Light & Heat

Building regulations throughout the UK and Ireland require building elements, including glazing, to provide thermal insulation. Some buildings may also require solar control, to reduce the potential for overheating, and consequently improved comfort and reduce energy costs for air conditioning.

In order to provide these performance characteristics, insulating glass units (IGU), also often referred to by their construction as double or triple glazing, are commonly used for the majority of glazing solutions. An IGU provides thermal insulation through the use of coated glasses and an inert gas, such as Argon, within the cavity. Coated glasses within an IGU can also provide effective solar control to reduce overheating.

IGUs are manufactured in accordance with EN 1279-5 [1], and associated parts of the EN 1279 series of standards, and comprise two or more panes of glass, a spacer bar and primary and secondary sealants, as illustrated below.

Thermal Insulation

A key factor in insulating glass performance is the presence of a low emissivity coating, such as SGG PLANITHERM TOTAL+, SGG PLANITHERM ONE T or products from the SGG COOL-LITE range, amongst others.

Also of importance is the conductance of the gas within a cavity, and the cavity width. Within the UK, for high performance units, Argon is typically selected, with optimum thermal performance with a 16 mm cavity width.

Combining a low emissivity coating with an Argon filled cavity will provide centre pane U values of as low as 1.0 W/m2K, which when combined with a suitable framing system, will typically exceed the requirements of Building Regulations.


Centre Pane U Value (W/m2K)









Solar Control

As well as offering high thermal efficiency for heat loss, Saint-Gobain Building Glass can also offer products to reduce heat gain, without losing excessive levels of natural daylight. These high selectivity coatings, SGG COOL-LITE SKN and SGG COOL-LITE XTREME, are available over a wide performance range, as below;

Product details are available through the product pages, or the Commercial Brochure.

Measuring Performance

The centre pane performance of glazing is carried out in accordance with EN 410:2011 [2], for light, solar gain and other photometric properties, and EN 673:2011 [2] for U value.

Referenced Documents


European Committee for Standardization, EN 1279-5:2005+A2:2010 - Glass in building. Insulating glass units. Evaluation of conformity, CEN, 2005/2010.


European Committee for Standardization, EN 410:2011 - Glass in building. Determination of luminous and solar characteristics of glazing, CEN, 2011.


European Committee for Standardization, EN 673:2011 - Glass in building. Determination of thermal transmittance (U value). Calculation method, CEN, 2011.