CWCT Testing

How does CWCT help architects specify rainscreen cladding systems?

16th February 2023

In our latest blog we look at how the Centre for Window and Cladding Technology (CWCT) is a useful resource for anyone involved in the design, specification and construction of building envelopes.

Established in 1989 and now with over 350 members, the research and guidance carried out by the CWCT offers important benefits to the construction sector. As a company that designs and manufactures rainscreen cladding it is important to us that we are aligned with the CWCT’s industry standards. Here we ask a series of questions that sheds light on how CWCT can help architects:

What is CWCT?

The CWCT provides independent test standards for cladding and glazing manufacturers. The standards developed by CWCT provide important and independent benchmarks for rainscreen panel design and performance that are used throughout the industry. Ultimately, CWCT is an information provider to a wide range of designers, specifiers, manufacturers, and contractors in the construction sector.

How does CWCT help architects?

Specifying cladding that has undergone CWCT testing is the most effective way to ensure that it is fit for purpose and achieves a high-quality building envelope. The CWCT ‘Standard for systemised building envelopes’ provides a framework for specifying rainscreen cladding, along with an architects and specifiers checklist that indicates which information will change from project to project. This covers; Internal and external environment, air permeability and water tightness, amongst others. With a growing focus on building performance and safety, more specifiers and clients now have an expectation that the cladding panels are compliant. With CWCT standards and guidance. Combined with good design, manufacturing and installation, CWCT testing provides architects with peace of mind that your client’s building will perform as expected over the long term.

Where does CWCT sit in relation to British Standards?

CWCT standards are not a replacement for Building Regulations but provide guidance on a wider scope of façade elements. Specifically, CWCT has developed a robust framework for the weather tightness of a building envelope that encompassed performance standards for wind resistance, impact resistance and airtightness.

Who uses CWCT standards?

A growing number of architects and designers use CWCT standards, along with other project partners such as the cladding manufacturer, contractors and installers as well as those involved in the ongoing running of the building. Building services engineers also regularly refer to CWCT standards because they know that the building envelope can influence the overall energy performance. In addition, structural engineers are required to consider building and façade movements and cladding loads, and here again CWCT provides important guidance. Main contractors and installers often prefer it when, like ours, the cladding system has been through CWCT testing because they know it will perform. They also know that, where required, their team will have been trained by us in the correct installation and maintenance of the façade. Insurance companies refer to CWCT guidance and standards, too, when assessing their client’s premises because the guidance and standards inform them of the building’s performance and ability to withstand severe weather conditions.

What does CWCT testing cover?

CWCT has developed a robust framework for testing the weather tightness of a building envelope including:

  • Air leakage testing – Used to determine the air permeability of the envelope. Whole building air leakage test required by Part L of the Building Regulations (England and Wales).
  • Water penetration testing – Tests the watertightness of the building envelope under a uniform static pressure. Site testing used for confidence in workmanship and design.
  • Thermal performance testing – Thermal imaging is used to identify any thermal bridges where air may leakage from the building interior may occur. In addition, cladding surface temperatures are measured to provide information on thermography and what can be done to rectify any issues identified.
  • Impact testing – The hard body and soft body, testing method is used to categorises the risk level associated with a cladding system.
  • Wind testing – Wind load resistance testing applies separate positive and negative wind pressures to the façade. Positive pressure simulates the panels being pushed back against the wall by the force of the wind. Negative pressure applies suction to the panels, which can occur as wind forces its way around and alongside buildings. Systems are tested to ensure they meet serviceability and safety load requirements.

CWCT has written standards on curtain walling, walls with ventilated rainscreens as well as Slope glazing.

Which Proteus cladding has undergone CWCT testing?

The Proteus HR, GL,, CX & SR systems have been  successfully tested in line with CWCT Standard Sequence B: Air permeability; Water Penetration; Wind Resistance (Serviceability & Safety); Impact.

What else does CWCT test for?

CWCT testing also looks at the mechanical build-up of the cladding, plus servicing and maintenance requirements. This latter is an important consideration because it informs the architect and their client of the ongoing running costs of the building. It covers many aspects of the façade, for example, ease of access to services behind the panels in which we use the design of easily dismantlable individual panels.

How do I know if the rainscreen cladding systems has been tested?

Building envelope and cladding systems that have been tested by CWCT will have a test report. To be sure that a rainscreen cladding has undergone CWCT testing, always ask your supplier for proof of compliance and details of tests carried out.

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