UK: The growing problem of overheating in homes is tackled in new guidance from the Chartered Institution of Building Services Engineers (CIBSE).

As the UK enters a summer that could be the hottest since 1976, and with estimates that heat-related mortality rates could rise from 2,000 per year in 2015 to 7,000 per year by the 2050s, CIBSE has sought to address what the industry had identified as a gap in its knowledge.

The new Technical Memorandum 59: Design methodology for the assessment of overheating risk in homes (TM59) – available now as a free download – attempts to set a standard by which overheating can be assessed using a consistent methodology.

According to CIBSE, input assumptions regarding the occupancy profiles, internal gains, natural ventilation capabilities, etc, in the design process will 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 consultants will now be using the same assumptions regarding the use of the properties when assessing overheating risk.

“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,” explained CIBSE research manager Dr Anastasia Mylona.

“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.”

Overheating risk is also affecting existing homes, especially in buildings that do not have adequate methods for dissipating heat gains and are less resilient to climate change. The health and wellbeing impacts of overheating can be significant for residents, resulting in stress, anxiety, sleep deprivation and even early deaths in heat waves, especially for vulnerable occupants. The situation is predicted to get worse.

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.

Uniquely, TM59 draws on CIBSE’s own weather data products, developed with the support of the Met Office, which play a fundamental 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, this data is combined with the latest climate change projections to produce future weather files up to the 2080s.

TM59 is said to have 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.

TM59 can be accessed and downloaded here.