The limits of thermal comfort: avoiding overheating in European buildings

Overheating has become a key problem for building design. The need to reduce energy consumption whilst dealing with global climate change has reduced the options available for building comfortable, low-energy buildings. Research has been directed towards methods for increasing indoor winter temperatures but this can lead to lightweight, highly insulated buildings that respond poorly in the summer. CIBSE has responded by forming the Overheating Task Force.The Task Force realised that one problem for designers has been the absence of an adequate definition of overheating in naturally ventilated buildings. In the past overheating has been defined as a number of hours over a particular temperature, irrespective of conditions outside the building. Recent work embodied in European standards suggests that the temperature that occupants will find uncomfortable changes with the outdoor conditions in a predictable way. This research informs the CIBSE guidance presented in this Technical Memorandum. The meaning of the research and the link with overheating are explained and a series of criteria by which the risk of overheating can be assessed or identified are suggested.More detailed information about using simulation to predict the danger of overheating is available in CIBSE Guide A (CIBSE, 2006/2013). CIBSE KS16: How to manage overheating in buildings (2010) gives information directed at building managers and owners about the cause of overheating and some practical suggestions for avoiding or mitigating it.