Our involvement in High Sunderland was predicated not by any particular concern about the structural performance of the building but as a sensible expedient, to check that all was well during this first major overhaul of the building.
We were fortunate in having copies of some original construction drawings. This information, proved through targeted opening-up work to confirm its veracity, enabled a good understanding of the existing structure to be established.
The building is a very simple structure: it is a box, having load-bearing walls of timber-stud construction with a flat roof of either timber- or (for longer spans) lattice-steel joisted construction (so-called ‘Stratford joists’); the roof acts as a structural diaphragm, transmitting lateral forces to the racking panels of the load-bearing walls. Connectivity between structural components comprised basic carpentry or simple bolted connections. The existing structure was concluded to be sound. Our intervention was limited to dealing with localised areas of timber decay that had arisen from long-term exposure to water ingress together with adding the bolts that had been overlooked when the building was originally built.
The existing structure can be described as efficient. Like many mid-twentieth century buildings, its capacity to accommodate additional load is limited, even if such additional load is small. Our focus was checking that the weight of the new insulation on the roof would not be problematic. A detailed appraisal of the joist capacity from first principles, underpinned by load capacities identified in contemporary technical literature on similar joists we were able to find, allowed us to show that the additional construction could be accommodated without recourse to strengthening work. This work was a good example of how detailed investigation into an existing structure and reference to primary-source material allows a light touch to be adopted in the care and rehabilitation of existing buildings.