The TUC Headquarters is a listed building in Great Russell Street, Bloomsbury, London, built in 1959. It contains a Conference Hall located under a courtyard in the centre of the building. Its roof consists of glazed hexagonal roof lights set into elaborate leadwork upstands and gutters. The TUC report that it has leaked since the time it was first built. English Heritage stipulated that the existing roof must be retained, given its importance as a strong feature of the original architecture.
To resolve this problem, the approach we took was to construct a protective glass skin, slightly above and independent of the existing glazed roof, leaving this totally intact. The existing glazing was cleaned and made good prior to the installation of the new glass rain shield.
The new glass covering is made of colourless low-iron glass, without the usual green tint of normal float glass. It is toughened and lightly acid washed to give a slight degree of diffusion to views through the new surface to the existing roof below. The original hexagonal pattern remains clearly visible and is echoed in the geometry of the new glazing. Supports are machined in stainless steel and include spherical bearings to minimise the transfer of bending stresses from support points into the glass. The upper faces of fixings are flush with the glass surface.
The aim of our approach was to respect the existing while offering a minimal and elegant solution to the problems of water penetration which the TUC has suffered for decades.
While awaiting the opportunity to install the new glass roof, a very low cost temporary cover was required. We designed and commissioned the fabrication of an air-supported cover in translucent agricultural polythene, stabilised by very low air pressure and restrained by a network of nylon ropes anchored to the perimeter. Since the major tensile forces are taken by the ropes, this allowed the use of a very inexpensive membrane of relatively low tensile strength and kept a low profile to allow views out of the offices around the courtyard. Fabricated and erected in three weeks, the structure kept the roof dry for approximately a year and maintained the natural light levels in the hall below.