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Technical FAQs

What is the maximum permitted temperature in an office? 

There is no statutory limit to the upper temperature in workplaces. The Workplace (Health, Safety and Welfare) Regulations 1992 (Statutory Instrument 1992 No, 3004) require only that: 'During working hours, the temperature in all workplaces inside the building shall be reasonable.' Section 1 (Environmental criteria for design) of CIBSE Guide A: Environmental design, suggests for offices that the temperature range for comfort should be 21-23ºC in winter and 22-24 ºC in summer. The latter range applies to air conditioned buildings. Higher temperatures may be acceptable in non-air conditioned buildings.

Is 'category 2' lighting a legal requirement in offices? 

No. The Schedule to the Workplace (Display Screen Equipment) Regulations 1992 (Statutory Instrument 1992 No. 2792) requires that: 'Any room lighting or task lighting provided shall ensure satisfactory lighting conditions and an appropriate contrast between the screen and the background environment, taking into account the type of work and the vision requirements of the operator or user.' The term 'category 2' is no longer used by the CIBSE. It was used to describe a particular design of luminaire (light fitting) that could be employed to prevent reflections of the luminaire on the display screen. Unfortunately, in doing so, these luminaires can produce a gloomy environment if used on their own without consideration of surface reflectances. In most offices, particularly where modern computers with bright screens are used, such reflections are not likely to occur and therefore it is not necessary to specify this type of luminaire. CIBSE Lighting Guide LG3: The visual environment for display screen use and its 2001 addendum gives detailed guidance on the design of lighting schemes that will satisfy the legal requirements while providing a pleasing visual environment. For more information go to the Society of Light and Lighting's Free Downloads. It should be noted that the provisions of the Regulations cover many other aspects of computer equipment and workstations, including the screen, keyboard, desk and operator's chair. The schedule to the Regulations may be found on the HMSO website

What is the legal status of CIBSE publications? 

CIBSE publications are intended as guidance only. They have no legal standing in themselves. However, there may be a contractual obligation to follow CIBSE publications if cited within project contracts. Also, as the published guidance of an authoritative body, CIBSE publications are often used as evidence in litigation.

What is the recommended lighting level for offices? 

The CIBSE Code for Lighting recommends a maintained illuminance of 500 lux for general offices (e.g. writing, typing, reading, data processing, etc.) and for CAD work stations and conference/meetings rooms. Where the main task is less demanding, e.g. filing, a lower level of 300 lux is recommended.

What is the 'safe' water storage temperature to avoid Legionnaires' disease? 

For hot water storage, CIBSE TM13: Minimising the risk of Legionnaires' disease offers the following guidance: 'the storage temperature, controlled from a thermostat, should be 60 °C. The distribution pipework design should enable water to reach all outlets at 50 °C within 1 minute of turning on the tap. The risk of scalding is small for most persons at 50 °C but rises rapidly above 55 °C. Caution is needed to prevent higher temperatures at the tap, and warning notices should be posted at known problem areas.'

Where can I find Approved Document L2? 

Building Regulations Approved Documents can be downloaded free-of-charge from the Planning Portal website at The website contains deatils of consultations of proposed revisions to approved documents. Printed copies may be purchased from The Stationery Office, now known as 'TSO'. Their main office is TSO, PO Box 29, Norwich NR3 1GN (fax orders: 0870 600 5533; telephone orders/enquiries: 0870 600 5522; e-mail orders: TSO also has an excellent website at

Why have the tables for simultaneous demand calculations disappeared from the CIBSE Guide?

Prior to publication of CIBSE Guide G: Public health engineering, there were (at least) three different methods for simultaneous demand calculations. These were published in CIBSE Guide B4 (1986), the Institute of Plumbing's (Plumbing engineering services design guide) and BS 6700: Specification for design, installation, testing and maintenance of services supplying water for domestic use within buildings and their curtilages. Since the three methods gave different results, the decision was taken to withdraw the 'CIBSE method' and recommend the use of BS 6700 for simultaneous demand calculations.

What is the latest version of BS xxxx? 

The best way of checking the currency of a particular British Standard is through the BSI's excellent website at

What is a 'SAP' rating? 

'SAP' stands for 'Standard Assessment Procedure'. The SAP is the Government's recommended system for energy rating of dwellings. The Standard Assessment Procedure is used for calculating the SAP rating, on a scale from 1 to 120, based on the annual energy costs for space and water heating and for calculating the Carbon Index, on a scale of 0.0 to 10.0, based on the annual CO2emissions associated with space and water heating. The SAP rating is used to fulfil requirements of the Building Regulations to notify and display an energy rating in new dwellings. Full details are given in the SAP manual, which may be downloaded free-of-charge from

What is the recommended ventilation rate for offices? 

For offices where there is no smoking, CIBSE Guides A: "Environmental Design" (2006) recommends an outdoor air supply rate of 10 litres/second per person. Spaces in which smoking is permitted should be regarded as 'smoking rooms' and an outdoor air supply rate of 45 litres/s per person is suggested for such rooms. However, it should be noted that this recommendation aims only to reduce discomfort and does not ensure health protection.

What is the status of CIBSE recommendations on hospital lighting? 

CIBSE Lighting Guide 2: Hospitals and health care buildings is available to buy in print or pdf format from the Knowledge Portal website (click here). A revised edition is in preparation; the timescale for publication will depend on the refereeing process. The general guidance in Lighting Guide 2 is still valid, but the illuminance and certain other recommendations have been superseded by information in BSEN 12464-1 Light and lighting. Lighting of work places. Part 1: Indoor work places (2002).

What are the legal requirements for office lighting? Is there a legal requirement for daylight? 

The only legal requirements are 'sufficient and suitable' and similar wording in health and safety legislation. There is no absolute legal requirement for daylight, but it is a requirement that it be provided if practicable. Various HSE guidance documents suggest good practice, but are not themselves mandatory.

Where can I obtain degree-day data? 

Degree-day data for the UK used to be published in the CIBSE journal and other magazines. This ended when the Department of Energy was wound-up some years ago. Some sources of degree-day data, though, may be found at:

For further reading, there is also a CIBSE publication TM41: Degree-Days Theory and Applicationwhich gives guidance on the use of degree-days and additional background theory.