Curtain Walling: Total solar energy transmission

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Categories: Performance : Curtain Walling


The current Product Standard does not include total solar energy transmittance (solar factor, g-value). It will be a requirement of the revised Product Standard.

The determination of the total solar energy transmittance (solar factor, g-value) of translucent glazings should be carried out in accordance with EN 410, or if relevant, with EN 13363-1 or EN 13363-2.

The values calculated are those at normal incidence of radiation and do not take into account the angular dependence of transmission or reflectance of materials. Where glazings with different radiation properties are used in the curtain wall an area-weighted average value should be given.

The calculation includes any shading device in the plane of the wall (parallel to the glazing), ie louvres and blinds. Shading devices such as brise soleil are excluded.


EN 410Glass in building – Determination of luminous and solar characteristics of glazing
EN 13633-1Solar protection devices combined with glazing – Calculation of solar and light transmittance – Part 1: Simplified method
EN 13633-2Solar protection devices combined with glazing – Calculation of total solar energy transmittance and light transmittance – Part 2: Detailed calculation method


Method of test

There is no method of test. Classification is on the basis of calculation.


There is no classification for the radiation properties of the curtain wall. The Product Standard requires the total solar energy transmission to be declared.

CE Marking

The Regulations do not give explicit limits to the g-value of the curtain wall. Solar gains during the summer have to be limited and this is demonstrated by taking the solar gains through the glazing aggregated over the period from April to September inclusive and comparing the result to a reference glazing system. The allowable use of No Performance Determined (npd) is as follows:

Locationnpd allowed
England and WalesProbably not
ScotlandProbably not
Northern IrelandProbably not