Building thermal modelling - also known as thermal comfort modelling or overheating assessment - is a form of analysis designed to assess the thermal comfort of buildings and mitigate any overheating risks. There are two standardised approaches: CIBSE TM52 for non-residential buildings, and TM59 for residential buildings (TM simply means ‘Technical Memorandum’).

Modern construction techniques generally deliver buildings with high levels of thermal insulation and good airtightness. However, summer overheating can be a significant risk - and will become more so as we deal with the consequences of a warming climate. Thermal comfort models will therefore only become more important in order to ensure buildings are healthy and safe places to be.

Why is a thermal comfort model required?

Building designs often focus on headline performance metrics, especially those that form part of national building regulations. It can be easy to assume that achieving energy efficiency compliance through SAP calculations and SBEM calculations will lead to a comfortable building for occupants.

That is not always the case, however.

For example, a building designed to maximise winter solar gains through south facing glazing may not have sufficient shading to restrict the extent of solar gains in summer, leading to uncomfortable (and potentially dangerous) increases in internal temperature.

Overheating can also occur due to something as simple as a window not being opened (perhaps because of a noisy road or a smelly bin store outside), or because the ventilation provision to the building is inadequate.

Where overheating occurs, especially in commercial buildings, it can lead to increased energy use and resource consumption through using desktop fans or even retrofitting air conditioning units - all of which serves to drive up the energy use and carbon emissions of the building even more, counter to our climate change goals.

As the issue becomes better understood, the requirement to carry out building thermal modelling becomes more widespread. Local planning authorities may request thermal comfort models as a condition of planning approvals, while the London Plan requires them in order to protect people in the capital from the risks of climate change. Analyses can also help to gain credits in BREEAM assessments.

When is building thermal modelling carried out?

Thermal comfort models are typically carried out at detailed design stage, whether to address a planning condition that needs to be discharged or to meet BREEAM or London Plan requirements.

The modelling exercise takes into account the size, shape and orientation of the building; the energy efficiency of the building fabric and glazed elements; how the building is ventilated; mechanical services, including heating and/or cooling; and how the building will be used.

As specialists in sustainable construction, Darren Evans can work with you from the earliest stages of a project. We can use our experience to help guide your design decisions so that they have a positive impact on assessments, like thermal comfort modelling, that are carried out later on. In doing so, we can help you to avoid costly and unforeseen changes that may only come to light after planning approval has been granted.

You can contact us to start a conversation and discuss the needs of your project, or find out more about the range of consultancy services that we offer to enhance the sustainability of your buildings.

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