Glass > Thermal properties

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Categories: Performance: Glass


The thermal transmittance of the curtain wall should be calculated using the properties of the glass and the emissivities of the surfaces including coatings.


EN 673Glass in building – Determination of thermal transmittance (U value) – Calculation method
EN 12898Glass in building. Determination of the emissivity


Method of test

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


There is no classification of thermal transmittance. The Product Standard requires the U-value to be declared in units of W/m2K.

CE Marking

UK Regulations set out the worst acceptable standards for fabric properties. This value represents the area-weighted average value for all elements of that type. The allowable use of No Performance Determined (npd) is as follows:

Locationnpd allowed
England and WalesNo
Northern IrelandNo