CROSS Safety Report
Thin stone cladding problems
This report is over 2 years old
A reporter was involved with two investigations which uncovered problems with thin stone cladding.
Key Learning Outcomes
For construction professionals:
Any alterations to connection details such as cladding support systems should be approved by the design engineer
Quality control and competent supervision on site can help to ensure that cladding systems are built in accordance with the design
The cladding design and installation should be given the same degree of attention as the primary structure to ensure safety, reliability, and longevity
For civil and structural design engineers:
Routinely raise the risks associated with unapproved alterations to contractors and the wider project team
Consider attending site to inspect the installation of cladding systems and their fixings
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A reporter was involved with two investigations which uncovered problems with thin stone cladding. In both cases the cladding had been installed by the same specialist sub-contractor, and it was found that the stone masons had deliberately cut the dowels to make it easier to install the cladding.
In one instance the issue came to light after a stone fell due to storm winds (thankfully not injuring anyone), and in the other a stone was dislodged by the window cleaner (rope access) highlighting the defect. On the latter building, the stone cladding extended to ten storeys and rectification required stripping and rebuilding.
Expert Panel Comments
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A standard category of CROSS report relates to inadequate fixings and these amount to 20% of the total. This is one more example. The Edinburgh schools’ (Inquiry into the construction of Edinburgh Schools - February 2017), problem was also due to fixings not meeting design intent. As in report 627, the consequences of failure were potentially severe. There are just too many reports of contractors altering designs to ‘make installation easier’ and thereby creating danger.
There are too many reports about claddings and two issues are to be considered. Firstly, the design of fixings that appear rational on a drawing but prove to be difficult to install and align in practice. Furthermore, such fixing systems lack the robustness and redundancy that are normal in structural engineering.
Secondly the lack of training and onsite control of sub-contractors. With the increased use of large cladding panels, of any material or combinations of material, on multi-storey building this type of failure is likely to become increasingly common and given the height from which panels may fall the potential consequences are severe.
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