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Technical answers - building performance and Building Regulations and sustainable refurbishmentDecember 2012

BSRIA's John Sands provides answers to the latest technical questions posed by BSRIA members, including measuring building performance and water use in offices.

Building performance

Q. How do I conduct a post-occupancy evaluation (POE) so I can understand how my buildings are performing?

A. The initial question to consider is what is the purpose of the survey? Is it to measure and improve the performance, to compare the performance against other buildings, or to provide feedback to improve the design of future buildings?

Another aspect to consider is type of building on which the survey is going to be performed. You may need to prepare a different survey for alternative types of building, as some buildings have very different operational characteristics. Occupant surveys can be easy in offices, but more problematic in schools where staff may not have time to fill in a paper-based survey.

The Usable Buildings Trust (UBT) maintains a portfolio of POE techniques1. For example, a format for higher education facilities has been developed by AUDE, HEFCE and the University of Westminster.

Whatever methods are used to measure a building's energy consumption, it is vital to be consistent with the measurement of floor area (either gross internal or treated floor area). It is best practice to use actual or customer readings of annual electrical consumption, and to treat estimated readings with great caution. It is also important to be consistent - and explicit - about the carbon factors used to calculate the carbon dioxide emissions.

A tried and tested occupant survey method is the Building Use Studies (BUS ) system developed by Adrian Leaman and now available from both Arup (which now owns the method) and BUS. The survey was developed in the 1990s and is notable for its benchmark database. This allows the occupancy survey statistics to be benchmarked against other buildings.

If you are looking to develop a bespoke occupant survey you may want to include questions related to a variety of parameters such as temperature, air quality, comfort, lighting - both natural and electric - noise, design, and user control over environment. A ranking scale (unsatisfactory -3 to +3 very satisfied, or sometimes 1 to 7) can be used to provide statistical feedback on the performance metrics.

Note that home-grown surveys will not be able to compare results to any benchmarks, and issues of survey ethics and data confidentiality must be satisfied. It is therefore usually better to use an existing and proven survey system rather than to design your own.

Building Regulations

Q. Other than for Part L, are there any exemptions from the Building Regulations covering energy and sustainability for refurbishing listed buildings?

A. English Heritage provides advice on energy efficiency requirements which is referenced in some of the Building Regulations Approved Documents.

English Heritage suggests that factors relating to energy may be in Parts C, F, J and materials and workmanship (as well as Part L). Also to note that the same controls and exemptions apply whatever the listing grade.

Part C notes that for historic and listed buildings: "the aim should be to improve the resistance to contaminants and moisture wherever it is practically possible."

Part E states: "In the case of some historic buildings undergoing a material change of use, it may not be practical to improve the sound insulation to the standards set out…the aim should be to improve sound insulation to the extent that it is practically possible."

Part F states: "Guidance given by English Heritage and in BS 7913 Principles of the Conservation of Historic buildings should be taken into account in determining appropriate ventilation strategies for building work in historic buildings. It says: "In general, new extensions to historic or traditional dwellings should comply with the standards of ventilation as set out in this Approved Document". Part G also refers to English Heritage guidance.

Water use in offices

Q. What are typical values for water consumption in offices?

A. As part of a funded research project, CIRIA produced a simple guide to benchmarking the water consumption of offices. CIRIA W11 Key Performance Indicators for Water Use in Offices includes data on typical patterns of water consumption, with most consumption taking place in washrooms.

As well as expressing water consumption in terms of both cubic metres per employee per year (an average of 4) and litres per employee per day (an average of 16), CIRIA W11 also gives water consumption in cubic metres per square metre per year (an average of approximately 0.55) and in litres per day per square metre (an average of approximately 2.2).

The Plumbing Engineering Services Design Guide, published by the Institute of Plumbing, expresses water consumption in offices and general work places in terms of daily water demand. The guide gives figures of 45 litres per person where there is a canteen, and 40 litres per person without a canteen.

For more information about the benefits of BSRIA Membership, including technical support from our expert engineers, contact Michael Doig:

Tel: +44 (0) 1344 465532
or email

Building performance evaluation

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