HEATING, VENTILATION & SERVICES 47
Ventilation: the key to solving the Part O overheating challenge
New-build homes are more energy effi cient, as a result are prone to overheat. Steve Pearce of Vent-Axia explores how architects can use smart ventilation strategies to combat this, and support the 2050 net zero goal.
T
raditionally, UK homes did not struggle with overheating. Older buildings, often constructed from
heavyweight materials, benefi ted from high thermal mass, as well as featuring relatively high air leakage rates, and low levels of thermal insulation, while large openable windows provided natural ventilation, which all helped to lower temperatures. However, today’s new build homes are far more airtight with high levels of insulation, larger areas of glazing, low-emissivity glazing, and minimal solar shading, which all contribute to overheating risks. Additionally, there are often only a limited number of openable windows, whether due to noise, air pollution, or security considerations. Meanwhile, opportunities for overnight cooling, through either natural or mechanical night-time purge ventilation, are frequently insuffi cient. The risk of overheating is further intensifi ed by climate change, which has led to warmer summers. Meanwhile, urbanisation has also raised temperatures, especially in city centres like London, where the urban heat island effect can elevate nighttime temperatures by 10°C compared to its surrounding rural areas. As a result, occupants in some new homes are now experiencing indoor temperatures that exceed comfort, and in some cases pose health risks.
Architectural measures Ventilation can be an important part of the solution for overheating. However, there are a number of architectural measures that can be taken fi rst to mitigate internal temperatures. A few proactive approaches
ADF MAY 2025
architects can take include altering a building’s orientation to reduce solar gain; reducing glazed areas; and specifying low g-value windows that manage heat ingress, while maintaining SAP compliance. Meanwhile, maximising external shading, whether from balconies, overhangs or recessed windows have the ability to signifi cantly cut solar gain.
Increasing wall and roof insulation to minimise conduction gains; managing the heat with exposed internal thermal mass and high ceilings; and using green roof systems, can all help regulate internal temperatures. In addition, to minimise the heat generated in a home, communal heating pipework can be rerouted or insulated, especially in corridors. The next step for architects to consider is how excess heat can be removed by maximising natural ventilation through large windows; maximising cross-fl ow ventilation and adding ventilation louvres in walls, and employing purge ventilation at an elevated rate. However, architects can face some obstacles. For example, openable windows are not always viable, Park K (protection from falls), Part M (security), high levels of air pollution, and environmental noise can all restrict the use of windows for ventilation.
Guidance
Recognising the seriousness of the overheating problem, the Government introduced Approved Document O of the Building Regulations in 2021. Part O specifi cally addresses the challenge of overheating in new dwellings, care homes, and student accommodation.
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Overheating is a serious health issue, but it is also an issue of comfort
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