Hot and bothered about overheating

With UK building stock facing an overheating issue, Phil Brown, European regulatory marketing manager at Pilkington UK, outlines the measures being taken to alleviate the problem.

Every winter, the UK’s abundance of draughty homes and the reality of fuel poverty exposes the vulnerable to the serious health risks that come with cold weather, including respiratory and heart diseases.

The health risks associated with homes overheating in warmer months are less widely known, however. As our building stock becomes more airtight and better insulated, hot homes in the summer could soon become more of a health threat than cold homes in the winter.

The issue, which glazing can be a contributor to, can have minor to fatal consequences, from sleep disruption harming productivity to dehydration and severe heat stroke. Recent research by Loughborough University published in the Building Research and Information Journal outlined how deaths related to overheating could triple by 2040.

Operators across the built environment are beginning to make recommendations on how Building Regulations should be revised to help alleviate the issue of overheating.

However, the glass and glazing sector specifically has a task in educating specifiers, from local authorities and architects to facilities managers, on how glazing can be used to help curb this effect – and minimise the associated health risks.

There are a wide range of factors that both contribute towards and exacerbate overheating, including rising external temperatures, increased internal gains and better-insulated, airtight properties. Furthermore, cities and towns can experience an urban heat island effect, which occurs when the harder, darker surfaces in urban areas result in warmer temperatures than rural areas.

Of greater interest to our sector, the use of glass in the building envelope can lead to overheating, too, if solar gains are excessive. For example, having large glazed windows may create a greenhouse effect during the summer period, if care isn’t taken to limit heat gain by using high performance products or considering the glazing’s orientation.

While overheating has been a consideration in the design of new homes for decades, it has been at a very basic level.

Building Regulations require that a SAP (Standard Assessment Procedure) calculation, the methodology for determining the energy performance of new homes in the UK, is submitted before building work starts.

To limit the effects of heat gains in summer, SAP contains a procedure enabling designers to assess the risk of overheating. Many consider this approach increasingly inadequate, as the provision can be met as long as the assessment indicates that a building is not a ‘high’ risk of experiencing high internal temperatures.

Given the abundance of factors that can contribute towards the issue, the SAP Industry Forum is now considering how the methodology can be revised to more accurately evaluate the risk of overheating in the future. Meanwhile, the 2020 revision of Part L, the set of Building Regulations concerning conservation of fuel and power, is also expected to have an increased focus on overheating, too, with a public consultation anticipated later this year.

Given orientation can be a major factor in causing or preventing homes from overheating, more consideration to the g-value of glazing products – the total amount of the sun’s energy transmitted through the glass – should be paid by operators in the built environment to alleviate overheating.

In the UK, the south and west elevations of a house may need to use shading due to exposure to the sun. Glass with a lower g-value (which indicates better solar control performance) can be used here to prevent heat gain in rooms, particularly if large windows are used.

Some housebuilders tend to use the same glass specification on each elevation. However, given the different levels of solar radiation each side of the house gets, it’s important to specify the right glazing on the right elevation, whether thermal performance or solar control, to help control the climate of the building.

To successfully reduce the issue of overheating in homes, the glass and glazing industry needs to educate clients on how glass can be a solution, not just a cause.

Developers in parts of Europe are already specifying solar control glass in residential projects. However, the UK remains behind the curve in this area.

Looking ahead, advanced technologies like dynamic and switchable glazing, which can react to daylight exposure and limit heat transmittance, may also provide a solution for homes in the long term. Incorporating these and other technologies into SAP is also under consideration by the industry forum.

For now, it’s clear that a greater focus on overheating within Building Regulations, and better awareness of the causes and solutions of the issue, will be paramount in tackling the growing health risk of hot homes in the summer.