Guidance for specifiers > Windows

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Fitness for purpose

The presence of a CE Mark on a product does not imply fitness for purpose. CE Marking does not take away from the Specifier the responsibility to specify appropriate products capable of deleivering the required performance.

CE marking of some performance characteristics is on the basis of classes of performance, for instance watertightness. The Specifier should state which class of performance is required.

CE marking of other performance characteristics, for instance U-value, is on the basis of a declared value. The Specifier should state what value is required.

Guidance on CE marking of performance may be found using the 'performance' button above.

Guidance on appropriate levels of performance for windows in curtain walling may be found in CWCT Standard for systemised building envelopes.


EN 14351-1 covers windows, roof windows and external pedestrian doors

A window is defined as ????????.

A roof window is defined as ????????. There is no European Standard for slope glazing and no ability to CE mark slope glazing.

Under the Construction Projects Regulation there is an axception to CE marking for one-off components that are hand crafted (Not constructed from a system of parts). This may apply to some windows that are hand crafted from timber as 'art windows' or part of a restoration project

What performance is CE marked?

When a Specifier uses a wholely performance based specification then the CE Mark should declare performance equal to or exceeding the requested performance.

When a Specifier selects or details elements of the window such as the glass the CE Mark will declare the performance of the wall as built, these may not be the values anticipated by the specifier.

Window assemblies

A window assembly may comprise:

  • Windows side by side (for instance ribbon glazing)
  • Windows assembled to form a bay window
  • More copmplex assemblies of windows to form screens(Sometimes called window wall)
  • EN 14351-1 states that for windows assembled as screens the joining profiles should be included in testing and assessment of the window. However most windows are tested as stand alone components.

    For a glazing screen or other window assembly the following rules apply:

  • The watertightness class of performance will be that of the lowest performing component (window or joining profile).
  • The air permeability will be calculated from the air permeability of the different components and interfaces
  • The wind performance will be that of the lowest performing component (Note that structural calculations may be required for some configurations)
  • It follows that if the joining profiles have not been tested the window assembly cannot be CE marked.

    Windows in curtain walling

    Windows in curtain walling are CE marked in accordance with EN 14351-1. The remainder of the curtain wall and the window / wall interface are CE marked as curtain walling in accordance with EN 13830. This recognises that the fixed parts of the wall will have higher air, water and wind performance than opening windows. Note that other performance such a thermal transmission is consider for the whole wall including windows.

    The architectural secification will have requirements for the wall as a whole to cover air, water and wind performance. It may also have requirements for window operation.

  • The overall air permeability is established by adding the air permeability through the windows and through the fixed part of the wall. The Specialist Contractor may be requested to give a separate declaration of the overall air permeability.
  • The overall water leakage will be determined by the lowest performance of any window or the fixed part of the wall.
  • The overall wind resistancewill be determined by the lowest performance of any window or the fixed part of the wall.