Retrofitting for All Seasons: Addressing Overheating in Existing Homes
With the introduction of PAS 2035:2023 on 30th March 2025, the issue of overheating in homes has been brought to the forefront of the retrofit process. Under the updated standard, all retrofit projects must now consider and mitigate the risk of overheating caused by the installation of Energy Efficiency Measures (EEMs), to protect the comfort and well-being of occupants throughout the year.
Understanding Overheating
Overheating has been a key topic in the new build sector since changes to new build regulations in June 2022, which required all new dwellings in England to undergo an overheating risk assessment. These assessments are crucial in ensuring that new homes remain comfortable during warmer weather and do not pose health risks due to excessive internal temperatures.
Now, with PAS 2035:2023, this focus has rightly shifted to existing homes. The standard stipulates that:
“The retrofit design shall include measures to inhibit overheating of the dwelling during the installed life of the EEMs.”
Best practice guidance recommends that overheating be assessed using Approved Document O and CIBSE TM59, both of which provide in-depth methodologies for evaluating thermal performance and identifying potential problems. All Elmhurst accredited overheating assessors are qualified to produce risk assessments based on the detailed method of Part O and CIBSE TM59 for dynamic thermal modelling.
Why does Overheating matter for Retrofit projects?
Retrofitting is essential to improving energy performance in the UK’s ageing housing stock, with a significant focus on keeping homes warmer in winter through upgrades like insulation, air tightness improvements, and new heating systems. However, these same improvements can inadvertently trap heat in summer, leading to uncomfortable, or even dangerous, living conditions.
With 80% of the UK’s building stock still expected to be in use by 2050[1], the majority of which was constructed long before modern energy standards, the demand for retrofit works is rapidly increasing and with this so does the demand for competent Overheating assessors.
The Challenge of Existing Buildings: Creative Thinking Required
Unlike new build projects where designs can be optimised from the start, retrofitting involves working with existing structures, often with constraints that make traditional solutions less suitable. For instance, reducing window sizes to limit solar gains may not be possible in a retrofit scenario. This means retrofit designers and coordinators must use innovative approaches to control overheating, such as:
- Installing external shading solutions (e.g. shutters, brise-soleil)
- Using low g-value glazing to reduce solar heat gain
- Incorporating louvred windows for improved ventilation
- Ensuring ventilation in the property is adequate and removing excess heat from the property
These solutions, when applied thoughtfully, can significantly improve internal comfort without compromising the energy-saving goals of the retrofit.
The Importance of Competency in Overheating Assessments
As overheating becomes a more prominent part of the retrofit process, so too does the need for competent professionals who understand the methodology and can provide accurate assessments. Emma Grantham, New Build Team Leader and Overheating Scheme Owner at Elmhurst Energy, highlights this:
“Overheating is a critical consideration in the retrofit process, as Energy Efficiency Measures (EEMs) designed to improve thermal performance in winter can have detrimental effects during the summer months. As such, overheating assessments must be carried out by qualified professionals. Elmhurst-accredited overheating scheme members possess the necessary training and expertise to conduct these assessments effectively, ensuring accurate and reliable evaluations of thermal performance year-round.”
Elmhurst’s Overheating Competency Scheme ensures assessors are equipped with up-to-date knowledge and practical skills to deliver high-quality assessments aligned with industry standards.
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