Rules of thumb | Archive Titles

Table 1 External conditions
Design area	Application	Other information	Rule of thumb
Winter Design temperatures for heating	Without surplus boiler capacity		-4°C
	With 20% surplus boiler capacity	Single-storey building	-3°C
		Other buildings	-1°C
	Rate of lowering outdoor design temperature with altitude above sea level		-0·6°C/100 m
Summer design temperature for air conditioning		Dry bulb temperature	28°C
		Wet bulb temperature	19°C

Table 2 Ventilation and air conditioning
Design area	Application	Other information	Rule of thumb
Ventilation: recommended maximum temp.	Offices	95% operation/year	25°C
Air conditioning: recommended maximum temp	Offices	95% operation/year	24°C (or lower)
IT rooms by classification	Type A IT rooms	Specifically designed and built for IT equipment (ideally, Isolated from office areas)	Dedicated IT room required
	Type B IT rooms	Designed for intensive use of IT equipment at workstations (where air-conditioning must be used)	Air-conditioned office, room or workspace
	Type C IT rooms	Room where IT equipment is used at workstations (may use natural or mechanical ventilation)	Non air-conditioned office, room or workspace

Table 3 Room air movement
Design area	Application	Other information	Rule of thumb
Maximum recommended mean air velocities		In winter	0·15 m/s
		In summer	0·25 m/s
		At 21°C	0·15 m/s
		At 22°C	0·20 m/s
		At 23°C	0·25 m/s
		At 24°C	0·30 m/s
		On back of neck	0·20 m/s
		Papers will lift at velocities in excess of	0·80 m/s
		Television and broadcasting studios	0·20-0·30 m/s

Table 4 Noise levels
Design area	Application	Other information	Rule of thumb
Recommended maximum background noise levels	Very quiet rooms	Concert halls, sound studios	NR 20
	Quiet rooms	Bedrooms, theatres, churches	NR 25
	Private rooms	Small offices, libraries, living rooms	NR 30
	Public rooms	General offices, classrooms, small shops	NR 35
	General areas	Reception areas, restaurants	NR 40
	Work areas	Kitchens, computer rooms, large shops	NR 45
	Industrial areas	Factories	NR 50 or above
Intelligibility of telephone conversation background noise levels		Satisfactory	Up to NR 50
		Slightly difficult	Up to NR 60
		Difficult	Up to NR 60
		Unsatisfactory	Over NR 75
External noise level criteria for new noise (above background noise)		If more than 10 dBA	Complaints expected
		If less than 5 dBA	Marginal
Limiting distances for speech intelligibility (background noise level)		Up to NR 40	7·0 m
		Up to NR 45	4·0 m
		Up to NR 50	2·2 m
		Up to NR 55	1·2 m
		Over NR 70	Too noisy

Table 5: Comfort data sheet
Building type	Internal design temperature	Infiltration	Ventilation	Lighting level	Noise level
	Summer	Winter	(ac/h)	fresh air	(Lux)	(NR)
Cinemas (sedentary role)	21-23°C	19-21°C	0·5 ac/h	8 l/s/person	300 lux	NR25 - NR30
Computer rooms (general)	21-23°C	19-21°C	1 ac/h	8 l/s/person	300 lux	NR35 - NR45
Education (teaching spaces)	21-23°C	19-21°C	2 ac/h	8 l/s/person	300 lux	NR25 - NR35
Exhibition hall/conference facilities	21-23°C	19-21°C	0.25-0.5 ac/h	8 l/s/person	300 lux	NR40
Factory/warehouse	21-23°C	11-21°C	0.25-2.5 ac/h	8 l/s/person	750-1000 lux	NR45 - NR 65
Fitness/health clubs (equipment rooms)	18°C	12-18°C	0.75 ac/h	10-12 ac/h	300 lux	NR30 - NR40
Hospitals (ward and patient areas)	23-25°C	22-24°C	2 ac/h	8 l/s/person	50 - 100 lux	NR30 – NR35
Hotels (bedrooms)	21-23°C	19-21°C	1 ac/h	8 l/s/person	50 - 100 lux	NR20 – NR30
Libraries (reading rooms)	24-25°C	22-23°C	0·25-0·75 ac/h	8 l/s/person	300 lux	NR30 – NR35
Museums and galleries (display, storage)	21-23°C	19-21°C	1 ac/h	8 l/s/person	200 lux	NR30 – NR35
Offices (general, BCO data)	24°C	22°C	0·25-0·5 ac/h	8-12 l/s/person	300-500 lux	NR25 – NR40
Retail (shops/stores)	21-23°C	19-21°C	0·5-1 ac/h	8 l/s/person	500-750 lux	NR35 – NR45
Swimming pools (pool halls)	23-26°C	23-26°C	0·5 ac/h	0-15 l/s/m² (of wetted area)	300 lux	NR40 – NR 50
While every effort has been made to establish current practice, the guide’s authors are keen to point out that the rules of thumb are merely aids to the design process.
They must not be used in place of detailed design data. The responsibility for the safe and appropriate use of this data rests with the engineer.