Modern Construction and Overheating

10 Sep 2018

We have all experienced one of the hottest summers that the UK has had since 1977 and in its recently published report ‘Heatwaves: adapting to climate change’, the Environmental Audit Committee has called for tougher rules to ensure homes can deal with extreme heat.

"The Environmental Audit Committee warns of 7,000 heat-related deaths every year in the UK by 2050 and also complains about a lack of regulation to prevent overheating in buildings” say representatives from Modern Masonry.

As homes become more highly insulated, it is less easy for unwanted heat to escape during the summer months, resulting in a greater risk of overheating; a problem that is further compounded by a warming climate.

Alongside adequate ventilation and shading, the thermal mass provided by concrete and masonry construction offers another means of tackling overheating. Concrete and masonry’s thermal mass allows it to absorb and later release excess heat, helping smooth out the gains and stabilise the internal temperature. Heat stored in concrete and masonry is expelled at the end of the day by ventilating the building with cool night air. The combined benefit of thermal mass and night ventilation is accounted for in the SAP overheating check, which allows a reduction in the peak internal temperature of up to 3.5°C compared to an equivalent lightweight dwelling with night ventilation.

Overheating in homes is increasing for two key reasons:
1. Summertime temperatures are gradually rising as our climate continues to warm. 2015 was the warmest year on record and the Met Office is predicting a temperature increase of around 3°C in the south of England over the 21st century.
2. There is a greater tendency for modern, highly insulated and airtight homes to overheat as heat is more easily trapped.

The use of thermal mass has become well established and is one of a number of good practice design techniques that can be employed to reduce the growing risk of overheating. Its use ranks highly in the London Plan hierarchy of overheating measures, which designers and architects should apply to new buildings.
When it comes to modern construction, modern masonry homes can be designed to minimise the risk of overheating by deploying the thermal mass and other design measures whilst also delivering the highest levels of energy efficiency for heating in winter.

Factory production or offsite construction does not in itself result in a greater risk of overheating.  Concrete offsite solutions will have thermal mass, and this can be used with other design measures to reduce peak temperatures and likelihood of overheating.  Conversely most timber and steel offsite solutions have low thermal mass and hence can only draw on the other measures in the hierarchy and are therefore more likely to overheat.

Tom de Saulles, Building Physicist at The Concrete Centre offers his view:
“As you would expect, the masonry and concrete sector has for many years highlighted the role of thermal mass in helping address overheating in homes and the dangers of lightweight construction. Numerous organisations have also published design guidance on overheating that acknowledges the role thermal mass can play in helping tackle the issue. The collective understanding of all these organisations underpins the masonry and concrete sector’s messaging on thermal mass.  Some examples of these reports and design guidance are:

• CIBSE TM60: Good practice in the design of homes, 2018
• The London Plan – cooling hierarchy, 2016
• Zero Carbon Hub: Overheating in Homes – The Big Picture, 2015
• Zero Carbon Hub: Solutions to Overheating in Homes, 2016
• Building Research Establishment - Overheating in dwellings – guidance document, 2016
• Good Homes Alliance: Preventing overheating, 2014
• NHBC Foundation: Understanding overheating – where to start, 2012
• Technology Strategy Board: Design for future climate, 2008
• Energy Savings Trust – energy efficiency best practice in housing – reducing overheating a designer’s guide, 2005
• Faber Maunsell: Control of overheating in future housing – design guidance for low energy strategies, 2003”
Guidance on thermal mass and how to use it can be found in Thermal Mass Explained, a publication available at
Technical information on Part L1A/SAP and the use of thermal mass in concrete and masonry housing is included in: Thermal Performance Part L1A 2013 available at
Read the Environmental Audit Committee (EAC) Heat Inquiry on