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A Tested Systems Approach to Pre-Cladding

Is there such a thing as ‘pre-cladding’? The reality that the architectural and construction industry now faces, in the aftermath of the Grenfell Tower disaster and in the wake of leaky-buildings, is that pre-cladding and cladding are inseparable. 

For Pacbld (Pacific Build Supply Ltd) the ‘pre-cladding’ element or sheathing is Pacbld RWU (rigid wall underlay).

As E2 succinctly notes in 2.3 ‘Systems versus Materials’: “materials used to construct the building envelope shall be designed as a complete cladding system rather than as separate items."

This concept is clearly evidenced in the extensive testing program for Pacbld Rigid Wall Underlay that Pacbld has conducted over the last three years, which included:

  • AS/NZS 4284 ‘Testing of Building Façades’, for XpressClad PX40 with Pacbld RWU, achieving a ULS of +/-4.5kPa, and Supplementary Testing to +9.75kPa;
  • P21 ‘Bracing Testing’ for 6mm and 9mm Pacbld RWU;
  • BS 8414 ‘External Wall Fire Propagation Test’ for XpressClad PX40 with Pacbld RWU, achieving a BR135 classification;
  • AS 1530.4 ‘Fire Resistance Test’ for XpressClad PX3-0 with Pacbld RWU, achieving a 120/120/120 rating;
  • AS/NZS 4284 ‘Testing of Building Façades’, for XpressClad PX40 and PX20 with Pacbld RWU, achieving a ULS of +/-5.5kPa.

In all of these, it was clear that the Pacbld RWU is the “backbone” of any cladding system.

Having recently updated the Pacbld RWU manual to reflect the learnings from these tests, it became necessary to re-think how Pacbld RWU is defined: it is the primary weather-resistance barrier, it is also the seismic and structural element, and it is also the key FRR element. This one component performs many of the crucial functions required of a full wall assembly cladding system.

To further enhance the weather-resistance of Pacbld RWU, Pacbld recommends using the Pacbld PSM (peel and stick membrane — or full wall wrap). As a system, this improves the watertightness of the cladding assembly, but also allows for air-moisture in the wall cavity to egress and so removes the potential for long term mould growth.

It is necessary as an industry to think holistically and to design holistically, and not to think of pre-cladding and cladding as separate materials, but instead to think of full wall assembly systems.

View more information on Pacific Build Supply, including contact details.
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