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05 May 2021

Solar Control Glass: Get the Best of Both Worlds

With the right glass, there is no longer a trade-off between large expanses of glazing and excessive heating, as Phil Brown, European Regulatory Marketing Manager at Pilkington United Kingdom – part of the NSG Group – explains.

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More and more, so it seems to me, light is the beautifier of the building,” so said Architect Frank Lloyd Wright. For those who design homes, whether they are world-famous architects, self-builders or renovators, optimising the daylight inside the building is typically a key objective.

In our recent study of 2000 homeowners, we found that natural light was the most sought-after attributes of a dream home. It was considered more important than features including large gardens, private driveways and a countryside location. For these reasons, sunlight can have a fundamental bearing on project decisions.

You might look to position the busiest parts of your home – like the kitchen and living spaces – where they will benefit from the southern aspects that provide the most natural light. Coupled with this, you may want to maximise the glazing in the building’s envelope to brighten spaces. However, this is where you will need to tread carefully, as large areas of glazing will always carry the risk of excessive heat build-up – unless you choose the right glass.

How does solar-control glass help provide year-round comfort?

Specifying large windows – or increasing their size in the case of a renovation – and choosing roof glazing such as skylights, lanterns or entirely glazed roof panels is a great way to brighten your home and make it feel more spacious. But, because all this glazing allows in heat energy from the sun, it often results in spaces quickly overheating on warmer days. Unless houses are very well-ventilated or use air conditioning, this can make rooms less pleasant and comfortable to inhabit, as well as leading to increased energy bills due to the need to implement cooling systems. This is where solar-control glass comes in. Over the years, glass manufacturers have developed advanced coatings that reduce the amount of the sun’s heat transmitted through the glass, whilst maximising daylight admission. The benefit of this is that you can still enjoy spaces that are flooded with glorious natural light without an accompanying overheating effect.

So how does it work?

The coatings that are applied to the glass are engineered to reflect light of a specific range of wavelengths – those that are not visible to the human eye but which do carry a lot of heat energy. By selectively reflecting more of the near-infrared energy but still allowing in a large amount of energy from the visible region, solar control glass significantly reduces internal heating while maintaining clear views and bright spaces. Today, a wide array of different solar control glass products are available, offering a range of different amounts of solar energy and visible light that can pass through them.

One size does not fit all

The maximum temperatures that any given space experiences – and whether it is a problem in your building in terms of overheating – changes case by case, according to a range of factors, so it’s important to choose solar control glass that is right for the specific windows in question.

In hot climates, or where there is extensive glazing in a south-facing aspect that is prone to overheating, it is best to choose glass with a lower g value. A glass with a lower g value will allow less of the sun’s energy to be transmitted compared with one with a higher g value. However, a glass with a lower g value will also generally reduce overall light transmittance, compared with one with a higher g value, thus reducing the amount of daylight that enters the space. Therefore, in more temperate climates – such as in the UK – the best glass to choose will often be one that offers a good balance between solar control and light transmittance.

Solar control glass is typically sold based on a descriptive code, with the first number stating its light transmittance and the second referring to its g value. For example, a glass with a descriptive code of 70/40 typically allows 70% of visible light to pass through, and 40% of total solar heat energy may be a reasonable solution for the vertical glazing of a building in a temperate climate where overheating will only be an issue for limited periods in the year.

On the other hand, a glass with a light transmittance of 30% visible light and a g value of 16% – for example, Pilkington Suncool 30/16 – may be more appropriate in large glazed roofs or for hotter climates where the risk of overheating is a much bigger year-round issue.

Building-integrated photovoltaics (BIPV)

Another long-standing trend for commercial housing developers and self-builders is maximising the energy performance of a building, and solar photovoltaics are increasingly being used to generate power on site to cut bills and increase efficiency. These can open up new possibilities because you no longer need to choose between using a wall or roof space to hold PV panels or adding a window or skylight to allow light into your home. BIPV glazing can do both at once. These products often have visible lines inside the glass where the PV strips sit, and these have a very distinct appearance. They will also naturally reduce the amount of sunlight that is allowed into the building, potentially helping to tackle overheating at the same time.

Ultimately, the wide range of solar control glazing products that are on the market today mean that you, as a home designer or renovator, no longer need to choose between spaces flooded with natural light and comfortable areas in which the climate can be efficiently controlled. With the right solar control glazing, you can truly get the best of both worlds.

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