Planning to Tackle Overheating Upfront

22 Jul 2019

Tom de Saulles, Building Physicist, The Concrete Centre discusses the new planning tool to inform planners about early considerations for overheating.

At least seven people were killed in the heatwave that swept across mainland Europe in late June, with France being worst hit, recording its highest ever temperature of 45.9°C. It’s no surprise then that the issue of overheating is becoming ever present in the minds of designers and architects.

It has also been recently identified by the Good Homes Alliance (GHA) as an issue that needs consideration at the planning stage, as initial decisions can have long term consequences. With this in mind, GHA have developed a new tool to help planners and design teams identify and mitigate the risk of overheating in housing developments at an early stage.

The GHA tool basically consists of a scoresheet containing 14 questions aimed at identifying any overheating risk or mitigation factors specific to a housing project. The resulting score indicates high, medium or low risk. The challenge in producing such a tool lies in achieving the difficult balance between simplicity in use and accuracy in evaluating risk.

Whilst the tool is not meant to provide a detailed assessment, results may carry weight in primary design decisions and, in this respect, there is an important issue where use of the tool could potentially give an over-simplistic and skewed outcome. This relates to the treatment of the building fabric and the role thermal mass can play in reducing overheating risk.

As you would expect, the use of thermal mass is included as one of the measures for reducing risk. Unfortunately, the tool limits its benefit to a one degree reduction internal temperature; significantly less than that apportioned in the SAP overheating assessment produced by BRE, which awards up to a 3.5 degree reduction for using thermal mass. Only apportioning a one-degree reduction, also seems contrary to the multitude of design guidance produced over the years, highlighting the notable benefit thermal mass provides when actively used to help maintain summertime comfort.

For example, research recently commissioned by the Committee on Climate Change shows that the combination of thermal mass and night cooling can reduce overheating by 60-80% depending on dwelling type.1
The Concrete Centre is pleased to have supported and contributed to the GHA project that has produced this valuable resource for planners and the wider design team. Overall, the tool is a welcome addition that should raise awareness about overheating and may help avoid high risk designs at project inception.

However, early design decisions can impact negatively unless well informed and joined up with the complicated set of parameters that contribute to creating a successful built environment. Users should be mindful of its limitations, particularly in respect of how it downplays the difference in overheating performance between light and heavyweight construction, due to the thermal mass of the building fabric.

Now more than ever, we need to be applying all the practical, low cost measures available to help ensure long term resilience to climate change in new dwellings. Of all the adaptation measures, the fabric, along with a dwelling’s form and orientation, are the most fundamental to get right at the planning stage as these can’t be retrofitted later. and give additional wins of reduced energy bills, improved health and less electricity demand.

Whilst the tool is not meant to provide a detailed assessment, results may carry weight in primary design decisions and, in this respect, there is an important issue where use of the tool needs particular care.

The Concrete Centre offers simple guidance on understanding how thermal mass works and can provide assistance to inform a more detailed assessment of overheating in housing.

1 Committee on Climate Change, Updating an assessment of the costs and benefits of low-regret climate change adaptation options in the residential buildings sector, Final Report, REF GH/07-18

Written by - Tom de Saulles, building physicist at The Concrete Centre