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TM49 Design summer years for London (2014) (pdf)
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TM49 Design summer years for London (2014) (pdf)

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CIBSE Design Summer Year (DSY) for London is the most appropriate year of weather data to assess the summertime cooling needs of buildings in London.

The new CIBSE guidance TM49 and the accompanied Design Summer Years for London enable designers to analyse the summer performance of their buildings and investigate the impact of urban macroclimatic factors and climate change when carrying out overheating risk assessments for buildings in London.

Urban centres, especially in the south and south east of the UK, will experience more intense and frequent summer hot events, exacerbated by the urban heat island (UHI) effect. The UHI effect is a result of the dense built up of urban centres and the lack of green areas and manifests as a temperature difference between the urban centres and their rural surroundings. The TM49 Design Summer Years for London and the accompanied datasets for building thermal simulation, introduce the concept of incorporating the UHI effect and the severity of hot events in the design of buildings. Specifically, instead of having a single DSY for London (using observed data from Heathrow), three DSYs are now available capturing the local climate in three different London sites (urban, semi-urban, and rural) and for three years of varying severity of hot events.

Designing just for present weather conditions will leave buildings vulnerable to changes in climate. The availability of future climate projections helps in identifying the impacts that a changing climate will have on building performance and building vulnerabilities to future weather events. The currently available UK Climate Projections (UKCP09), released by DEFRA in 2009, are probabilistic in nature, to better quantify the climate uncertainty. This probabilistic nature encourages the better understanding of future risks when adapting to a changing climate. Future DSYs for London are also available to reflect the UKCP09 climate projections and allow designers to increase the resilience of their buildings to future changes in climate.


This new dataset - Product Code WCSYL (renamed as WDD16LON in March 2016) - comprises files in TAS, EPW and Excel formats. This can be ordered by contacting CIBSE, by telephone on +44 (0)20 8772 3618 or email [email protected].


Note: The Greater London Authority (GLA) has published guidance on preparing energy assessments - 'GLA Energy Planning - Greater London Authority guidance' (April 2015) that makes strong reference to TM49, making it a requirement that, where dynamic modelling is carried out, it should be undertaken in accordance with the guidance and data sets in TM49, which are then summarised (see paragraphs 11.9-11.12).

The GLA guidance explains the need to take the urban heat island effect in the locality of the development to be taken into account. The GLA also directs readers towards CIBSE TM52 Limits of Thermal Comfort: Avoiding Overheating in European Buildings’ as it contains "additional guidance on the limits of thermal comfort."

The GLA title can be accessed from here


Executive summary

1 Introduction

2 The Probabilistic Design Summer Years

2.1 The CIBSE Design Summer Year

2.2 Reference conceptual building

2.3 Metrics of summer warmth

2.4 Analysis of London Heathrow temperature data

2.5 Estimate of return periods for warm summers

2.6 Selection of the probabilistic Design Summer Years

2.7 Climate change projections for London and implications for the pDSYs

3 London’s urban heat island: additional weather sites

3.1 Daily minimum and maximum temperatures

3.2 Selection of rural and urban sites

3.3 Relationship between UHI intensity and warm weather

3.4 Differences in hourly data values between rural, peri-urban and urban sites

4 Conclusions

Appendix A1: Methodology of weather file generation

Appendix A2: London weather data sites — data availability

Principal author: Jake Hacker (Arup)

Contributing authors: Stephen Belcher (University of Reading); Andrew White (Arup)

Other acknowledgements: Steven Downie, Michael Holmes, Ruth Shilston, Rob Slater (Arup); Phil Jones, Clare Goodess, Colin Harpham, David Lister (University of East Anglia); Glen McGregor (formerly of King’s College London, now at the University of Auckland); Simon Gosling (formerly of King’s College London, now at Nottingham University); Fergus Nicol (London MetropolitanUniversity); Mark Gilby (Parsons Brinkerhoff); Chris Kilsby (Newcastle University); Anastasia Mylona (CIBSE); Alex Nickson (Greater London Authority); Tariq Muneer, Haroon Junaidi (Napier University).

Thanks to: Professor Michael Davies; Professor Maria Kolokotroni; Brian Spires; Elinor Huggett

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