Curtain Walling: Thermal transmittance
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Principles
The thermal transmittance of the curtain wall should be calculated in accordance with EN 12631.
EN 12631 allows for the calculation of a linear thermal transmittance (ψ-value) due to the installation of a window in a curtain wall. It therefore follows that the calculated overall thermal transmittance of the curtain wall should include any windows that are present.
The effects of attachments to the wall, such as brackets for shading devices, whilst not explicitly covered in the scope of EN 12631 should also be calculated with reference to EN 10211.
Standards
| EN 12631 | Thermal performance of curtain walling – Calculation of thermal transmittance |
| EN 10077-2 | Thermal performance of windows, doors and shutters – Calculation of thermal transmittance – Part 2: Numerical method for frames |
| EN 673 | Glass in building – Determination of thermal transmittance (U value) – Calculation method |
| EN6946 | Building components and building elements – Thermal resistance and thermal transmittance – Calculation method |
| EN10211 | Thermal bridges in building construction – Heat flows and surface temperatures – Detailed calculations |
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 |