Warmer temperatures and improved construction are leading to overheating problems in homes. Ken Sharpe, editor of “Modern Building Services”, examines new guidance from CIBSE that aims to address this vital issue.

Temperatures earlier this summer hit the heights not seen since the sizzling summer of 1976. The hot spell may seem a dim, distant memory in the middle of the school holidays, yet overheating in homes is a crucial issue facing the building-services sector. Energy-efficiency upgrades to buildings, increasing air tightness and warmer temperatures from climate change are leading to a perfect storm, particularly in care homes where the elderly are extremely vulnerable.

With the Met Office reporting that the eight warmest years in the UK since 1910 have occurred in the last 14 years, it’s timely that new guidance published by the Chartered Institution of Building Services Engineers (CIBSE) aims to tackle the issue of overheating in homes. Addressing what the industry has identified as a gap in its knowledge, CIBSE has created the new Technical Memorandum 59: Design methodology for the assessment of overheating risk in homes (TM59) in order to set a standard by which overheating can be assessed using a consistent methodology.

The new TM59, available now as a free download and officially launched at University College London on 28 June, has created a common approach to assessing risk of overheating. Input assumptions in the design process, such as occupancy profiles, internal gains, natural-ventilation capabilities and so on, can produce a wide variety of results and sometimes even mask the magnitude of overheating risk in some properties. TM59 aims to provide consistency across the industry as all CIBSE members will now be using the same assumptions when assessing overheating risk.

CIBSE is planning to back up the results of the methodology through further research and testing as it is applied in the years to come.

MBS Ken Sharpe2 Ken Sharpe Editor of Modern Building Services

Dr Anastasia Mylona, research manager at CIBSE, said: “CIBSE has created this methodology in response to growing concern in the construction industry that rising temperatures and a changing urban landscape are creating a generation of homes destined to overheat.

By creating an industry-agreed standard methodology for assessing overheating, we aim to enable designers and engineers to work together to create buildings that are more resilient to hot weather events.”

TM59 draws upon existing guidance produced by CIBSE and others on various aspects of a building’s performance to give a prescriptive approach to modelling, which will allow the methodology to be consistently applied. It also includes reporting requirements to ensure that stakeholders understand the methodology’s impact on the design.

The guide references CIBSE’s own weather-data products, developed with the support of the Met Office, which play a key role in assessing whether a particular design is likely to overheat. The datasets are based on historical data collected from 14 sites around the UK since the early 1980s. In the current version, data are combined with the latest climate change projections to produce future weather files up to the 2080s.

TM59 has been extensively ‘live tested’ on existing projects and shown to be effective, but CIBSE is planning to back up the results of the methodology through further research and testing as it is applied in the  years to come. This will allow the methodology to be refined in response to new data and user feedback.