Initially it had been proposed to dismantle, repair and rebuild the entire structure, but this would have been prohibitively expensive. Ramboll proposed a more cost-effective solution, requiring the removal of the glazing system only, so that work to the structural frame could be performed from scaffolding with minimal deconstruction. Ramboll developed the schedule of repair by a regime of prompt inspection of the metalwork in the period between the existing coatings being removed and the new system being applied. The majority or repairs were successfully undertaken insitu and dismantling successfully kept to a minimum.
Assessing, restoring and repairing
As newly appointed lead engineering consultant Ramboll produced the initial condition report, identifying corrosion from failure of existing paint systems to metalwork as the primary defect. Close inspection by engineers on mobile elevating work platforms (MEWPs) revealed the full extent of the damage to the ironwork.
The detailed report allowed for the creation of a schedule of necessary repair works, planning contingency for change once the existing paintwork was removed from the structural frame.
Centre block high-level walkway plates were in a severely corroded state and had to be disposed of and replaced. The main reason was that water had got into the interfaces with supporting steelwork. We overcame a repeat of this by offsite painting of new plates and using a rubber bearing on top of the site-painted support structure.
To facilitate the repair of the frame, the 1980s aluminium-framed glazing system had to be removed, refurbished and stored until it could be reinstated. To ensure fit during the reinstatement every element was given a unique ID, scheduled with its location and double-tagged.
Two key objectives of the project were to improve daylight and ventilation available to the specimens. We discovered that the condition of the old glass was such that its transparency could not be restored to acceptable levels. The glass needed to be replaced throughout, with the old glass sent for recycling. The opening lights used to ventilate the building and prevent overheating were restored to operation. We designed solutions for providing more control over the heating and ventilators, with the key lights now controlled via the new building management system.
With maximising public access a critical objective, we conducted a review of the architect's and MEP engineer's layouts for improving access throughout the glasshouse, for RBG staff. The Ramboll team identified further work necessary to deliver on the original plans. This included reinforcing concrete services trenches below the pathways in the central block, and altering the basement layouts in the north and south octagons.