Glass > Thermal properties
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Principles
The thermal transmittance of the curtain wall should be calculated using the properties of the glass and the emissivities of the surfaces including coatings.
Standards
| EN 673 | Glass in building – Determination of thermal transmittance (U value) – Calculation method |
| EN 12898 | Glass in building. Determination of the emissivity |
Method of test
There is no method of test. Classification is on the basis of calculation.
Classification
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:
| Location | npd allowed |
| England and Wales | No |
| Scotland | No |
| Northern Ireland | No |