CROSS Safety Report
Cladding panel blown off
This report is over 2 years old
A reporter has become aware of an incident where a decorative cladding panel fell from an upper level of a multi-storey building in high winds.
Key Learning Outcomes
For construction professionals
Quality assurance and competent supervision on site can help to ensure that cladding systems are installed in accordance with the design
Consider introducing a quality control procedure for the inspection of safety critical fixings for cladding systems
Where complex cladding systems are being installed it is good practice that those undertaking the work have specific training for the required system
For civil and structural design engineers:
The cladding design and installation should be given the same degree of attention as the primary structure during both design and construction to improve safety, reliability and longevity
Give attention to the whole design of cladding systems and the safety-critical aspects of their fixings and anchors
If possible, attend site to inspect the installation of cladding systems and their fixings
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This reporter has become aware of an incident where a decorative cladding panel fell from an upper level of a multi-storey building in high winds. The panel was of a resin concrete type which can be manufactured in sizes from approximately 500mm to around 1000mm with varying thickness. The panel weights are typically in the range 5–15kg. It was fixed to the building via horizontal aluminium cladding rails top and bottom of each panel, located in thin, relatively shallow slots about 12mm deep.
Subsequent investigations found that defective workmanship in the cladding rail installation was largely to blame for the panel becoming detached, with missing fixings being the principal cause. The review also found that the installation process required very fine tolerances (e.g. to 0.5mm) which can be difficult to achieve under site conditions. The panel manufacture/installation process is covered by a recognised third party accreditation body, but the accreditation does not mention the specific installation tolerances.
Subsequent investigations found that defective workmanship in the cladding rail installation was largely to blame for the panel becoming detached, with missing fixings being the principal cause.
The reporter recommends that anyone contemplating similar installations ensures that those undertaking the work have specific training in the particular installation, are aware of the very fine tolerances. They also advise that there are adequate and comprehensive checks on each element of the installation throughout the erection process.
Expert Panel Comments
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It is unrealistic for site tolerances to be as demanding as those given here which would seem to be more appropriate to factory conditions. For safety, a fundamental question that can always be asked is ‘are you sure that what you thought was being built was actually built?’. CROSS has had numerous cases where the answer was ‘no’ and this is one of them. A precaution is always to make some site inspections.
As a generality, nothing on sites should depend on achieving fine tolerances. Although this, and report 519 (which described how PV panels were blown off a roof), are wind related, the bigger issue is sensitivity to quality of installation. That said, it is important to recognise that high local wind pressures (suctions) can arise at the edges of roofs, and these need to be taken into account in the structural design of fixings for items such as cladding and PV panels.
Some guidance is given in EN1991-1-4 (wind actions) and its predecessor (BS6399-2) but it should be recognised that these provisions relate to relatively simple building shapes. Some experts advocate higher partial load factors to account for uncertainty due to building shape. Some designers specify tethers for non-structural items on roofs to ensure they do not present a hazard to the public should they become detached from their fixings.
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