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Weather data (1)

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, these files have now been updated to a more recent baseline to better represent our current climate and weather patterns.

In collaboration with UK Climate Impacts Programme (UKCIP), Arup and Exeter University, CIBSE has 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.

CIBSE Weather Data

CIBSE Weather Data Webinar

(23rd February 2017)


What Is Weather Data?

The UK Meteorological Office (Met Office) 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 Met Office for 16 locations across the UK, three of which are in London The weather variables are synthesised into two 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. TRY files are used to do compliance analysis for UK Building Regulations:


The TRY is composed of 12 separate months of data, each representing an 'average' month as derived from the collected data. The TRY is used for energy analysis and for compliance with the UK Building Regulations (Part L). 


The DSY represents a single continuous year, rather than a composite year made up of 'average' monthly values, and 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)
  • present weather code.

For more information, download the Technical Briefing and Testing PDF

The packages are made up of data presented in three formats:

  • EDSL Tas
  • EPW
  • Microsoft Excel. 

If your software is looking for .fwt files: this is the old IES format; IES now uses .epw files. CIBSE's 2016 weather data sets do include .fwt files. Request more information from our team

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 are based on the existing design summer years (DSYs) and test reference years (TRYs), and incorporate the UKCIP09 climate change scenarios. These are available for 14 sites over three time periods and emissions scenarios:

  • 2020s (2011-2040)
    • High - 10th, 50th, 90th percentile
  • 2050s (2041-2070)
    • High - 10th, 50th, 90th percentile
    • Medium - 10th, 50th, 90th percentile
  • 2080s (2071-2100)
    • High - 10th, 50th, 90th percentile
    • Medium - 10th, 50th, 90th percentile
    • Low - 10th, 50th, 90th percentile.

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

A discount is available when Options 1 and 2 are purchased together.

View all CIBSE weather data packages [PDF]

See all pricing options here:

In London, the GLA requires that modelling is carried out using weather data and guidance from CIBSE TM49 Design summer years for London (2014), using weather files that account for both the urban heat island 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 variance in the urban heat island 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. Request more information from our team

What is different about the new packages?


In order to ensure that the observed effects of climate change are included in the data provided, the newer TRY files are based on data collected over the 30 years from 1984 to 2013. (The previous TRY files were based on a dataset covering a 21-year period.) 


The update of the DSY files was a slightly more complex: the warm year is selected from the 30-year baseline (1984–2013), but the procedure for selecting the warm year has changed - it is based on the methodology laid out in CIBSE TM49, Probabalistic DSY for London. There are now three DSYs available for each location, representing summers with different types of hot events:

  • DSY1: moderately warm summer 
  • DSY2: short, intense warm spell
  • DSY3: long, less intense warm spell

The new set WDD16LON supports the TM49 methodology, and is identical to the previous set WCSYL.

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

Building Regulations Compliance

As of June 2022, the Department for Levelling Up, Housing and Communities has officially endorsed the newer TRY weather sets (the 2016 files) for compliance. 

View new packages:

To order weather data, please email a completed order form to [email protected]. Once payment has been processed, you will be emailed a link to all files. If you are a CIBSE Member, please complete the CIBSE Members form; if you are not a member, please complete the Standard form. 

For advice on which packages to choose, please email [email protected] or call +44 (0)20 8772 3652.

CIBSE TM49For more information on the methodology and use of the new DSYs for London download the free publication TM49 Design Summer Years for London.


Met OfficeCIBSE 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