Curtain Walling: Air Permeability

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Categories: Performance : Curtain Walling


The air permeability is assessed by either:

  • Testing as an Initial Type Test
  • Testing as a project test
  • Calculation from the results of a test
  • The values obtained by testing or calculation and declared on the CE Mark relate only to the fixed parts of the curtain wall. Windows and doors inserted in the curtain wall are tested, classified and CE Marked as separate products. Air permeability through the interface joints between the curtain wall and any window or door insert is considered to be part of the curtain wall air leakage; it is included in the air permeability value declared on the CE Mark.

    Air permeability may be given as either:

  • air leakage per unit area (m3/m2/hr)
  • air leakage per unit joint length (m3/m/hr)
  • The Specifier will be interested in air leakage per unit area. The air leakage per unit joint length is useful when calculating air leakage for different wall configurations. It is useful when Initial Type Testing to record both results.

    Where air permeabiliy results from an Initial Type Test is given per unit length, the classification may be used directly for CE Marking.

    Where air permeabiliy results from an Initial Type Test are given per unit area it is necessary to consider the ratios of joint length to unit area of the test specimen and the project wall to determine the classification for CE Marking. Unlike the current Product Standard; the revised Standard will give explicit rules for determining the classification for CE Marking.


    EN12152Curtain walling - Air permeability - Performance requirements and classification
    EN12153Curtain walling - Air permeability - Test method
    EN12207Windows and doors - Air permeability - Classification


    Method of test

    A large specimen of curtain waling should be tested in accordance with EN 12153. The revised Product Standard EN 13830 will give a clearer definition of suitable specimen configurations and sizes in an Informative Annex. Full details of specimen requirements are included in the testing section. Testing a specimen to the requirements of CWCT SSBE will meet the current and future requirements of EN 13830.

    The revised test specimen confguration includes a window insert. However, the project wall will often have different windows and doors than those included in the Initial Type Test. Air leakage through the window/wall interface will be similar if the gaskets, beads and other fixing details are similar and the window frame is not greatly different in stiffness.


    For guidance on appropriate classes of air permeability performance for use in the UK refer to CWCT SSBE. The following classes are recognised across Europe:

    Based on overall area

    ClassMaximum pressureAir permeability
    A1150 Pa1.5 m3/m2/hr
    A2300 Pa1.5 m3/m2/hr
    A3450 Pa1.5 m3/m2/hr
    A4600 Pa1.5 m3/m2/hr
    AE>600 Pa1.5 m3/m2/hr

    Based on joint length

    ClassMaximum pressureAir permeability
    A1150 Pa0.5 m3/m/hr
    A2300 Pa0.5 m3/m/hr
    A3450 Pa0.5 m3/m/hr
    A4600 Pa0.5 m3/m/hr
    AE>600 Pa0.5 m3/m/hr


    CE Marking

    UK Regulations require an overall building air leakage rather than placing a specific requirement on the curtain wall. However, it can be argued that the information is required for the building designer to establish the overall performance of the building. The allowable use of No Performance Determined (npd) is as follows:

    Locationnpd allowed
    England and WalesProbably not
    ScotlandProbably not
    Northern IrelandProbably not