The Edinburgh schools report: A wall tie manufacturer’s perspective
Only “timing and luck” saved the lives of schoolchildren.
This is one of the conclusions of the independent inquiry into the collapse of a masonry wall at an Edinburgh school on 29th January 2016. For anyone involved in the construction industry, the report published in February 2017, has to be a wake-up call.
The wall collapsed at 7:00am when the school grounds were thankfully empty.
The wall tie embedment in the outer leaf was found to be woefully inadequate and, in bad weather, the action of the wind caused the brick cladding to simply pull away from the inner leaf of blockwork, scattering approximately nine tonnes of masonry on the walkway below.
Wall Ties are a critical structural component in masonry wall construction. If wall ties are installed incorrectly, there is high potential that the wall will not reach its designed capacity and in severe cases, like the Oxgangs Primary School, may collapse.
Whilst we can continue to worry about what could have happened on that day, the Construction Industry should collectively breathe a sigh of relief that no one was injured or killed and focus now on what happens next. This in-depth and well-written report will be an uncomfortable read for many, but lessons must be learnt and changes have to be made.
They were not Ancon wall ties used on this particular project, but they easily could have been and the outcome would have been the same. Build quality was the issue. The wall tie manufacturing industry can take solace in the fact that after a comprehensive and independent review of the construction of this and other Scottish school projects, there is no suggestion that product quality was either a cause of the initial collapse or a concern elsewhere.
This is important to our sector and it should provide reassurance to specifiers, contractors and other authorities. Our stringent product performance tests and quality control measures in the UK should be acknowledged.
Reputable manufacturers, like Ancon, CE mark their products to the European harmonised standard BS EN 845-1. This means the performance values declared in our marketing materials are independently verified through extensive laboratory type testing. Most UK manufacturers, like Ancon, also operate ISO9001-compliant quality management systems. Together, these measures ensure our products are ‘fit for purpose’ when they leave the factory.
The report found the collapse was ‘avoidable’, declaring that ‘proper quality control’ during construction would have both identified and rectified the workmanship issues that led to the collapse and put further children at risk at other locations.
There are early indications that the report is having an impact across the industry. It is encouraging for Ancon to see that within a matter of days of the report being published we have been contacted by senior management from leading contractors keen to understand more about wall ties, particularly how best to ensure adequate embedment depth is achieved on site, and how to communicate this information around their organisations.
Ancon has considerable experience and knowledge to share with the industry, and we provided expert guidance to the independent inquiry panel.
We have directed recent enquirers to our wall tie technical literature and relevant online articles such as:
Wall Tie Spacing and Tie Lengths
Ancon is now working with various construction partners on new communication materials to help spread the key messages, particularly on site, to bricklayers and site supervisors.
We must improve awareness of the importance of wall ties, and other masonry support and restraint fixings, and make clear what good and poor installation looks like.
We will continue to expand our information portfolio, so please get in touch with any specific questions and communication requirements.
To confirm, when building masonry cavity walls, contractors should always:
- Check the project specification for type and length of wall tie
- Check the wall tie manufacturer’s technical literature for recommended embedment depth
- Check this embedment depth is achievable on site with the given wall ties, the intended wall build-up and the construction process being employed, before work starts
- Communicate the required embedment depth to all bricklayers on site
- Centre symmetrical wall ties, so equal embedment is achieved in each leaf (or consider longer ties if deeper embedment is required to prevent overbalancing, if one leaf is to be built ahead of the other)
- Maintain cavity width on site
Contact Ancon for more information.
A copy of the full Edinburgh schools report is available from: http://www.edinburgh.gov.uk/schoolsinquiry
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Designed to minimise thermal bridging in masonry cavity walls, the patented Ancon Thermal Windpost (TWP2) from Leviat offers up to an impressive 70% reduction in thermal transmission through the span of the windpost.