Skip to main content

CROSS Safety Report

High winds cause masonry parapet failure

Report ID: 803 Published: 1 April 2019 Region: CROSS-UK

This report is over 2 years old

Please be aware that it might contain information that is no longer up to date. We keep all reports available for historic reference and as learning aids.

Overview

A reporter highlights how exceptionally strong winds caused a fourth-floor level masonry parapet wall with a 1.7m high timber fencing on top of it to collapse.

The parapet overlooked a three-storey light-well that was situated within the confines of the building

At the base of the lightwell was a rooflight into an occupied space. Had the parapet slipped and fallen into the lightwell there could have substantial damage and possibly fatalities.

Key Learning Outcomes

For civil and structural design engineers:

  • Adding to the height of cantilever walls should be carried out with care. If the additional load added is a UDL (like wind), then the bending moment at the base is proportional to the square of the height

  • Be aware that attaching hoardings to walls can increase the windage on them and the walls may not be designed to take the load increase

  • A design check should be carried out on an existing wall or parapet that have attachments added to them

Full Report

Find out more about the Full Report

Our secure and confidential safety reporting system gives professionals the opportunity to share their experiences to help others. If you would like to know more, please visit the reporting to CROSS-UK page.

A building has a roof top plant area above the fourth-floor level. The area is screened by timber fencing of approximately 1.7m above the top of the masonry parapet wall, which is in turn fixed to vertical posts that are secured to the wall. There was no evidence of raking bracing to the screen or support posts.

The parapet is approximately 0.9m high (excluding copings) and overlooks a three-storey light-well that is situated within the confines of the building and is south easterly facing. The parapet is approximately 225mm thick masonry in English bond. It is possibly lime mortar bedded and topped with rolled-top, terracotta, saddle copings.

Strong winds cause parapet to collapse

In 2018, there were exceptionally strong south-easterly winds with gusts of approximately 50+mph (80 km/hr). Under these conditions the wall collapsed, and inspection revealed that the parapet and attached screening had been pushed over. The masonry had failed on the bed joint across almost the whole of its length as shown in Figure 1. The left side of the parapet was a free edge with the right side bonded to a chimney.

Image
Figure 1: failure of brick masonry parapet wall with fencing fixed to top

It is assumed that the action of the strong winds on the screening allowed sufficient pressure to cause the screen and fence to be overloaded. As the wall has little tensile strength, the failure resulted along the bed joint closest to the roof level. At the base of the lightwell was a rooflight into an occupied space. Had the parapet slipped and fallen into the lightwell there could have substantial damage and possibly fatalities.

At the base of the lightwell was a rooflight into an occupied space. Had the parapet slipped and fallen into the lightwell there could have substantial damage and possibly fatalities.

Expert Panel Comments

Find out more about the Expert Panels

Expert Panels comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-UK Expert Panels page.

There is a similarity here to the collapse of a wall in Melbourne Australia in 2013. A 3.2m high advertising hoarding was up to 70cm taller than the ground level free-standing brick wall to which it was added. The wall blew down and three people were killed. There have been other cases where attaching hoardings have increased the windage on walls, which are vulnerable anyway, and have precipitated collapse.

Cantilever design issues

Although this report is about a wind loading failure, it has parallels with CROSS report 620 on balconies. In report 620 the reporter was concerned that the balcony designer had anchored their cantilever to some inner structure without verifying that it was adequate for the task. Every structure must be looked at as whole. Danger lurks at interfaces between units or at interfaces between divided responsibilities as highlighted in report 789 .

Adding to the height of cantilever walls must always be taken seriously as, if the load is a UDL (like wind), the bending moment at the base is proportional to the square of the height. It is not known if there was a designer in this instance but there should have been. If there had been casualties or fatalities, the responsibility would have come back to the owner of the premises.

Share your knowledge

Your report will make a difference. It will help to create positive change and improve safety.

Our secure and confidential safety reporting system gives professionals the opportunity to share their experiences to help others.