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Since 2002, CIBSE has been supplying the industry with the standard weather files to be used in building performance analysis using simulation tools. In collaboration with Exeter University those files have now been updated to a more recent baseline to better represent our current climate and weather patterns.

Furthermore, CIBSE, in collaboration with UK Climate Impacts Programme (UKCIP), Arup and Exeter University have also updated the future weather files based on the latest climate change projections in order to assist professionals in the use of weather and climate change information in building design and future proofing of buildings.

With the increasing demand for more sustainable and energy efficient buildings and services to combat climate change, weather data has now become an essential component of virtually every new building design and major refurbishment.

Watch the latest CIBSE Weather Data Webinar

The UK Meteorological Office (MO) collects weather data at stations across the UK. Climate variables measured at hourly intervals include air temperatures, wind speed and direction and air pressure etc. CIBSE licenses the historic weather data from the MO for 13 locations across the UK, and 3 in London. The weather variables are synthesised into 2 types of CIBSE weather files: 

- Design Summer Year (DSY)
- Test Reference Year (TRY)

DSYs and TRYs are used as climate inputs into building simulation software. TRYs files are used to do compliance analysis for UK Building Regulations:


The TRY is composed of 12 separate months of data each chosen to be the most average month from the collected data. The TRY is used for energy analysis and for compliance with the UK Building Regulations (Part L). 


The DSY is a single continuous year rather than a composite one made up from average months. The DSY is used for overheating analysis. 

The parameters included in the data sets are: dry bulb temperature (°C); wet bulb temperature (°C); atmospheric pressure (hPa); global solar irradiation (W·h/m2); diffuse solar irradiation (W·h/m2); cloud cover (oktas); wind speed (knots); wind direction (degrees clockwise from North); and Present Weather Code.

For more information download the Technical Briefing and Testing [PDF]

The packages are made up of data presented in all three formats - EDSL Tas, EPW & Excel.

Note: If your software is looking for .fwt files:  

This is the old format used in IES software. IES have now switched to using EPW files. Files in this format are included in CIBSE's 2016 weather data sets. However, as  stated elsewhere, when used for compliance purposes (and only for this purpose as Regulations have not been updated) the old TRY sets are still required, and hence the software seeks .fwt formatted files. For this reason those sets are still made available on request.  
Request more information from our team

Download and fill out the order form and email your completed form to [email protected]. After ordering, files will be supplied via a link that will be emailed after purchasing.

Download order forms:

CIBSE Members

Note: Prepayment for Weather Data sets is required before sets are made available to purchasers.

For advice on which packages to choose please phone our team on +44 (0)20 8772 3652 or email [email protected]

For details of multi-user licences, email [email protected]

View all packages [PDF]

Option 1: Current CIBSE TRY/DSY Hourly Weather Data (14 sites)
Option 2: Future CIBSE TRY/DSY Hourly Weather Data (14 sites)

Future hourly weather files, based on the existing Design Summer Years (DSYs) and Test Reference Years (TRYs) which incorporate the UKCIP09 climate change scenarios, are available for 14 sites , for three time periods (2020s (2011-2040), 2050s (2041-2070) and 2080s (2071-2100)), for the following emissions scenarios:

- 2020s – High emissions scenario – 10th, 50th, 90th percentile,
- 2050s – Medium – 10th, 50th, 90th,
- 2050s – High –  10th, 50th, 90th,
- 2080s –  Low, 10th, 50th, 90th,
- 2080s – Medium – 10th, 50th, 90th,
- 2080s – High – 10th, 50th, 90th.

Option 3: Combined current & future CIBSE TRY/DSY Hourly Weather Data (14 sites)

Purchase options 1 and 2 together and receive a discount on the individual package price.

You can purchase sites individually or all together:

CIBSE Member Price Options
Standard Price Options

Note: Prepayment for Weather Data sets is required before sets are made available to purchasers. Please see How to Order Weather Data below.

In London, the GLA requires that modelling is carried out using weather data and guidance from CIBSE 'Design Summer Years for London' (TM49: 2014). The guidance advises using weather files which account for both the UHI effect and for future climate change.

In line with this the ‘GLA Energy Planning – Greater London Authority guidance‘ (April 2015) specifies that three different weather data files should be used in overheating analysis:

- 1976: a year with a prolonged period of sustained warmth.
- 1989: a moderately warm summer (current design year for London)
- 2003: a year with a very intense single warm spell.

The TM49 dataset contains each of these weather years for three London sites (urban, suburban and rural) in order to take account of the varying UHI effect.

For buildings with long service lives or where overheating impacts are more critical, it is suggested that the building is modelled using more extreme (‘future’) weather data in addition to modelling against the three weather files above. The TM49 dataset, product code WDD16LON, includes future weather files for this purpose.

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What Is Different About The New Packages?


The TRY files have been updated to use a 30 year baseline, instead of the previous 21 years, the average months are selected from 1984 – 2013. This will ensure that the observed effects of climate change will be included in the selection of the months. 


This update of the DSY is a slightly more complex. The warm year is selected from a 30 year baseline 1984 – 2013 and the procedure for selecting the warm year has changed. The methodology for selecting the warm years is the same as that used in TM49: Probabilistic DSY for London. There are now 3 DSYs available per location, representing summers with different types of hot events:

- DSY1: Moderately warm summer 
- DSY2: Short, intense warm spell
- DSY3: Long, less intense warm spell

Note: New set WDD16LON supports TM49 Probabilistic DSY for London and is identical to the previous set WCSYL.

All the above TRYs and DSYs are also available for future time periods based on the UKCP09 climate projections.

View new packages:

- CIBSE Members

The 2016 TRYs are now requested for compliance, as outlined in the National Calculation (NCM) Modelling Guide came into force on 15 June 2022. These have a product code prefix of WCT16, suffixed by site code  - BEL for Belfast, BIR for Birmingham, CAR for Cardiff, EDI for Edinburgh, GLA for Glasgow, LEE for Leeds, LON for London*, MAN for Manchester, NEW for Newcastle, NOR for Norwich, NOT for Nottingham, PLY for Plymouth, SOU for Southampton, SWI for Swindon, and SET for the full set of all 14 sites.
* Note: The London TRY set is based on one site only, Heathrow. 

If you wish to purchase the superseded versions, please contact [email protected] or tel: +44 (0)20 8772 3618.

For more information on the methodology and use of the new DSYs for London download the free publication TM49 Design Summer Years for London.

CIBSE Weather data sets are based on data officially licensed from the UK Meteorological Office.  Further information on the Met Office’s range of services for construction can be found on their website