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New National Modelling Guide requires update to latest CIBSE Weather Data Sets
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New National Modelling Guide requires update to latest CIBSE Weather Data Sets

30 Jun 22

The National Calculation (NCM) Modelling Guide came into force on 15 June 2022. It includes several important changes, including an upgrade to the 2016 CIBSE Test Reference Year (TRY) weather data sets.

This NCM Modelling Guide was developed in support of the 2021 Edition of the Approved Document L - Conservation of fuel and power, Volume 2: Buildings other than dwellings. It includes a number of changes in the technical requirements of software.

The latest NCM Modelling Guide provides guidance on the government’s Simplified Building Energy Model (SBEM) and other approved software tools comprising the NCM when demonstrating compliance with CO2 emissions and primary energy requirements, and calculating asset ratings as part of Energy Performance Certificates (EPCs) for buildings other than dwellings.

Along with the use of the 2016 CIBSE Weather Data files, Dynamic Simulation Model software must also meet or exceed the classification of dynamic modelling under CIBSE AM11: Building performance modelling. Additionally, the new guidance refers to CIBSE Guide A: Environmental design.

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.

You can find out more about CIBSE Weather Data sets, along with information about purchasing data packages via

Find out more about the latest NCM Modelling Guide via

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