Alastair Soane, Director of Structural Safety, said:
“Ceilings are usually hung from structures above and it is the fixings which can give way.
“Older plaster ceilings which have not been inspected for many years may be particularly vulnerable.Two examples of older plaster ceiling collapses can be found in the CROSS database:The Apollo Theatre Ceiling collapse and Fibrous plaster ceiling features.
“The reasons for the Piccadilly Theatre ceiling collapse on 6 November are not known. No doubt there will be detailed investigations taking place and in due course there will be lessons to be learned. Structural-safety will pass these on through their newsletters and alerts so that others may learn.
“Meantime it is recommended that theatre owners, and those with similar venues, exercise vigilance and have their ceilings checked by Chartered Structural Engineers.”
Michael Holden, Chairman of the Institute of Theatre Consultants and a member of IStructE’s History Study Group said:
“Fibrous plaster is a decorative material extensively used in older theatres and historic houses. It is usually made in moulded pieces on the bench and secured in place on sub frames to form the ceiling.
“Traditionally this fixing was hessian or string ties, daubed with plaster to protect them. More recently galvanised wire is used as the tie. Ceiling collapses are rare but in fibrous plaster usually the result of the failure of ties by water penetration of the tie and the rot of hessian or string, or the rot of the thin timbers in the plaster moulding around which a tie is secured.
“The Apollo Theatre ceiling collapse of 2013 has led to a detailed consideration of such ceilings and inspections of similar buildings. Some historic houses and theatres have undertaken preventative measures, by adding suspension ties where desirable.
“The Piccadilly Theatre dates from 1928 and has been refurbished several times since then. The failure appears from a photograph to be over the upper balcony in a flat (and possibly non-fibrous plaster) ceiling bed.
“There are anecdotal reports of the sound of running water in the ceiling void shortly before the collapse and that might indicate a water incursion above the ceiling, though curiously there are no reports of people getting wet. It was not raining at the time, but scaffolding suggests that work is going on to the exterior of the building.”
A detailed investigation is awaited.
Chris Boydell MIStructE said:
"We will have to await the results of an investigation to understand why this collapse took place.
"Theoretically ceiling voids are benign environments, albeit subject to a wide thermal range. However, the environment can change suddenly if there is water leakage, either through the roof or due to some form of inundation. These factors cause creeping deterioration of the structure and ceilings or can create a failure where there is little or no notice.
"The structural safety of London’s West End theatre ceilings should have improved over the last six years, since the 2013 Apollo Theatre ceiling collapse.
"Westminster City Council and the Association of British Theatre Technicians (ABTT), working with other parties, agreed a guideline for regular inspections by structural engineers and plaster specialists, commonly referred to as ABTT guideline 20.
"The inspection would involve a structural engineer assessing the roof structure and the secondary or tertiary structure that carries the ceiling. The plaster specialist is responsible for assessing the condition of the plaster ceiling and the way it is fixed to the supporting structural elements. Together they should prepare a certificate of satisfactory condition that can also be used for licensing purposes. The guideline states that such inspections should be undertaken annually.
"In addition many theatre operators have improved the accessibility and cleanliness of ceiling voids, some undertaking comprehensive ceiling strengthening and improvement as part of refurbishment work. Most prudent operators have restricted unapproved access to the ceiling voids and appointed ceiling champions or managers with responsibility for condition, inspections and maintenance."