EUROPEAN REFERENCE GLAZING STANDARDS

Technical Terms

The data for performance of windows is for heat losses, solar heat gains and for light transmission. There are three main things to consider, solar gain through the window, light levels from the sun inside the room and heat losses through the window in the heating season.

The properties for the glazing are the solar energy transmittance (the g value), the visible light transmittance (Tvis) and the heat loss co-efficient (U value).

The properties for glazing when combined with shading (referred to as complex glazing systems) are Gtot. Tvis and Utot.

The technical descriptions of the main terms for glazing and shading are described in the boxes.¹

Main European Standards

There are two International standards that were developed separately and have slightly different values. The differences relate to the standards used for the glazing calculations and are an historic issue that is difficult to resolve. In Europe EN ISO 52022 is mostly used and in USA EN ISO 15099 is preferred. The outputs from the ES-SDA database are thus to the ISO EN 52022 standards.

The EN standards were revised in 2017 at which time the reference glazing default values were adjusted to account for improvements in performance of glazing systems when combined with shading devices. That meant that manufacturers needed to adjust their stated performance values. It does not affect single and double clear but there are slight adjustments to the performance of low-e and solar control glazing, this has little effect on external shading but will have slight differences on internal shading.

When comparing product performance from manufacturer’s data sheets check that you have the up-to-date information.

EN ISO 52022

There are two calculation methods for shading performance:

The simplified method EN ISO 52022/1 was developed to enable a manual calculation and was devised at the time when computing power for complex calculations was not easily available. Most data is currently calculated to the simplified method.

The detailed method EN ISO 52022/3 calculates all of the energy flows created by the combination of glass and shading. It provides a far more accurate assessment and is important for calculations of advanced shading materials where the performance is under-estimated by the simplified method.

Which one should be used?

For comparison of the effect of different types of shading or types of material the simplified method provides a guide to the performance level that is required. For a more accurate assessment for advanced modelling the detailed method should be used.

For the simplified method there are 5 default glazing types (a-e) and for the detailed method 3 types (f-h) that use more accurate spectral data for the glazing. For detailed modelling the spectral data from the manufacturer for the type of glass to be specified should be used.

Reference glazing types

As the type of glass being used will affect the performance of shading products, we need typical glazing types in order to compare. That is the effect of the shading will be different for example if the glass is single rather than triple glazed.

So that we can compare performance of shading we have reference glazings that are typical glazing types that are identified as types a-h. They are also referred to as default values, that is, they are typical values used when you do not know the exact performance of the glazing to be used.



This is a measure of solar heat gain through glazing. Also called solar factor, g-value is the measure of the total energy passing through the glazing when exposed to solar radiation. It is the sum of two values: the solar transmittance, Ts, which is the heat absorbed by the glass and re-radiated as long-wave radiation inwards and Qi the secondary internal heat transfer factor. Qi is where the glass absorbs some of the energy and converts it to long wave heat some of which is radiated back out and some radiated into the room. Qi is the amount absorbed and radiated into the room. The g value is also called the Solar Factor.



When the g-value of the glazing is combined with the value of the shading, this is the Gtot value. A simplified method of calculating that value is described in EN ISO 52022/1 and is also the recommended procedure of EN ISO 14501 for calculating the solar energy transmittance of complex glazing (glass and shading figures combined). For an accurate assessment for building modelling the more accurate calculations of the detailed method in EN ISO 52022/3 should be used.



This measure refers to the fraction of visible light transmitted into a room. As with the g-value, with a shading device, we have to consider the measure of the glass and shading in combination.

Tvtot (Tv or Tvis)

This should be the symbol for the Tv value of the glazing combined with shading but in the standards the value for both is Tv. For clarity it is usual to describe this value as Tvis. The value is between 0 and 1, where 0 means no light is transmitted and 1 means all visible light is transmitted. A Tv value of 0.25 means 25% of light is transmitted.



U-value is a measure of thermal conductance which is the ability of a material to transfer heat by conduction, convection and radiation. All components of a building have U-values for example masonry, insulation materials, plasterboard and windows. The lower the value, the slower the heat loss through the material. Therefore a material with a low U-value is a good insulator. So it is the temperature difference between inside and outside if there is not any solar radiation in W/m²C (watts per metre squared Kelvin).



When the u-value of the glazing is combined with the value of the shading, that is the Utot value. The U-value of glazing is always improved by installing blinds or shutters. Shading can reduce U values of standard low-e double glazing to levels close to those achieved with high specification triple glazing with the added benefit that they can be raised on sunny winter days to admit free solar heat gain. Thus the actual energy benefit is far greater at a significantly lower cost.



The Shading Factor (FC) is the ratio of the total solar energy transmittance of the blind and shading combination divided by the g value of the glazing alone. It is another description of the Gtot value.



The Shading Co-efficient (SC) is a figure that indicates the improvement compared to a single pane of clear glass. Figure 1 shown above shows that a single pane of clear glass has a transmittance value of 0.85. Thus SC = gtot divided by 0.85 example Gtot 0.40 / 0.85 = 0.47. As single glass would no longer usually be considered this value is now rarely used.

A more detailed explanation of these properties can be found in the ES-SO guide book Solar Shading for Low Energy and Healthy Buildings. Download ES-SO pdf

¹ All symbols are shown in Roman script in the standards Greek equivalents are used and can be found in the Glossary


  1. BS EN 410 Glass in Building – Determination of luminous and solar characteristics of glazing, 2011.
  2. EN 14501, Blinds and shutters - Thermal and visual comfort – Performance characteristics and classification, 2021.
  3. EN 14500, Blinds and shutters – Thermal and visual comfort – Test and calculation methods, 2021.
  4. CIE 130-1998 – ‘Practical methods for the measurement of reflectance and transmittance’.
  5. Publication CIE No. 15.2 – 'Colorimetry' (4th edition), Vienna.
  6. EN 673 Glass in Building – Determination of thermal transmittance (U value) – calculation method, 2011.
  7. ISO 10077-1 – Thermal performance of Windows, Doors and Shading Devices – Calculation of thermal transmittance, International Standards Organisation, 2017.
  8. ISO 15099 – Thermal performance of Windows, Doors and Shading Devices – Detailed Calculations, International Standards Organisation, 2003.
  9. BS EN 13125 Shutters and blinds – Additional thermal resistance – Allocation of a class of air permeability to a product, 2001.
  10. EN ISO 52022/1 – Energy performance of buildings -- Thermal, solar and daylight properties of building components and elements -- Part 1: Simplified calculation method of the solar and daylight characteristics for solar protection devices combined with glazing 2017.
  11. EN ISO 52022/2 – Energy performance of buildings - Building and Building Elements - Thermal, solar and daylight properties of building components and elements - Part 2: Explanation and justification 2017. 
  12. EN ISO 52022/3 – Energy performance of buildings - Thermal, solar and daylight properties of building components and elements - Part 3: Detailed calculation method of the solar and daylight characteristics for solar protection devices combined with glazing 2017. 

Obsolete EN standards

  1. EN 13363-1 – Solar Energy and Light Transmittance through Glazing with Solar Protection Devices – Part 1, Simplified Calculation Method, 2007. Replaced with EN ISO 52022/1
  2. EN 13363-2 – Solar Energy and Light Transmittance through Glazing with Solar Protection Devices – Part 2, Detailed Calculation Method, 2005 Replaced with EN ISO 52022/3


Latin Terms & Greek Symbol Equivalents in Standards

Term Description Variants Symbol
gtot Total solar energy transmittance of the window   Rate expressed as 0.00 to 1.00
g Solar energy transmittance of the glazing   Rate expressed as 0.00 to 1.00
Tvis Total visible transmittance Visible = Light (may be replaced by) τv (%)
Ts Total solar transmittance of the fabric (considered as same for window facing side and room side) Solar = Energy (may be replaced by) τe (%)
Rs f Total solar reflectance of the window facing side of the fabric Solar = Energy (may be replaced by) ρe (%)
Rs b Total solar reflectance of the room side of the fabric Solar = Energy (may be replaced by) ρ’e (%)
Rvis f Total visual reflectance of the window facing side of the fabric Visible = Light (may be replaced by) ρv (%)
Rvis b Total visual reflectance of the room side of the fabric Visible = Light (may be replaced by) ρ’v (%)
Glz ID Standard Glazing g Tvis U(W/m2/c) Ts Rs_f Rs_b Avis_f Avis_b
1 EN ISO 52022/1 A: Clear single glazing (4mm) 0.85 0.90 5.80 0.83 0.08 0.08 0.08 0.08
2 EN ISO 52022/1 B: Clear double glazing (4-12-4) air filled 0.75 0.82 2.90 0.69 0.14 0.14 0.15 0.15
3 EN ISO 52022/1 C: Double glazing low-e in position 3 (4-16-4) 90% argon filled 0.59 0.80 1.20 0.49 0.29 0.27 0.15 0.10
4 EN ISO 52022/1 D: Solar control glazing low-e in position 2 (4-16-4) 90% argon filled 0.32 0.44 1.10 0.27 0.29 0.38 0.43 0.38
5 EN ISO 52022/1 E: Triple glazing low-e in positions 2 & 5 (4-14-4-14-4) 90% argon filled 0.55 0.73 0.80 0.50 0.22 0.23 0.16 0.16
6 EN ISO 52022/3 F: Double glazing low-e in position 3 (4-16-4) 90% argon filled 0.64 0.82 1.1 0.58 0.28 0.27 0.12 0.12
7 EN ISO 52022/3 G: Solar control glazing low-e in position 2 (4-16-4) 90% argon filled 0.33 0.70 1.0 0.31 0.37 0.45 0.11 0.16
8 EN ISO 52022/3 H: Triple glazing low-e in positions 2 & 5 (4-12-4-12-4) 90% argon filled 0.53 0.74 0.7 0.47 0.32 0.32 0.16 0.16