Because the cable is always installed in free air

Explanation

In a ring final circuit each socket is fed by two legs, so current divides between them and no cable section normally carries the full circuit current. This is why a 32 A device can protect smaller conductors in this specific topology. The device does operate on fault, and installation method or socket rating do not explain the arrangement.

Question 17Building Services

What is the main purpose of a residual current device (RCD) in a domestic installation?

  1. To correct the power factor of inductive loads
  2. To disconnect the supply when earth-leakage current exceeds a set value Correct answer.
  3. To step down the mains voltage for lighting
  4. To limit the total current drawn by the installation

Explanation

An RCD compares current in the live and neutral conductors and trips when an imbalance, indicating leakage to earth, exceeds its rated sensitivity. This provides additional protection against electric shock and fire. It does not limit normal load current or change voltage.

Question 18Building Services

In a sealed (unvented) heating system, what is the function of the expansion vessel?

  1. To accommodate the increased volume of water as it heats, limiting pressure rise Correct answer.
  2. To store domestic hot water under pressure
  3. To remove air from the radiators automatically
  4. To act as a second feed cistern

Explanation

A sealed system has no open cistern, so the expansion vessel contains a gas charge separated by a diaphragm that compresses as water expands. This absorbs the extra volume and keeps system pressure within safe limits. It does not store domestic water or replace a feed cistern.

Question 19Building Services

A fire door is fitted with a self-closing device and intumescent strips. Why must the door not be wedged open during normal use?

  1. Because the self-closer will overheat
  2. Because wedging increases wear on the hinges
  3. Because the intumescent strips will activate prematurely
  4. Because an open door allows fire and smoke to spread through the compartment line Correct answer.

Explanation

A fire door protects a compartment or escape route only when closed, so holding it open defeats its purpose and allows smoke and fire to pass. Intumescent strips expand only when heated, and hinge wear is not the safety issue. Approved hold-open devices release on alarm.

Question 20Building Services

Which factor most affects the required size of a cold-water storage cistern in a dwelling?

  1. The colour of the cistern body
  2. The height of the cistern above the taps
  3. The number of occupants and the daily water demand to be stored Correct answer.
  4. The length of the overflow pipe

Explanation

Cistern capacity is set by the volume of water that must be held to cover demand between refills, which depends on occupancy and usage. Colour, overflow length and mounting height do not determine stored volume, although height affects pressure at outlets.

Question 21Building Services

A discharge pipe from a temperature relief valve on an unvented cylinder must be routed to a safe place of discharge. Which requirement applies?

  1. It must rise continuously to a high-level outlet
  2. It may terminate inside the cylinder cupboard
  3. It may be connected directly to a soil stack
  4. It must fall continuously to a safe, visible point outside the building Correct answer.

Explanation

The relief discharge must be able to flow away by gravity without trapping water, so it falls continuously to a safe and visible termination outside, typically above a gully. Connecting to a soil stack risks contamination, and terminating indoors would release hot water and steam into the building.

Question 22Building Services

A heating system shows a pressure gauge reading that rises significantly only when the boiler is running and returns when it cools. Which explanation is most consistent with this behaviour?

  1. The room thermostat is faulty
  2. The pump is set to too low a speed
  3. The radiator valves are all fully open
  4. The expansion vessel has lost its gas charge or is undersized Correct answer.

Explanation

Pressure that climbs with temperature and falls on cooling points to inadequate expansion accommodation, commonly a lost gas charge or an undersized vessel. The water has nowhere to expand into, so pressure spikes when hot. Pump speed, thermostat faults and valve position would not produce this pattern.

Question 23Building Services

Two identical rooms are ventilated, one by natural ventilation and one by mechanical extract. Which statement best explains why the mechanical system gives more predictable air-change rates?

  1. Mechanical systems remove less air per hour
  2. Mechanical systems always use larger openings
  3. Mechanical systems do not depend on wind and temperature differences to drive airflow Correct answer.
  4. Mechanical systems only operate when windows are open

Explanation

Natural ventilation relies on wind pressure and stack effect, both of which vary with weather, so achieved airflow fluctuates. A fan delivers a defined volume flow largely independent of those driving forces, making the air-change rate more predictable. Opening size and window position do not explain the difference.

Question 24Building Services

A drainage stack serving several floors is fitted with an air admittance valve at the top rather than an open vent. What is the effect on the system?

  1. It allows air in to relieve negative pressure but prevents foul air escaping Correct answer.
  2. It replaces the need for any trap seals
  3. It increases the discharge velocity in the stack
  4. It allows foul air to escape freely to atmosphere

Explanation

An air admittance valve opens under negative pressure to admit air and protect trap seals, then closes to stop foul air escaping into the building. It does not provide an open path to atmosphere and cannot substitute for trap seals. It does not change discharge velocity.

Question 25Building Services

A large open-plan office has high internal gains and a glazed facade. Which control strategy best balances energy use with occupant comfort in summer?

  1. Keeping all windows closed and relying on internal air movement only
  2. Running the heating and cooling simultaneously at fixed setpoints
  3. Operating the ventilation at constant maximum rate regardless of occupancy
  4. Using temperature and CO2 sensors to modulate mechanical cooling and ventilation Correct answer.

Explanation

Demand-based control using temperature and CO2 feedback adjusts cooling and fresh-air supply to actual conditions, saving energy when loads are low while maintaining comfort. Simultaneous heating and cooling wastes energy, and constant maximum ventilation ignores occupancy. Sealed windows with no air movement would allow overheating.

Question 26Building Services

Which document is the primary source of technical guidance for complying with the Building Regulations in England when designing building services?

  1. Manufacturer installation manuals
  2. British Standards catalogue
  3. Approved Documents Correct answer.
  4. The Building Safety Act

Explanation

Approved Documents are issued by government to give practical guidance on how the functional requirements of the Building Regulations can be met. They are not themselves law, but following them is normally accepted as evidence of compliance.

Question 27Building Services

In a domestic hot-water system, what does the term 'primary circuit' refer to?

  1. The pipework carrying water from the heat source to the cylinder coil Correct answer.
  2. The pipework delivering hot water to the taps
  3. The overflow pipe from the feed-and-expansion tank
  4. The cold feed to the storage cistern

Explanation

The primary circuit transfers heat from the boiler or other heat source to the stored water, usually through a cylinder coil or heat exchanger. The secondary circuit is the water drawn to the outlets.

Question 28Building Services

Which material is typically used for underground drainage pipes because it resists corrosion in soil?

  1. Copper
  2. Galvanised steel
  3. Cast iron
  4. uPVC Correct answer.

Explanation

Unplasticised polyvinyl chloride is widely used for below-ground drainage because it is light, smooth-bored and resistant to chemical attack in soil. It also keeps friction losses low for gravity flow.

Question 29Building Services

Why is a trap fitted to a sanitary appliance connected to a drainage system?

  1. To filter solid matter before it enters the stack
  2. To provide a rodding access point for blockages
  3. To retain a water seal that blocks foul air from the drain Correct answer.
  4. To regulate the flow rate into the branch pipe

Explanation

A trap holds a measured depth of water that prevents sewer gases and odours from travelling back into the room. The seal must be deep enough to resist pressure fluctuations in the drainage system.

Question 30Building Services

What is the primary function of a room thermostat in a domestic heating system?

  1. To limit the temperature of water leaving the boiler
  2. To balance the flow rate through each radiator
  3. To switch the heating on and off according to the room air temperature Correct answer.
  4. To measure outside air temperature and adjust the boiler output

Explanation

A room thermostat senses the air temperature in its location and makes or breaks the call for heat to keep the room near the set point. This prevents the boiler running continuously once the space is warm.

Question 31Building Services

Which unit is used to express the sound pressure level produced by a building service such as a fan?

  1. Pascal second (Pa·s)
  2. Decibel (dB) Correct answer.
  3. Lux (lx)
  4. Kilowatt-hour (kWh)

Explanation

Sound pressure level is expressed in decibels, a logarithmic ratio relative to a reference pressure. Noise from plant is commonly assessed in dB(A) to reflect the sensitivity of the human ear.

Question 32Building Services

What is the main purpose of a fire-resisting compartment wall in a building?

  1. To support the weight of roof-mounted plant
  2. To reduce heat loss from the building fabric
  3. To provide a route for service pipes between floors
  4. To contain fire and smoke within a defined area for a stated period Correct answer.

Explanation

Compartmentation divides a building into fire-resisting zones so that fire and smoke are held back, protecting escape routes and limiting spread. The wall must achieve a stated fire resistance period, typically in minutes.

Question 33Building Services

Which type of cable is normally required for a circuit supplying a fixed electric shower in a domestic bathroom?

  1. Bell wire protected by a 6 A MCB
  2. Flexible cord with a 3 A fuse
  3. Twin and earth cable sized for the load, with local isolation Correct answer.
  4. Coaxial cable with an earth screen

Explanation

A fixed shower needs a dedicated circuit with cable sized for its current demand and a means of local isolation for maintenance. Protection and supplementary bonding must also suit the location.

Question 34Building Services

A dwelling has a cold-water cistern feeding a vented hot-water cylinder. If the cistern water level is 5 m above the cylinder, what static pressure does the cylinder base experience?

  1. About 50 kPa
  2. About 0.05 bar
  3. About 5 bar
  4. About 0.5 bar Correct answer.

Explanation

Static pressure from a head of water is approximately 0.1 bar per metre of height. A 5 m head therefore gives roughly 0.5 bar at the base of the cylinder.

Question 35Building Services

A condensing boiler is to be installed with a horizontal flue. Which arrangement best supports efficient condensing operation?

  1. A flue with the terminal fitted below the air intake
  2. A flue terminating inside a covered carport
  3. A long flue falling back toward the boiler with a drain connection Correct answer.
  4. A short flue with a steep upward slope away from the boiler

Explanation

Condensing boilers recover latent heat when the flue gases cool and the resulting condensate must be drained away. A flue falling back to the boiler with a suitable condensate trap and drain allows this to happen safely.

Question 36Building Services

A soil and vent stack serves a block of flats. Which measure best prevents induced siphonage of traps on lower floors?

  1. Reducing the number of appliances on each branch
  2. Providing a ventilated stack with a connection to outside air at the top Correct answer.
  3. Fitting shallow traps with a 25 mm seal
  4. Increasing the diameter of each branch waste pipe

Explanation

Pressure fluctuations in a discharge stack can pull the water seal from traps. Venting the stack to outside air equalises pressure and protects the seals on all connected branches.

Question 37Building Services

A small office has a floor area of 60 m² and a ceiling height of 2.7 m. Using a ventilation rate of 10 litres per second per person with a design occupancy of 8 people, what is the required outdoor air supply?

  1. 48 L/s
  2. 800 L/s
  3. 80 L/s Correct answer.
  4. 18 L/s

Explanation

The requirement is calculated by multiplying the per-person rate by the number of occupants. Eight people at 10 L/s each gives 80 L/s of outdoor air.

Question 38Building Services

In a domestic electrical installation, what is the purpose of main protective bonding of incoming metal services?

  1. To replace the need for circuit protective conductors
  2. To ensure metal pipes and cables are at the same potential, limiting touch voltage Correct answer.
  3. To reduce electricity bills by improving earthing efficiency
  4. To provide a return path for fault current through the water pipe

Explanation

Main protective bonding connects incoming metallic services to the main earthing terminal so that they sit at substantially the same potential. This limits the voltage that can appear between simultaneously accessible metal parts during a fault.

Question 39Building Services

A luminaire is described as having a utilisation factor of 0.5 in a room. What does this indicate?

  1. Half the lamps in the fitting will operate at any one time
  2. Half the lamp lumens reach the working plane from the luminaire and room surfaces Correct answer.
  3. The fitting consumes half its rated power in standby
  4. The lamp has a colour rendering index of 50

Explanation

The utilisation factor expresses the proportion of lamp output that reaches the working plane, allowing for luminaire efficiency and room surface reflectance. It is used with the lumen method to size lighting installations.

Question 40Building Services

A fire alarm system in a large hotel uses detectors in bedrooms and call points at exits. Which feature is essential so occupants are warned before conditions become untenable?

  1. Detectors installed only in corridors
  2. Audible and visual alarms throughout, with staged evacuation as designed Correct answer.
  3. A delay of at least 10 minutes before sounders operate
  4. Sounders located only at the main reception

Explanation

An alarm must give warning throughout the protected area so people can begin escape before smoke or heat becomes dangerous. In complex buildings, a staged or phased evacuation may be designed to suit the occupancy.

Question 41Building Services

A pump serving a heating circuit is noisy and the differential pressure across it is higher than design. Which adjustment is most appropriate?

  1. Close the system fill valve permanently
  2. Remove the automatic air vent from the circuit
  3. Reduce the pump speed to match the design duty Correct answer.
  4. Increase the pump speed to overcome the noise

Explanation

Excessive pump head usually means the pump is oversized for the circuit, causing high water velocity and noise. Reducing the speed, where the pump allows it, brings the duty closer to design and lowers noise.

Question 42Building Services

Which arrangement best protects a cold-water storage cistern from contamination by backflow?

  1. A submerged inlet pipe below the water line
  2. A sealed lid with the overflow connected to the drain
  3. A cistern located below the level of the appliances it serves
  4. An inlet with an air gap above the highest water level Correct answer.

Explanation

An air gap between the inlet and the maximum water level prevents any backflow from the cistern into the supply. This is a robust, non-mechanical form of backflow protection.

Question 43Building Services

A sealed heating system with a 12 m static head is being filled. The expansion vessel pre-charge should be set to approximately what value?

  1. 1.2 bar Correct answer.
  2. 6.0 bar
  3. 3.0 bar
  4. 0.5 bar

Explanation

The pre-charge is normally set close to the static pressure at the vessel plus a small margin. A 12 m head is about 1.2 bar, so setting the pre-charge near this value allows the vessel to absorb expansion correctly.

Question 44Building Services

In a commercial kitchen, why is a grease filter fitted at the canopy of an extract system?

  1. To cool the extracted air before discharge
  2. To provide fresh air into the kitchen
  3. To increase the extract fan speed
  4. To reduce the fire risk by capturing grease before it enters the duct Correct answer.

Explanation

Grease carried into ductwork can accumulate and ignite, so filters at the canopy remove much of it close to the source. Ductwork must also be accessible for cleaning to control the remaining fire risk.

Question 45Building Services

A room has a high sensible heat gain and a low latent gain. Which terminal unit is best suited to maintain comfort without excessive dehumidification?

  1. A chilled water fan coil unit with a dry cooling coil Correct answer.
  2. A radiant panel with no cooling capacity
  3. A natural-draught ventilator
  4. A direct-expansion unit sized only for latent load

Explanation

A sensible-dominated load is best met by cooling the air without taking it below its dew point, so a dry fan coil avoids unnecessary dehumidification. This maintains comfort while controlling energy use.

Question 46Building Services

A building's drainage system includes a pumped sump for a basement toilet. Which safeguard is essential to prevent sewage flooding the basement if the pump fails?

  1. A larger diameter discharge pipe
  2. A non-return valve and an alarm with a high-level cut-out Correct answer.
  3. A vent pipe terminating inside the plant room
  4. A shallow trap on the sump inlet

Explanation

Where drainage relies on pumping, failure could allow sewage to back up into the lowest level. A non-return valve plus a high-level alarm and cut-out protects the basement and warns occupants.

Question 47Building Services

A heating system with radiators is balanced. If a radiator nearest the pump is fitted with a fully open lockshield valve while distant radiators are restricted, what is the likely result?

  1. A reduction in boiler efficiency due to lower return temperature
  2. Even temperatures throughout because the pump delivers a fixed flow
  3. The pump automatically reducing its speed to suit the load
  4. The near radiator overheating while distant ones remain cool Correct answer.

Explanation

Water follows the path of least resistance, so an unrestricted near radiator takes more than its share of flow. Distant radiators then receive less flow and stay cooler, which is why balancing restricts the near valves.

Question 48Building Services

A landlord wants to reduce legionella risk in a hot-water system serving a small block of flats. Which combination of measures best addresses the risk?

  1. Store water below 20 °C and distribute it without temperature control
  2. Remove all thermostatic mixing valves from the system
  3. Reduce the cylinder thermostat to 40 °C to save energy
  4. Store hot water at 60 °C or above and distribute so it reaches outlets hot, with regular flushing of little-used outlets Correct answer.

Explanation

Legionella multiplies in warm water, so storing hot water hot enough and keeping it hot to the outlet limits growth. Regular flushing of infrequently used outlets prevents stagnation where bacteria can multiply.

Question 49Building Services

A naturally ventilated building relies on stack effect. On a still, warm day the ventilation rate falls well below design. Which explanation best accounts for this?

  1. The internal and external temperatures are similar, so buoyancy driving pressure is small Correct answer.
  2. The wind speed is too high for the openings to cope
  3. The openings are too large for the required flow
  4. The building fabric has too low a U-value

Explanation

Stack ventilation depends on the density difference between warm internal air and cooler external air. When temperatures equalise, the driving pressure falls and so does the airflow.

Question 50Building Services

A fire door is required to protect an escape route. Which combination of features best ensures it performs its function in a fire?

  1. A self-closing device, intumescent strips and a fire-resisting glazed panel where required Correct answer.
  2. A door with a gap at the head to allow smoke to pass
  3. A hold-open device linked to the fire alarm and a plastic vision panel
  4. A standard internal door with a door closer added

Explanation

A fire door must close reliably, seal the gap against smoke and, where glazing is present, use fire-resisting glass. Hold-open devices must release automatically on alarm to be acceptable.