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CROSS Safety Report

Inadequate brick ties in gable walls

Report ID: 785 Published: 1 July 2019 Region: CROSS-UK

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Overview

A reporter was called to council houses at four different sites, whose upper triangle of cavity wall brickwork on the gable end had fallen out, due to not being tied into the roof.

Key Learning Outcomes

For construction professionals:

  • Quality assurance and competent supervision on site can help to ensure that the structure is built in accordance with the design

  • Consider introducing a quality management procedure for the inspection of safety critical elements such wall ties and head restraints

For civil and structural design engineers:

  • A lack of, or incorrect use, of masonry ties being installed has been the cause of many wall failures. This can occur particularly on walls zones that are subjected to high wind suction pressures.

  • Ensure the correct wall tie densities and embedment lengths are specified on the construction drawings

  • During site visits look to ensure the correct wall ties are being installed on site and at the required spacings

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When working for a local authority after the Great Storm of 1987, where hurricane force winds caused casualties across the UK, a reporter was called to council houses at four different sites, whose upper triangle of cavity wall brickwork on the gable end had fallen out, due to not being tied into the roof.

In one case, two of the brick triangles had fallen on to a common single storey corridor link between care home blocks, fortunately with no one was on the corridor link at the time. The solution was to rebuild the top triangle and build in ties to new diagonal bracing in the timber roofs, many of which were common rafter and purlin roofs, with no existing diagonal bracing.

During the investigation on one large council estate, it became evident that the top brickwork triangles had no ties between inner and outer skins of the cavity walls. On further investigation, it appeared that the ground floor had ties at the correct centres, reducing to twice the centres at first floor, and none at the top where they had evidently run out of ties. The entire estate was then inspected and around a third of the houses had similar problems, resulting in much remedial tie installation, says the reporter.

During the investigation on one large council estate, it became evident that the top brickwork triangles had no ties between inner and outer skins of the cavity walls

Expert Panel Comments

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A lack of brick ties has been the cause of many wall failures due to wind suction. On older domestic properties this may have been due to the customs of the time. Modern properties should be constructed in accordance with the building regulations and advice from bodies such as the Brick Development Association. On a bigger scale, the lack of embedment of ties contributed to the collapse of a school in Edinburgh and major remedial work to many others. See the Standing Committee on Structural Safety (SCOSS) Alert on Inquiry into the construction of Edinburgh Schools - February 2017.

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