FAQ’s

It allows better thermal insulation to be achieved without the need to change the window framing system of an existing house as this would normally have to be undertaken if double glazed units were specified because they are often too thick to fit in normal framing.

It’s the Low E coating on the inside of the building that will reduce heat loss in winter and re-radiation to the inside in summer. This allows a very cost effective balance of performance to be achieved in a relatively thin glass.

When it’s a laminate, it achieves a Grade A safety rating and can be used in low level glazing and in other areas where safety glass is required.

There are a range of options available dependent on whether a single glazed (monolithic) or double glazed solution is required. That in turn may depend on the framing system desired, the performance criteria required and/or the budget that is in place.

Essentially the performance criteria revolve around blending the solar control and thermal insulation properties of the glass to reduce the amount of heat coming through the glass in Summer and reducing the amount of heat lost to the outside in Winter.

Single glazed options available from Viridian include ComfortPlus™ SmartGlass™ EVantage™ EnergyTech™ & SolTech™

Each product offers different options which can match the customer requirements in terms of solar control, light transmission, reflectivity, thermal efficiency, safety and colour.

Double glazed options permit a wider range of products to be considered across the range and generates the potential for higher performance levels to be achieved; i.e. lower U values in conjunction with greater levels of solar control and higher levels of light transmission.

Low E means ‘low emissivity.’ The main difference between a Low E glass and an ordinary glass is that Low E glass has a very thin coating applied to one side of the glass. This enables the transport of heat through the glass to be reduced. EnergyTech™ and ComfortPlus™ are all examples of a Low E glass. The main benefits of using such a glass are that more warmth is kept within the room, more space can be used within the room as cold downdraughts are minimised, more window area can be used, heating costs are reduced and the contribution the products make in reducing greenhouse emissions.

The Low E coating is actually harder than the glass and consequently is quite difficult to scratch. This does not mean it cannot be scratched, as anything can be scratched if you try hard enough. However, the marks you notice might be abrasion marks. The consequence of the coating being very hard is that it can abrade other materials? So, materials rubbed across the coating can abrade and leave deposits on the surface. For example, if you rub a coin across the coating, a mark will result. The mark is caused by metal from the coin being deposited on the coating. These abrasion marks can be cleaned off and advice on how to do this can be found in the cleaning advice for Low E glass which can be found on our website.

U value is the measure of the insulating capacity of the glass. This represents how quickly heat from hot air (not direct sunlight) will pass through the glass. The lower the U value the better the insulation. Glass with low U values are generally used to keep the warmth in the room, in cold climates or at night.

For example, 4mm clear float glass has a U value of 5.9, whilst ComfortPlus™ has a U value of 3.6. So ComfortPlus™ is a better insulating product than 3mm clear float glass.

Solar Heat Gain Co-efficient (SHGC) is the amount of heat from direct sunlight that passes through the glass. This includes sunlight which passes directly through the glass to the room and the amount of sunlight which is absorbed by the glass and later reradiated to the room. The lower the SHGC, the better it will achieve this. Glass with a low SHGC is best used in areas of direct sunlight, for example to reduce the amount of heat coming through the windows in summer.

For example, our 4mm clear float glass has an SHGC of 0.85, whilst ComfortPlus™ has an SHGC between 0.57 and 0.60 depending on the colour. 

It reduces some of the direct heat from the sun passing to the inside of the building. The amount will depend on both the colour of the glass and its thickness. Toned glass is available in a range of colours to enable different aesthetics and performance of the building to be achieved.

Toned glass can be easily incorporated into a double glazed unit if required and can assist in reducing glare, it can be laminated or toughened if required.

Toned glass provides a degree of privacy (depending on colour). However unless incorporated with a Low E coating or used in a double glazed unit it remains poor in its insulation benefits. Clear glass and SuperGrey™ glass have the same insulative benefits, which are the worst in terms of insulation performance

R value is a measure of how well a material resists heat transfer whereas U value is a measure of how well a material transmits heat. As such, solid materials such as bricks, insulation and walls are measured in R-values whilst glass is measured in U values. Unlike glass where lower U values mean better insulation, for materials that are measured in R values it is the higher the R value the better the insulation. Conversion between the two can be achieved using the following relationship U value =1/R.

It is a difference between both the type of material used for the coating and the way the coating is applied to the glass.

However, there are several further differences:

Soft coated Low E glasses must be incorporated into a double glazed unit as the coating is ‘less durable’ than a hard coated (pyrolytic) coating when exposed to the atmosphere. Soft coated Low E glasses cannot be glazed in single glazed applications but hard coated products such as ComfortPlus™ and EnergyTech™ can.

Pyrolytic coatings have a long shelf life, whereas soft coated Low E glasses do have a shelf life and will begin to break down if stored for too long without being incorporated into double glazed units.

Soft coat Low E glasses such as Viridian LightBridge™ or PerformaTech™ have significantly lower U values than hard coated pyrolytic glass types.

Hard-coated Low E glasses are manufactured online during the float manufacturing process where soft coats are applied by a special offline process at some time after the glass has been manufactured.

If condensation forms on the coated surface of a single glazed Low E glass, e.g. ComfortPlus™,  the glass loses its low emissivity performance characteristics and behaves like normal float glass. In other words, it provides no additional benefits in terms of reducing heat loss from the building whilst the condensation is present. If there is a chance of condensation forming on the inside of the window on the coated glass surface (i.e. in very cold climates), then the best solution is to use a double glazed unit incorporating a low emissivity glass. This further reduces the U value of the glass, keeps the inner face of the double glazed unit warmer and therefore minimises the chances of condensation forming.

The fact that there is a Low E coating on one surface of the glass, glazed to the inside, means that the glass will have a lower U value and hence provide better levels of insulation than normal clear glass. This is because the coating reflects the heat back into the room whereas glass without a Low E coating would allow the heat from the room to pass through it. A good example of this is 6.38mm ComfortPlus™ which has a U value of 3.6 compared to a 6mm clear float glass which has a U value of 5.8, an improvement of over 39%.

A low emissivity glass can specifically enhance the thermal insulation of double glazed units. It achieves this by being positioned in the insulating unit with the coating on the glass surface facing the cavity.

In a double glazed unit, counting the surfaces from the exterior of the building, the coating should be on surface 2 (the inner surface of the outer pane) or surface 3 (the cavity surface of the inner pane).

Low E coatings perform the function of enhancing the thermal insulation (reducing the U value) equally well whether it is positioned on surface 2 or surface 3.

General advice is that the preferred location of the coating is on surface 2 of the unit, but if the glass types used in the unit make it difficult to assemble the unit than surface 3 can be selected.

There is no loss of insulation performance by using it on surface 3 however SHGC performances will vary.

When Viridian LightBridge™ is used the coating is installed on surface 3 of the double glazing unit.

The U value for a window is the combination of the U value of the glass and the U value of the frame. The frame is made of a different material to the glass so will have a different U value to the glass. The overall U values of window system using aluminium, timber or PVC frames for example will all be different even if the same glass is used in each case. Because aluminium frames have a higher U value than those of either timber or PVC, the overall U value of an aluminium system is higher and as such is less effective as a thermal insulator.

ComfortPlus™ Clear can be used where passive solar design principles are used because it has a higher solar heat gain coefficient (SHGC) than ComfortPlus™ Neutral. Consequently, it has a higher solar heat gain, so it allows more energy through, making it suitable for north facing buildings during the winter months where it can gain from free heat (energy). ComfortPlus Clear has the same colour reflectance as ordinary clear glass where Neutral has a blueish grey appearance.

Its main function is to reduce the level of solar radiation entering a building. Toned glasses achieve this by absorbing a percentage of the solar radiation within the body of the glass itself whilst coated glasses achieve this by both reflecting and absorbing the solar radiation.

A very cost effective way of reducing glare is by the use of toned glass. The inherent nature of toned glass means that glare is reduced due to the toning through the body of the glass. The amount of light transmittance is reduced to different degrees dependent on the colour of toned glass as will be the amount of glare.

For example,

VFloat™ Grey will reduce glare more effectively than Viridian VFloat™ Green because its level of light transmittance is lower.

SuperTones product, VFloat SuperGrey™, is very effective at minimising glare with only 9% light transmittance.

Coated glasses, for example EVantage™, offer much higher levels of solar and glare control due to the application of specialty coatings especially when applied to toned glass.

Thermal breakage refers to the cracking of annealed glass cracking due to the build-up of excessive thermal stress developed because of a differential in temperature across the glass. As there is more risk associated with glasses which absorb more solar heat within the body of the glass, there is increased risk of a solar control glass being more susceptible to thermal fracture. We would always recommend that a thermal safety check be undertaken when a solar control glass is being specified to determine whether the glazing is at risk from thermal fracture. An effective way to eliminate breakage by thermal fracture is to heat strengthen or toughen the glass.

The different colours across the solar control range absorb solar heat to different degrees and is mainly a function of the amount of colourant that is present within the glass mix when each of the products is manufactured. The role of a solar control glass is to control the amount of solar infrared (heat) transmitted through the glass. Whilst this is controlled via reflectance as well as absorption, the amount of heat absorbed by the glass will be determined by the amount and properties of the colourant within the glass.

Colour density increases with glass thickness, so the colour of toned glass becomes more intense as the thickness increases. As a consequence, the use of the same thickness of toned glass is required to keep the colour of a building the same. The use of a toned laminated glass will delivery colour consistency across various glass thicknesses.

Solar control glasses do reduce Ultra Violet (UV) rays from the sun to different degrees. However, apart from Viridian VFloat SuperGrey™ which reduces UV transmission by 99%, the best way to eliminate UV transfer through the glazing is to incorporate a laminated glass in the glazing. All laminated glass eliminates more than 99% of UV, even in its clear form.

The key differences are that Viridian SuperToned glasses provide significant improvements in solar control performance whilst providing excellent daylight transmission performance. Viridian VFloat SuperGrey™ provides exceptional solar control properties (with a SHGC of .35) without the need for a solar control coating however one drawback is its low light transmittance of 8%.

The coating is actually very difficult to scratch and is harder than the glass. For example, if you scratch the coating with a coin, it is the metal from the coin you see deposited on the glass surface itself rather than a scratch. For that reason, it is advised that metal objects are kept away from the glass surface as much as possible and certainly no metal objects, especially sharp metal objects such as razor blades, should be used to clean ‘stubborn marks’ on the glass. Instructions on the cleaning can be found here. 

Filling with Argon gas instead of air will improve the insulating capacity of the double glazed unit. This is reflected by a lower U value than would result from the use of air. The magnitude of the benefit varies with the size of the gap between the glasses in the IGU. The use of Argon in a 12mm gap will result in an improvement of approximately 6%. Viridian only supply Argon gas as a standard across our complete double glazed range.

It allows better thermal insulation to be achieved without the need to change the window framing system of an existing house as this would normally have to be undertaken if double glazed units were specified because they are often too thick to fit in normal framing.

It’s the Low E coating on the inside of the building that will reduce heat loss in winter and re-radiation to the inside in summer. This allows a very cost effective balance of performance to be achieved in a relatively thin glass.

When it’s a laminate, it achieves a Grade A safety rating and can be used in low level glazing and in other areas where safety glass is required.

There are a range of options available dependent on whether a single glazed (monolithic) or double glazed solution is required. That in turn may depend on the framing system desired, the performance criteria required and/or the budget that is in place.

Essentially the performance criteria revolve around blending the solar control and thermal insulation properties of the glass to reduce the amount of heat coming through the glass in Summer and reducing the amount of heat lost to the outside in Winter.

Single glazed options available from Viridian include ComfortPlus™ SmartGlass™ EVantage™ EnergyTech™ & SolTech™

Each product offers different options which can match the customer requirements in terms of solar control, light transmission, reflectivity, thermal efficiency, safety and colour.

Double glazed options permit a wider range of products to be considered across the range and generates the potential for higher performance levels to be achieved; i.e. lower U values in conjunction with greater levels of solar control and higher levels of light transmission.

Low E means ‘low emissivity.’ The main difference between a Low E glass and an ordinary glass is that Low E glass has a very thin coating applied to one side of the glass. This enables the transport of heat through the glass to be reduced. EnergyTech™ and ComfortPlus™ are all examples of a Low E glass. The main benefits of using such a glass are that more warmth is kept within the room, more space can be used within the room as cold downdraughts are minimised, more window area can be used, heating costs are reduced and the contribution the products make in reducing greenhouse emissions.

The Low E coating is actually harder than the glass and consequently is quite difficult to scratch. This does not mean it cannot be scratched, as anything can be scratched if you try hard enough. However, the marks you notice might be abrasion marks. The consequence of the coating being very hard is that it can abrade other materials? So, materials rubbed across the coating can abrade and leave deposits on the surface. For example, if you rub a coin across the coating, a mark will result. The mark is caused by metal from the coin being deposited on the coating. These abrasion marks can be cleaned off and advice on how to do this can be found in the cleaning advice for Low E glass which can be found on our website.

U value is the measure of the insulating capacity of the glass. This represents how quickly heat from hot air (not direct sunlight) will pass through the glass. The lower the U value the better the insulation. Glass with low U values are generally used to keep the warmth in the room, in cold climates or at night.

For example, 4mm clear float glass has a U value of 5.9, whilst ComfortPlus™ has a U value of 3.6. So ComfortPlus™ is a better insulating product than 3mm clear float glass.

Solar Heat Gain Co-efficient (SHGC) is the amount of heat from direct sunlight that passes through the glass. This includes sunlight which passes directly through the glass to the room and the amount of sunlight which is absorbed by the glass and later reradiated to the room. The lower the SHGC, the better it will achieve this. Glass with a low SHGC is best used in areas of direct sunlight, for example to reduce the amount of heat coming through the windows in summer.

For example, our 4mm clear float glass has an SHGC of 0.85, whilst ComfortPlus™ has an SHGC between 0.57 and 0.60 depending on the colour. 

It reduces some of the direct heat from the sun passing to the inside of the building. The amount will depend on both the colour of the glass and its thickness. Toned glass is available in a range of colours to enable different aesthetics and performance of the building to be achieved.

Toned glass can be easily incorporated into a double glazed unit if required and can assist in reducing glare, it can be laminated or toughened if required.

Toned glass provides a degree of privacy (depending on colour). However unless incorporated with a Low E coating or used in a double glazed unit it remains poor in its insulation benefits. Clear glass and SuperGrey™ glass have the same insulative benefits, which are the worst in terms of insulation performance

R value is a measure of how well a material resists heat transfer whereas U value is a measure of how well a material transmits heat. As such, solid materials such as bricks, insulation and walls are measured in R-values whilst glass is measured in U values. Unlike glass where lower U values mean better insulation, for materials that are measured in R values it is the higher the R value the better the insulation. Conversion between the two can be achieved using the following relationship U value =1/R.

It is a difference between both the type of material used for the coating and the way the coating is applied to the glass.

However, there are several further differences:

Soft coated Low E glasses must be incorporated into a double glazed unit as the coating is ‘less durable’ than a hard coated (pyrolytic) coating when exposed to the atmosphere. Soft coated Low E glasses cannot be glazed in single glazed applications but hard coated products such as ComfortPlus™ and EnergyTech™ can.

Pyrolytic coatings have a long shelf life, whereas soft coated Low E glasses do have a shelf life and will begin to break down if stored for too long without being incorporated into double glazed units.

Soft coat Low E glasses such as Viridian LightBridge™ or PerformaTech™ have significantly lower U values than hard coated pyrolytic glass types.

Hard-coated Low E glasses are manufactured online during the float manufacturing process where soft coats are applied by a special offline process at some time after the glass has been manufactured.

If condensation forms on the coated surface of a single glazed Low E glass, e.g. ComfortPlus™,  the glass loses its low emissivity performance characteristics and behaves like normal float glass. In other words, it provides no additional benefits in terms of reducing heat loss from the building whilst the condensation is present. If there is a chance of condensation forming on the inside of the window on the coated glass surface (i.e. in very cold climates), then the best solution is to use a double glazed unit incorporating a low emissivity glass. This further reduces the U value of the glass, keeps the inner face of the double glazed unit warmer and therefore minimises the chances of condensation forming.

The fact that there is a Low E coating on one surface of the glass, glazed to the inside, means that the glass will have a lower U value and hence provide better levels of insulation than normal clear glass. This is because the coating reflects the heat back into the room whereas glass without a Low E coating would allow the heat from the room to pass through it. A good example of this is 6.38mm ComfortPlus™ which has a U value of 3.6 compared to a 6mm clear float glass which has a U value of 5.8, an improvement of over 39%.

A low emissivity glass can specifically enhance the thermal insulation of double glazed units. It achieves this by being positioned in the insulating unit with the coating on the glass surface facing the cavity.

In a double glazed unit, counting the surfaces from the exterior of the building, the coating should be on surface 2 (the inner surface of the outer pane) or surface 3 (the cavity surface of the inner pane).

Low E coatings perform the function of enhancing the thermal insulation (reducing the U value) equally well whether it is positioned on surface 2 or surface 3.

General advice is that the preferred location of the coating is on surface 2 of the unit, but if the glass types used in the unit make it difficult to assemble the unit than surface 3 can be selected.

There is no loss of insulation performance by using it on surface 3 however SHGC performances will vary.

When Viridian LightBridge™ is used the coating is installed on surface 3 of the double glazing unit.

The U value for a window is the combination of the U value of the glass and the U value of the frame. The frame is made of a different material to the glass so will have a different U value to the glass. The overall U values of window system using aluminium, timber or PVC frames for example will all be different even if the same glass is used in each case. Because aluminium frames have a higher U value than those of either timber or PVC, the overall U value of an aluminium system is higher and as such is less effective as a thermal insulator.

ComfortPlus™ Clear can be used where passive solar design principles are used because it has a higher solar heat gain coefficient (SHGC) than ComfortPlus™ Neutral. Consequently, it has a higher solar heat gain, so it allows more energy through, making it suitable for north facing buildings during the winter months where it can gain from free heat (energy). ComfortPlus Clear has the same colour reflectance as ordinary clear glass where Neutral has a blueish grey appearance.

Its main function is to reduce the level of solar radiation entering a building. Toned glasses achieve this by absorbing a percentage of the solar radiation within the body of the glass itself whilst coated glasses achieve this by both reflecting and absorbing the solar radiation.

A very cost effective way of reducing glare is by the use of toned glass. The inherent nature of toned glass means that glare is reduced due to the toning through the body of the glass. The amount of light transmittance is reduced to different degrees dependent on the colour of toned glass as will be the amount of glare.

For example,

VFloat™ Grey will reduce glare more effectively than Viridian VFloat™ Green because its level of light transmittance is lower.

SuperTones product, VFloat SuperGrey™, is very effective at minimising glare with only 9% light transmittance.

Coated glasses, for example EVantage™, offer much higher levels of solar and glare control due to the application of specialty coatings especially when applied to toned glass.

Thermal breakage refers to the cracking of annealed glass cracking due to the build-up of excessive thermal stress developed because of a differential in temperature across the glass. As there is more risk associated with glasses which absorb more solar heat within the body of the glass, there is increased risk of a solar control glass being more susceptible to thermal fracture. We would always recommend that a thermal safety check be undertaken when a solar control glass is being specified to determine whether the glazing is at risk from thermal fracture. An effective way to eliminate breakage by thermal fracture is to heat strengthen or toughen the glass.

The different colours across the solar control range absorb solar heat to different degrees and is mainly a function of the amount of colourant that is present within the glass mix when each of the products is manufactured. The role of a solar control glass is to control the amount of solar infrared (heat) transmitted through the glass. Whilst this is controlled via reflectance as well as absorption, the amount of heat absorbed by the glass will be determined by the amount and properties of the colourant within the glass.

Colour density increases with glass thickness, so the colour of toned glass becomes more intense as the thickness increases. As a consequence, the use of the same thickness of toned glass is required to keep the colour of a building the same. The use of a toned laminated glass will delivery colour consistency across various glass thicknesses.

Solar control glasses do reduce Ultra Violet (UV) rays from the sun to different degrees. However, apart from Viridian VFloat SuperGrey™ which reduces UV transmission by 99%, the best way to eliminate UV transfer through the glazing is to incorporate a laminated glass in the glazing. All laminated glass eliminates more than 99% of UV, even in its clear form.

The key differences are that Viridian SuperToned glasses provide significant improvements in solar control performance whilst providing excellent daylight transmission performance. Viridian VFloat SuperGrey™ provides exceptional solar control properties (with a SHGC of .35) without the need for a solar control coating however one drawback is its low light transmittance of 8%.

The coating is actually very difficult to scratch and is harder than the glass. For example, if you scratch the coating with a coin, it is the metal from the coin you see deposited on the glass surface itself rather than a scratch. For that reason, it is advised that metal objects are kept away from the glass surface as much as possible and certainly no metal objects, especially sharp metal objects such as razor blades, should be used to clean ‘stubborn marks’ on the glass. Instructions on the cleaning can be found here. 

Filling with Argon gas instead of air will improve the insulating capacity of the double glazed unit. This is reflected by a lower U value than would result from the use of air. The magnitude of the benefit varies with the size of the gap between the glasses in the IGU. The use of Argon in a 12mm gap will result in an improvement of approximately 6%. Viridian only supply Argon gas as a standard across our complete double glazed range.