Controlling Solar Gain & Overheating in Highly Glazed Spaces

Solar Gain, also referred to as solar heat gain or passive solar gain, is a term that refers to the increase in temperature in a space or building as a result of solar radiation. There are many ways to control and manage solar gain for effective results. Keep reading to discover the technical solutions on offer at IQ Glass, as well as some external shading solutions to eliminate the risk of overheating in highly glazed spaces.

Solar Gain

The sun's light can be broken down into 3 main parts; ultra-violet rays, infra-red radiation and visible light. It is the ‘infra-red’ element of the sun’s light that causes overheating in highly glazed areas. The sun's radiation travels in short wavelengths through the glazing, the objects inside the living space absorb these short wavelengths of radiation and emit heat at longer infrared wavelengths.

These waves cannot travel through glazing and will be contained within the living space, increasing the internal temperature. This causes the infra-red radiation to be trapped within the space and can cause overheating, referred to as Solar Gain.

South West London glass box extension on top floor

Controlling Solar Gain

Controlling solar gain in a highly glazed environment is possible with the use of Solar Control coatings. These coatings reduce the amount of solar radiation that can enter a space through the glazing and thus reduces the amount of solar gain.

One technical glass solution that IQ offer to combat solar gain is Electro-Chromic Glass, designed to change from clear to dark automatically depending on ambient sunshine, season or atmosphere. This technical glass grants the ability to change the glass G Factor from 0.47 all the way down to a minimum of 0.04, which means that only 4% of the solar infra-red radiation hitting the external face of glass will transmit into the internal spaces.

Using a tinted glass will mean that more of the sun’s rays will be reflected than emitted but this will also alter the natural light transmission. A modern glazing technology using a transparent coating, such as a solar control coating, will reduce the G Factor of the glazing, therefore reducing the amount of infra-red radiation entering a space, with only a small reduction in the visible light transmission.

Managed Solar Gain can actually be used to help supplement your heating system and save money on heating bills by raising temperatures in a room during colder periods. For example, keeping curtains and blinds open on a sunny winter's day will keep a space warm using the solar gain from the sun's radiation, reducing the amount of domestic heating required.

Solar Control Coating applied to glass extension

G-Factor

The G Factor is, also known as the solar factor, is represented as a percentage of the total incident radiation that enters through the glass. This includes the direct radiant influx as well as the infra-red radiation that is absorbed by the glass and then re-emitted internally.

For example, a 53% total radiant influx will be a G Factor of 0.53. The G Factor is measured using a standard testing method EN 410 under the assumption of standard daylight light settings with the internal and external temperatures equal. There are many elements that can alter the G Factor of a glass installation if required.

IQ_Glass_Rusty_House_Solar glass wall

External Shading Solutions

Alternatively, you could shade large elevations of glazing from solar radiation using either internal or external shading solutions. Concealed blind systems would work as an internal solution, blocking the sun when closed whilst maintaining a minimal aesthetic when open. On the external face of a property, large elevations of glass can be shaded by shutter systems or a Louvre roof system.

The Louvre roof system from IQ is designed with flexibility in mind. To reduce solar gain, the aluminium louvres are fully adjustable and can be turned throughout the day to offer the most effective shading angle.

For more information about combatting the effects of solar gain, or to speak to a technical expert about your project, email [email protected].

Umbris- Kingsland Road 02

FAQs

What is solar gain in glazing systems?

Solar gain in glazing systems is the increase in internal temperature caused by solar radiation passing through the glass. In highly glazed spaces, sunlight enters through the glazing and is absorbed by internal surfaces such as floors, walls, furniture and finishes. These surfaces then re-emit the energy as heat, which can become trapped inside the building and raise the temperature of the space.

Solar gain is not always a problem. In colder months, controlled solar gain can help naturally warm a room and reduce reliance on mechanical heating. The issue comes when the level of solar gain is not managed, particularly in highly glazed spaces with large elevations of glass.

This is most relevant to south-facing and west-facing glazing, large sliding glass doors, glass box extensions, structural glass walls, roof glazing and open-plan living spaces with prolonged sun exposure. Coastal homes and exposed sites can also be more affected because the glazed elevations may receive high levels of direct sunlight throughout the day.

The amount of solar gain passing through the glass is measured using the G Factor, also known as the solar factor. A lower G Factor means less solar energy is transmitted through the glazing. By selecting the right glass specification, solar control coating, opening elements and shading strategy, it is possible to maintain the benefits of large architectural glazing while reducing the risk of overheating.

Will a solar control coating change the transparency or appearance of my glass?

A modern solar control coating can reduce solar gain while maintaining a clear, highly transparent appearance. The coating is designed to reduce the amount of solar energy passing through the glass, while still allowing natural light and views to remain central to the design.

Solar control coatings are typically formed from thin metal oxide layers applied within the insulated glass unit. These coatings are available in a range of performance levels, allowing the specification to be balanced around solar control, visible light transmission, external reflection and the desired appearance of the glass.

For many residential and architectural glazing projects, a neutral solar control coating is used because it offers a subtle appearance close to clear glass. For example, a 70/35 solar control coating maintains high light transmission while reducing the G Factor of the glass, helping to control overheating without creating an obviously tinted or heavily reflective elevation.

There can still be a subtle difference in tone, reflection or external appearance depending on the level of solar control required. As a general rule, stronger solar control performance can increase visible reflection or introduce a more noticeable tint. This is why the coating should be selected carefully, particularly on luxury residential projects where transparency, views and the external appearance of the glazing are important.

IQ Glass can advise on the most suitable glass specification for the project, taking into account orientation, glass size, exposure, internal comfort requirements and the architectural design intent. Solar control glass samples and full size glazing examples can also be viewed at the IQ Glass showroom at Sky House.

How expensive is solar control coating?

The cost of solar control coating depends on the glass specification, coating type, glass sizes, system choice and overall project requirements. It should be priced as part of the full glazing specification rather than treated as a standard fixed cost, because the right coating will vary from project to project.

For large areas of south-facing or west-facing glazing, exposed coastal homes, open-plan living spaces and highly glazed extensions, solar control coating is often a valuable specification upgrade. It helps reduce the risk of overheating while preserving the design benefits of large glass elevations, such as natural light, clear views and a minimal architectural appearance.

It is usually more cost effective to consider solar control at the early design or quotation stage than to try to resolve overheating after the glazing has been installed. Retrofitting shading, increasing cooling systems or changing the way a space is used can be more disruptive than specifying the right glass performance from the outset.

Solar control coating should also be considered alongside the wider environmental strategy for the building. In some projects, solar control glass may be enough to manage the risk of overheating. In others, it may need to work with opening glazing, external shading, ventilation, roof overhangs, louvres or automated shading systems.

IQ Glass can provide project specific advice once the glazing sizes, orientation, location and performance requirements are known. This allows the team to recommend a coating that balances comfort, cost, transparency and the architectural intent of the design.

What is solar gain?

Solar gain is the increase in temperature inside a building caused by solar radiation passing through glazing. Infrared radiation enters through the glass in short wavelengths, is absorbed by surfaces inside the space and re-emitted as longer wavelength heat. These longer waves cannot pass back through the glass, so heat builds up inside. Solar gain is also referred to as solar heat gain or passive solar gain. IQ covers the full range of solar control options for structural glass.

Why do glass extensions overheat?

Glass extensions overheat when a large glazed area allows solar radiation to build up without adequate measures to control or remove the heat. The more glazing present, particularly south-facing glass or roof glazing, the greater the risk. Without solar control glass, external shading or sufficient ventilation, internal temperatures in a glass extension can rise quickly during warm weather. IQ recommends solar control glass for all roof glazing, structural glass facades and south-facing glazing.

How do you control solar gain in a highly glazed space?

Solar gain in a highly glazed space can be controlled through a combination of glass specification, shading and ventilation:

Solar control glass with a low g-value to reduce the proportion of solar radiation entering the space.
External shading devices such as louvres or blinds.
Opening glazing elements such as windows or rooflights to allow excess heat to escape.
Electrochromic glass, which switches from clear to tinted on demand to reduce solar radiation.

For a full overview of available options, see IQ's guide to solar control options for structural glass.

What is solar control glass?

Solar control glass is glass with a metal oxide coating on the internal face of the outer pane that reflects solar radiation away from the glazing. The effectiveness is measured by the g-value, which represents the proportion of solar energy that passes through the unit. IQ's most popular 70/35 solar control coating maintains light transmission at 70% while reducing the g-value to 35%, meaning only 35% of solar radiation enters the space. View the full range of solar control glass options from IQ.

Does triple glazing reduce solar gain?

Triple-glazing has a lower g-value than double-glazing, meaning less solar radiation passes through the unit, making it more effective at reducing solar gain. A standard double-glazed unit with low-e coating has a g-value of around 0.64, while a triple-glazed equivalent can achieve a g-value of around 0.53. Triple glazing also offers improved thermal performance and air permeability, making it a strong choice for highly glazed spaces where overheating is a concern. IQ's guide to double glazed Vs triple glazed sliding doors covers the performance differences in detail.