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Curtain walling - General cladding warranty requirements

The below guidance is taken from V13 of Premier Guarantee Technical Manual and outlines the requirements for warranty sign off when using curtain walling.

 

Further guidance on warranty technical standards when using curtain walling systems can be found in our free webinar 'Curtain Walling - Warranty standards and guidance' – follow the link below to register to access this training.

Curtain walling systems should have third-party certification confirming satisfactory assessment, and comply with the requirements of the CWCT Standard for Systemised Building Envelopes, including the following sections:

 

  • Part 1: Scope, terminology, testing and classification
  • Part 2: Loadings, fixings and movement
  • Part 3: Air, water and wind resistance
  • Part 4: Operable components, additional elements and means of access
  • Part 5: Thermal, moisture and acoustic performance
  • Part 6: Fire performance
  • Part 7: Robustness, durability, tolerances and workmanship
  • Part 8: Testing

 

The CWCT Standard provides detailed guidance on performance and testing.

 

Accounting for movement

 

Dead and live loads should be transferred safely to the building structure without undue permanent deformation or deflection of any component.

 

Imposed loads should be calculated in accordance with BS EN 1991. Movement should be accommodated without any reduction in performance.

 

Fixings and supports should be designed to accommodate specified loads and take account of the product manufacturer's recommendations.

 

CE marking is to be provided for all curtain walling covered by EN 13830 in buildings constructed after July 2013, and will therefore include the following curtain wall types:

 

  • Stick construction
  • Unitised construction
  • Double skin walls
  • Structural sealant glazing
  • Bolted glazing

 

The completed system should incorporate cavity barriers and firestops and resist the spread of fire in accordance with the relevant Building Regulations.

 


Water tightness


The completed curtain wall system should resist the passage of water to the inside of the building allowing free drainage, not trapping water and should have:

 

  • External and internal air and water seals
  • Drained and ventilated glazing rebates

 

Sealants should be specified in accordance with BS 6213 or BS EN 15651 and the performance determined by BS EN 11600 and the manufacturer's recommendations.
The system should be designed to minimise the risk of surface and interstitial condensation by the use of thermal breaks and a continuous vapour control layer. It should be designed to resist the passage of airborne and impact sound within the building with particular attention given to flanking transmission at:

 

  • The edges of separating floors
  • The outer edges of separating walls
  • The outer edges of partition walls
  • The junctions with roof constructions and parapets

 

Where curtain wall members run uninterrupted past floor slabs and partition walls, consideration must be given to structure-borne sound (impact sound).

 

The system should comply with BS 7671 requirements for electrical installations for electrical continuity and earth bonding, where it is required to form part of a lightning protection system it must be designed to comply with the requirements of BS 6651.
The risk of bimetallic corrosion should be avoided through the isolation of dissimilar metals. Fixings and finishes to curtain walling must take into account the location and corrosion category to ensure corrosion is avoided. Aluminium components must be robustly isolated from cementitious products to mitigate corrosion.

 

The curtain wall system should not include materials liable to infestation attack by micro-organisms, fungi, insects or vermin.

 

Packing of brackets to achieve surface tolerance is only permitted in accordance with the manufacturer's recommendations, and shall not exceed the maximum depth stated in the designer's calculations.

 

All packers for brackets supporting or restraining the curtain wall must be metal.

 

 

Testing


The curtain wall system will have either been tested and provided with a classification given in BS EN 13830, or if the curtain walling is of a custom design, it would be tested to an appropriate standard of CWCT sequence A or B testing by an independent UKAS accredited test facility to ensure that the system meets or exceeds the weather performance classification for the building taking into account the design parameters and project location.

 

Pull-out or destructive testing of anchors should be carried out in accordance with BS 5080 and the Construction Fixings Association Guidance Note, Procedure for Site Testing Construction Fixings.

 

The number of fixings to be assessed must be agreed on a project by project basis, as an understanding of the scope and size of the project would determine the number of fixings tested. In addition, if there are varying types of fixings then each type should be tested. If the fixing is the same but the structure varies, then each type of structure should be tested.

 

BS 5080 requires five tests per type, however if a very large project is proposed, this could be increased to give more assurance on installation, e.g. every floor, one per side (e.g. North/East/South/West). The scope and number of tests must be agreed with the warranty surveyor at the commencement of the project, to allow sufficient time for testing to be planned in advance and made available to the warranty surveyor when completed.

 

Site testing for water penetration of the joints to windows and doors in accordance with the CWCT test methods is recommended to check the site workmanship of the building envelope as constructed. See CWCT Technical Note No. 41 for guidance on site hose testing.

 


Tolerances

 

Design should allow for the line, level, plumb and plane of the completed curtain wall to be within the acceptable tolerances of:

 

  • Line: +/-2mm in any one storey height or structural bay width, and +/-5mm overall
  • Level: +/-2mm of horizontal in any one structural bay width, and +/-5mm overall
  • Plumb: +/-2mm of vertical in any one structural bay width, and +/-5mm overall
  • Plane: +/-2mm of the principle plane in any one storey height or structural bay width, and +/-5mm overall