Why solar-control glass should be part of the UK’s overheating debate

June’s heatwaves have exposed just how ill-equipped many of our buildings are to keep people cool as temperatures rise. As record temperatures were hit on consecutive days, it came as no surprise to most people that our homes aren’t equipped to handle the intense heat that is becoming increasingly common.

With such heatwaves there comes a potential health risk from overheating, which can lead to issues such as dehydration and heat stroke. It is no wonder then that Building Regulations are having to shift to match these warmer times.

The introduction of Part O of the England and Wales Building Regulations now mandates design strategies to limit unwanted summer solar heat and ensure adequate ventilation to help remove excess indoor heat. Overheating is now a design and compliance issue that architects and housebuilders are unable to ignore.

Sadly, the regulations are responding too slowly for some because the current Part O is restricted in scope to new residential buildings, so does not address the existing building stock. The challenge this poses is clear. Only recently the Climate Change Committee published a report outlining how it believes £1billion investment a year is needed to introduce the cooling measures our built environment needs to adapt to our warmer reality. According to the Committee, without action, 92% of homes are likely to suffer from overheating by 2050.

The role of glass in preventing overheating

Much of the discussion on this topic focusses on the pros and cons of active cooling measures like air conditioning. But this leaves one part of the building fabric in every home overlooked – the glass. Alongside passive measures, such as external shading and cross-ventilation, high-performance solar-control glass can make a significant contribution to keeping our interiors cool in the summer.

How our windows are designed has a direct, measurable impact on how warm a room gets on a hot day – the glazing industry today can provide solutions that ensure temperature control in our homes, workplaces and schools.

Finding the right balance between glass that optimises light transmittance while not taking in too much heat has always been an important aspect of building design, but it is increasingly being pushed to the forefront of considerations. Solar-control glass allows daylight to pass through, keeping natural light in our homes, but reflects a significant amount of the sun’s heat back outside.

Take a typical south-facing room in a home that uses double glazing. On a hot summer afternoon its solar gain can quickly push up internal temperatures to unacceptably high levels. But using solar-control glass can reduce those gains and mean people don’t have to close blinds – or switch on air conditioning to cool down.

The importance of being passive

Active cooling measures like air conditioning and heat pumps with built-in cooling capability, which the Climate Change Committee’s report highlights, do have an important role to play. But they need to be paired with passive cooling methods like solar-control glass, which, once installed, are able to work quietly in the background for the lifetime of a building.

Solar-control glass can’t suffer mechanical faults and doesn’t require energy, therefore doesn’t contribute to operation energy requirements. It can help keep buildings at a comfortable temperature without compromising on natural light: a typical product might transmit 70% of daylight while delivering a low g value of 37%.

As a reminder, the g-value (or solar factor) measures how much of the sun’s energy passing through a window ends up as heat inside a building. It is expressed as a number between 0 and 1 (or as a percentage), combining the solar radiation that passes straight through the glass with the share of energy absorbed by the glass and re-radiated inward as heat. The lower the g-value, the less solar heat gain.

Solar-control glazing can be particularly suited to glazing on east, south or west elevations, which are most exposed to the sun in the UK. Good quality solar-control glass should also have a low enough U-value to be good a keeping heat in in the colder months.

The Future Homes Standard, due to come into effect next year, will require new homes in England to align with the UK’s net-zero targets. Energy efficiency is central to this, and the fabric requirements focus mainly on U-values. But better-insulated, more airtight homes are also more prone to overheating – which is where Part O comes in, requiring an overheating risk assessment for new homes. Solar-control glass can help meet that requirement while breaking a feedback loop that’s easy to fall into: hotter summers driving up air-con use, which in turn increases energy consumption and emissions.

Part O reinforces this by requiring that mechanical cooling only be used where insufficient heat can be removed from a building without it. Glass is also a particularly effective passive cooling method, because it works without the occupier having to do anything. Blinds and curtains only work if someone remembers to draw them – solar-control glass works year-round, whether the home is occupied or not.

Bringing glass into the conversation early

For architects, developers and housebuilders, glazing decisions need to be taken early and treated with the same consideration as wall construction or heating systems. Orientation, opening size, shading and glass specification need to be considered together, and specifiers need to be working with manufacturers from the outset.

This is important for new housing, but there is also huge potential for improvement in the retrofitting of our current housing stock. Most homes in the UK weren’t designed with the summers that we are now experiencing in mind. Replacing ineffective or underperforming glazing units with new solar-control glass is an intervention that can be delivered at scale and without major disruption to occupants. It is an accessible upgrade that can help keep our current homes cooler and bring them up to speed with recent regulations for new buildings.

The UK’s overheating problem is not going anywhere and our weather this summer has only served to highlight the importance of addressing the challenges it poses for our built environment. It is set to be one of the defining issues for housebuilding in the modern world – and solar-control glass needs to be treated as part of the toolkit that we use to manage the issue.