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CROSS Safety Report

Non-structural roof soffit linings - failure

Report ID: 462 Published: 1 January 2015 Region: CROSS-UK

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Overview

A reporter has observed the occurrence of compressed fibre cement sheets becoming dislodged from the soffit of several buildings in Australia.

Key Learning Outcomes

For civil and structural design engineers:

  • Ceilings should be given the same degree of attention as the primary structure during both design and construction to improve safety, reliability and longevity

  • Selecting the correct fixings for the given environment and anticipated loads is important to ensure they perform as expected

  • Manufacturer's design and installation information should be used for the scenario in hand. It is unwise to extrapolate design aids beyond the scope for which they were originally intended without approval from the manufacturer.

For construction professionals:

  • Quality control and competent supervision on site can help to ensure that ceilings are built in accordance with the design

Full Report

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The reporter has observed the occurrence of compressed fibre cement sheets becoming dislodged from the soffit of several buildings in Australia. This lining is typically considered to be non-structural but with linings on buildings of 15 or more storeys, the risk of these falling and causing damage to people and property is considerable. Failure typically appears to be in the form of the sheeting pulling over the head of fixing screws.

The reporter believes these soffit linings are typically not being designed by a structural engineer but that installers are utilising the product design information to determine framing and screw spacing. It is apparent from reviewing the product design information available that design tables have been provided for residential structures and conditions. In Australia these are typically categorised as being two storeys or less, so significantly different to conditions being experienced at 15 storeys or more.

The lesson to learn here, says the reporter, is that product design information should be reviewed for applicability to the conditions. If the conditions are outside the stipulated parameters, the product application should be engineered from first principles utilising product capacity information and support from the product manufacturer.

The lesson to learn here, says the reporter, is that product design information should be reviewed for applicability to the conditions

Expert Panel Comments

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This is similar to report 461 which discussed metal cladding blowing in the wind where fixings failed due to wind vibration and it adds to the trend of problems with fixings. The soffit panels in this case are akin to ceiling panels where there are many examples of failure. These are amongst the non-glamorous aspects of design which do not get the attention they need. Generally, the following are areas of uncertainty:

  • The applied loads

  •  The adequacy of the fixings

  • The reliability of installation

The consequences of failure potentially can be dire. A sheet falling from 15 storeys could be lethal. To guard against this, designers, whether working for consultants or for contractors, must appreciate their responsibilities. Redundancy is required and in safety-critical cases, a robust retention solution should be considered. Furthermore, it is always unwise to extrapolate design aids beyond the scope for which they were originally intended.

CROSS-AUS NOTE: It is essential that designers and installers are using manufacturer's design information that is suitable for the scenario in hand. Designers and installers are also reminded of the additional requirements when designing in cyclonic areas as called up in AS1170.2 and the National Construction Code. CROSS-AUS invites your feedback on any similar issues that you have e

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