TM52 & TM59 Overheating Analysis
For Domestic and Commercial Properties
What are CIBSE TM52 and TM59?
TM52 and TM59 are both methodologies that have been developed by CIBSE to assess, whether a building is likely to overheat. TM52 was the front runner and can therefore be used to assess the risk to any type of building, however with the later introduction of TM59 - which was specifically designed for assessing domestic properties - the methodology has been fined tuned to address the nuances particular to residential properties and the impact of external temperatures etc.
Is it compulsory to have an overheating assessment?
Generally, outside of Greater London, albeit good practice, it is not compulsory to implement either a TM52 or TM59 overheating assessment when designing and constructing new buildings. However, in London if a project is deemed to be a ‘Major Development’ then it will be a compulsory obligation as part of the planning process.
The London Plan, Policy 5.9 Overheating and Cooling states:
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‘Major development proposals should demonstrate how the design, materials, construction, and operation of the development would minimise overheating and also meet its cooling needs. New development in London should also be designed to avoid the need for energy intensive air conditioning systems as much as possible. Further details and guidance regarding overheating and cooling are outlined in the London Climate Change Adaptation Strategy’.
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A Major Development is defined in The London Plan as:
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‘For dwellings: where 10 or more are to be constructed (or if number not given, area is more than 0.5 hectares).
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For all other uses: where the floor space will be 1000 sq. metres or more (or the site area is 1 hectare or more). The site area is that directly involved in some aspect of the development. Floor space is defined as the sum of floor area within the building measured externally to the external wall faces at each level. Basement car parks, rooftop plant rooms, caretakers’ flats etc. should be included in the floor space figure’.
Why do we have to address overheating?
Overheating in a residential property can have a major effect on the health and wellbeing of the residents. Properties that overheat, at the very least, provide an uncomfortable environment in which to live and at the worst can result in the residents suffering from stress, sleep deprivation and for those more vulnerable habitants, through heat waves or extreme hot weather, early deaths. The Committee on Climate Change has estimated that mortality rates arising from overheating could rise from 2000 per year in 2015 to 7000 per year by the 2050s. {1} So, unless overheating is considered and mitigating solutions are found, at the design stage, the situation looks likely to get worse.
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The risks of overheating also need to be considered when designing commercial buildings, it is paramount to the end user that the working environment is comfortable. People who are uncomfortable or dissatisfied with their working thermal environment, may be affected by ill health and/or their ability to perform effectively may be compromised, the consequence of which is a cost to both the individual and the organisation who occupies the building.
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Equally buildings that overheat will often result in increased fuel bills, particularly in buildings that have air conditioning, mechanical ventilation or comfort cooling fitted as occupants will invariably mitigate the effects of the overheating by employing the use of these systems to create a more comfortable environment.
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{1) 1 - Hajat et al. (2013) Climate change effects on human health: projections of temperature-related mortality for the UK during the 2020s, 2050s and 2080s. Journal of Epidemiology and Community Health 10.1136/jech-2013-202449.