This project involved major structural alterations to the existing assembly hall whilst preserving as much of the historic fabric of the building as possible. The project provides the school with new performance and teaching spaces.
The main structural works involved the removal of the existing hall floor (and earlier courtyard below) and the excavation of material below the floor to a depth of over two metres. To achieve this excavation, underpinning was required to the main walls and a new reinforced concrete retaining wall was constructed adjacent to the historic stone façade of the building.
The existing steel columns within the hall were replaced with longer sections to accommodate the increased internal volume of the space. A new, full-height, retractable, acoustic partition was installed to the east and west sides of the hall. To accommodate the new acoustic partitions, the roof support columns in two locations had to be removed and replaced with steel girders spanning the full width of the hall. The girders also provide support to the heavy acoustic partitions in their open and closed positions.
The final and most difficult structural alteration was to form the new stair voids which provide access at the east and west end of the basement. A central vaulted basement ceiling was removed while retaining the vaults on either side. This was achieved by inserting tension rods to tie back the two adjacent vaults while reinstating part of the existing floor above.
A new, cantilevered balcony was installed on three sides of the hall. The balcony was formed in steel with a concrete deck to the east and west ends of the hall. At the south end, the balcony floor is in timber supported on steel. Careful monitoring of the existing structure was carried out throughout the works to ensure that movement was kept within acceptable tolerances and to ensure that loads were transferred safely from the temporary to the permanent supports.