The Theatre Royal is removing dangerous concrete found in modern flat roofs above its main stage.
Reinforced autoclaved aerated concrete (RAAC) was found in part of the building which houses theatre staff and toilets.
According to planning documents, these are above the left-wing area of the main stage.
An application to remove the roofs says: “The roofs are currently ponding with water due to the RAAC bowing and the current roof felt covering is deteriorating significantly as a consequence and requires replacement before water ingress occurs. The rainwater goods are also in poor condition and require replacement.
Due to the safety concerns of the bowing roof and the discovery of RAAC a temporary crash deck with steel propping has been installed to safeguard the users below from any potential collapse.”
Ambassador Theatre Group (ATG), which owns the Victorian theatre, wants to remove the RAAC and panels and replace them with a new modern roof.
It wants to start carrying out the works starting 16 June, during the theatre’s “dark period” when no shows are staged in the main theatre.
The main stage will be closed, but it is planning a series of family activities under the colonnade called CollyFest.
The theatre has just undergone a multimillion pound refurbishment, which culminated last month in the unveiling of the restored terracotta colonnade on its New Road frontage.
Theatregoers will soon be able to step out onto the balcony above the colonnae from the Royal Circle Bar.
A new entrance has also been created from the theatre foyer into the Colonnade Bar on the ground floor, which has been taken back under theatre management.
The Grade II* listed theatre has been on its current site since 1807.
Crumbling RAAC caused a crisis last summer after scores of schools in which it had been discovered were told not to reopen after a beam collapsed at one.
The concerns led to other public buildings carrying out their own surveys, and several theatres closed as a result in September.
The aerated concrete was used widely in the mid-1950s as a cheaper and more lightweight alternative to conventional reinforced concrete.
