Technical Advice | Technical Glazing Terms
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Large areas of architectural glazing can transform a building, bringing in natural daylight, creating strong visual connections with the surrounding environment and opening up internal spaces.
However, extensive glazing can also increase solar gains and contribute to overheating, particularly where large glazed areas are exposed to high levels of solar radiation.
Solar control glass is designed to help manage these solar gains. By controlling the amount of solar energy transmitted through the glazing, solar control glass can help reduce heat build-up while maintaining the levels of natural daylight and visual connection required by the design.
Selecting the right solar control glass is not simply a case of choosing the lowest available G-value. The glazing specification needs to consider solar performance alongside visible light transmission, thermal performance, appearance, orientation, glazed area, shading and the intended use of the space.
This guide explains how solar control glass works, the key performance characteristics to consider and how to approach its specification across residential, commercial and architectural glazing projects.
Solar control glass is a type of high-performance glazing designed to manage the amount of solar energy passing through a glazed unit.
When sunlight reaches a pane of glass, the solar radiation can be transmitted through the glass, reflected from its surface or absorbed by the glass and subsequently released as heat. Solar control glass uses specialist coatings or glass compositions to alter this balance and reduce the amount of solar energy transmitted into the building.
This makes solar control glazing particularly relevant to buildings with large areas of glass, including:
Solar control glass can be specified as part of a wider insulating glazing unit and can be combined with other performance requirements, including low U-values, acoustic performance, safety and security requirements.
The correct specification depends on the individual project. Factors such as the building's orientation, the size and location of the glazing, shading, required daylight levels and intended use of the space all influence the most appropriate solution.
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Solar control glass works by controlling how solar radiation interacts with the glazing.
Specialist solar control coatings can selectively reduce the amount of solar energy transmitted through the glass while allowing a significant proportion of visible light to pass through. This allows the glazing to provide solar protection without necessarily requiring heavily tinted or visibly dark glass.
The performance of the glazing is determined by the combination of its solar, thermal and optical characteristics.
When solar radiation reaches the glazing, some energy is transmitted through the glass, some is reflected and some is absorbed.
A solar control coating can alter these proportions, reducing the amount of solar energy entering the building.
This is commonly expressed through the G-value, which is one of the most important performance characteristics when specifying solar control glass.
A lower G-value means that less solar energy is transmitted through the glazing. However, the lowest possible G-value is not automatically the most appropriate choice for every project.
Reducing solar transmission can also affect visible light transmission, appearance and the overall balance of the glazing specification.
Solar control glass can form an important part of an overheating strategy, but glazing should not be considered in isolation.
The amount of solar heat entering a building is also influenced by factors including:
Solar control glazing therefore needs to be considered as part of the wider environmental and building-performance strategy.
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There are several performance characteristics that need to be considered when selecting solar control glass. G-value, visible light transmission, U-value and the appearance of the glazing all contribute to how the glass performs and how it will look once installed.
The G-value, also known as the total solar energy transmittance or solar factor, describes the amount of solar energy that passes through the glazing. In simple terms, a lower G-value means less solar energy is transmitted through the glass.
Reducing solar transmission can also influence visible light transmission and the appearance of the glass. The G-value therefore needs to be considered alongside the wider requirements of the building rather than as a standalone performance figure.
Visible light transmission describes the proportion of visible light that passes through the glazing. For highly glazed buildings, maintaining natural daylight can be just as important as controlling solar gains, particularly where large areas of glass form a key part of the architectural design.
Two glass products can provide similar levels of solar control while offering different levels of visible light transmission. This can affect the amount of daylight entering the space as well as the perceived appearance of the glazing.
When assessing the balance between solar control and daylight, it is therefore important to consider:
U-value describes the rate at which heat is transferred through the glazing due to a temperature difference between the inside and outside of the building. A lower U-value indicates better thermal insulation.
U-value and G-value measure different aspects of glazing performance. Solar control primarily concerns the amount of solar energy entering the building, while U-value relates to heat transfer through the glazing.
These characteristics should be considered together when developing the complete glazing specification.
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Solar control coatings can also influence the visual appearance of the glazing. Depending on the coating and glass make-up, the finished glass may have a neutral appearance or exhibit different levels of external reflection, colour or visual variation.
For large areas of architectural glazing, the appearance of the glass should be considered alongside its technical performance. A small glass sample can also appear different from a large installed façade depending on lighting conditions, surrounding materials, viewing angles and the scale of the installation.
Where appearance and consistency are important, reviewing glass samples during the design and specification process can help establish how the selected coating will look within the wider architectural context.
Ultimately, solar control glass should not be specified around a single performance value. The most appropriate solution is one that provides the required balance between solar control, natural daylight, thermal performance and appearance for the building and its intended use.
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Solar control glass is available in a range of specifications, allowing the glazing to be selected according to the solar, thermal, optical and aesthetic requirements of a project.
Different solar control coatings can provide different combinations of G-value, visible light transmission and appearance. The most appropriate solution therefore depends on what the glazing needs to achieve rather than simply selecting a particular type of glass.
Solar control glass can also be incorporated into double- or triple-glazed units and combined with other performance requirements. The final specification may therefore need to consider:
Solar control glass and Low-E glass perform different functions, although both can form part of a high-performance glazing specification.
Low-E, or low-emissivity, coatings are primarily used to improve the thermal insulation of glazing by reducing radiative heat transfer. Solar control coatings are primarily used to manage solar gains and reduce the amount of solar energy transmitted through the glass.
Modern glazing units can incorporate both characteristics, allowing the glass to provide thermal insulation while also controlling solar gains. The important consideration is therefore the performance of the complete glazing unit rather than treating Low-E and solar control glass as interchangeable specifications.
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Solar control glass can be used across a wide range of architectural applications where large areas of glazing, solar exposure or overheating need to be considered.
Glazed façades and windows can introduce significant levels of solar radiation into a building, particularly where extensive areas of glass are used. Solar control glazing can help manage these gains while maintaining the daylight, views and visual connection that large areas of glazing provide.
Slim sliding glass doors, where extensive glazed areas can form a significant part of the building envelope. Solar control glass can be incorporated into the insulating glass unit to help manage solar gains without compromising the transparency and openness associated with large-format doors.
Solar control glass can also be used in structural glazing, where very large areas of glass can make solar performance particularly important. Structural requirements, glass size, safety and the complete glazing build-up must all be considered alongside solar control.
For more detailed information, see our guide to Solar Control Options for Structural Glass.
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The right solar control glass should be selected as part of the complete glazing specification rather than as an isolated product decision.
The orientation of the glazing is an important starting point. Different elevations can experience different levels and patterns of solar exposure, meaning that the same glass specification may not necessarily be appropriate across an entire building.
The size and proportion of the glazed area should also be considered. As the amount of glazing increases, the potential contribution of solar gains to the internal environment can also increase. This makes early consideration of solar control particularly important on projects with large-format glazing.
The required level of natural daylight is another key consideration. Reducing solar transmission should not automatically mean significantly reducing visible light transmission. The relationship between the two should be considered when selecting the coating and overall glazing build-up.
The appearance of the glass should also form part of the specification. Colour, neutrality, reflectivity and consistency can all influence the finished appearance of a façade, particularly where large areas of glazing are used.
The complete glazing specification may therefore need to consider:
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One common mistake is choosing the lowest available G-value by default. While a lower G-value can provide greater solar control, it may not provide the right balance between solar performance, daylight and appearance for the particular building.
Another is treating every elevation in the same way. Different orientations can experience different solar conditions, so the most appropriate glazing specification may vary across the building.
It is also important not to consider glazing without considering shading. External shading can have a significant influence on solar gains and should be considered alongside the glass rather than as a separate late-stage decision.
Finally, solar control should not be left until the end of the design process. Considering the glazing specification early allows the required solar, thermal, optical and aesthetic performance to be developed alongside the architecture.
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Solar control glass should be specified according to the performance and design requirements of each individual project.
We can help assess your glazing requirements and identify a suitable specification based on factors including glass size, orientation, solar performance, thermal performance, visible light transmission and architectural appearance.
Planning a project requiring high-performance solar control glass? Contact IQ Glass for technical advice on solar control coatings, G-values, daylight, overheating and the specification of glazing for large architectural applications.
What is solar control glass?
Solar control glass is designed to reduce the amount of solar energy entering a building through its glazing. It typically uses a solar control coating or tinted glass to reflect or absorb a proportion of solar radiation while allowing controlled levels of natural daylight to pass through.
It is commonly specified where large areas of glazing could contribute to excessive solar gain and overheating, particularly on south-facing elevations, roof glazing, sliding doors and large architectural glazing.
Does solar control glass reduce overheating?
Yes. Solar control glass can help reduce overheating by limiting the amount of solar energy transmitted through the glazing. Its effectiveness depends on factors including the glass specification, G-value, orientation, size of the glazed area and the internal use of the space.
For example, a south-facing extension with large areas of glazing may require a different solar control specification from a north-facing elevation. Solar control glazing should therefore be selected as part of the wider approach to managing solar gain and overheating.
Is solar control glass the same as Low-E glass?
No. Although both can form part of a high-performance glazing specification, they address different aspects of glazing performance.
Solar control glass is primarily used to reduce solar gain and control the amount of solar energy entering a building. Low-E glass is primarily designed to improve thermal insulation by reducing heat transfer through the glazing.
Modern insulating glass units can incorporate both solar control and low-emissivity properties, allowing the glazing to provide a balance between solar control and thermal performance.
Can solar control glass be used in triple glazing?
Yes. Solar control glass can be incorporated into triple-glazed units where the required performance can be achieved within the overall glass build-up.
The solar control coating, glass positions, cavity configuration and other components of the unit should be considered together to achieve the required combination of solar, thermal and daylight performance.
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