67–74 Saffron Hill is a substantial six-storey (including Lower Ground Floor) 1960s commercial building, originally constructed with a reinforced concrete frame and lateral stability provided by reinforced concrete cores and shear walls. The project involved a major vertical extension—adding two wrap-around storeys to increase the building’s height along the west elevation—and a modernisation of the front façade with new large-format glazing panels. As part of a comprehensive upgrade, the building’s heating and cooling systems were also replaced, including the installation of a new rooftop substation and plant equipment.
A key challenge was the structural integration of the two new floors with the existing 1960s frame, particularly given that the building remained fully occupied and operational throughout the works. The increase in vertical loading from the additional storeys exceeded the typically accepted 10% increase on existing columns and foundations. However, by sourcing a full set of original archive drawings—including reinforcement details, pile layouts, allowable loads, and ground beam designs—we were able to undertake a thorough structural assessment. This enabled a carefully considered design response that avoided the need for major strengthening works or disruptive foundation interventions.
The new floors were constructed using lightweight steel framing with composite metal deck slabs to minimise additional loads. Steel columns were strategically positioned to align directly over the existing reinforced concrete columns below, avoiding the need for deep and complex transfer structures. Stability for the extended structure continued to be provided by the existing reinforced concrete core.
The rooftop substation and plant areas required new structural framing to support mechanical loads while maintaining coordination with the lightweight roof construction. All works were planned and executed with meticulous coordination to ensure minimal disruption to building occupants and ongoing operations.
