Saint Paul’s Cathedral, a heritage listed building, has a history of soil movements resulting in the de-stabilisation of the buildings’ stone walls. The William Street front wall had moved to the extent that the roof purlins near the ridge were no longer seated in the wall. Plans from 1986 indicated an attempt to stabilise the moisture regime under the building by constructing a walkway and cut-off wall to perimeter however this was unsuccessful, possibly due to the presence of an underground stream bed that passes under the cathedral.
To control movements of the front wall so as not to risk damage to the stained-glass windows and to limit any further outwards displacement of the purlins from the wall, the solution adopted was to provide a temporary propping frame to the outside wall. As part of this work, the northern end naïve/aisle arches were propped and the exterior stained-glass windows to the east and west walls were removed for safe storage.
Survey monitoring pins were installed in the wall to allow the movement of the wall to be recorded over a period of years to determine the successfulness of the propping and assess the risk of re-installing the east and west wall leadlight windows.