CROSS Safety Report
Precast concrete canopies in housing
This report is over 2 years old
A reporter warns that precast concrete cantilever canopies which are slender and monolithic with lintels over entrance doorways can be vulnerable to sudden collapse.
Key Learning Outcomes
For building surveyors and engineers:
- Draw attention to the risks in cases where such a canopy may not have been included in the instructions for the survey. This is a form of 'falling masonry' risk.
For homeowners and local authorities:
Be aware of this type of failure. If you are concerned with a canopy or similar element that is showing signs of deterioration, engage a suitably qualified engineer to carry out a structural inspection and assessment.
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A reporter wants a warning passed on to those undertaking surveys of houses. They say that precast concrete cantilever canopies which are slender and monolithic with lintels over entrance doorways, particularly those constructed in the 1960's and 70's, can be vulnerable to sudden collapse.
They are aware of a number of such failures and have investigated one case where a child was crippled for life when such a canopy snapped and fell on her. The reinforcement is vulnerable to corrosion and may in some instances be deficient, whilst the concrete may contain chlorides and/or be of poor density.
A competent building surveyor should generally seek an engineer's views; often however valuation surveyors are not looking for latent defects and will usually caveat their reports. Engineers and surveyors should ensure that they routinely draw attention to the risks in cases where such a canopy may not have been included in the instructions for the survey. This is a form of 'falling masonry' risk.
Expert Panel Comments
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Report 118 gave an example of a major failure brought on by concrete degradation (Boulevard de la Concorde). Housing units are not likely to have received the attention that such bridges receive, and so if anything, are more at risk from concrete degradation, which is usually, linked to reinforcement corrosion.
As this report shows the consequences can be horrifying. A competent surveyor ought to look for signs of degradation assisted by a knowledge of areas likely to be at risk. CROSS is grateful for this warning and is keen to hear from individuals, local authorities, housing associations and the like of their experiences in similar situations.
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