In the heart of central London, a former mid-20th century postal sorting office is rapidly being transformed into contemporary, steel and glass premium office and leisure space. Retaining the historical character of the building, while making the most of the space, is no mean feat.
Laing O’Rourke’s Payal Tripathi, a graduate engineer working on the construction of the building’s frame, explains.
“The main engineering challenge comes from the requirement to keep a proportion of the original building. “Part of this area once housed sorting office machinery – think huge equipment hanging from above, requiring a massive amount of space. This impressive 5.5-meter-high ceiling is easily double what’s normally offered in central London, so will be hugely appealing.”
As a point of interest historically, the basement houses the original sorting office railway. Although this ceased to operate in 2003, the structure is historically significant. Surveyors must regularly check the space so a safe access point to the area has also been included.
Concrete meets steel
Typical of the era, the existing structure is concrete. However, the new structure incorporates 7,000 tonnes of steel.
“As well as providing the desired aesthetic, the use of steelwork for the main building was driven by weight constraints from the retained substructure and limitations in slab thickness driven by existing geometry. Aligned with our DfMA 70:60:30 ways of working, using metal decking means there are less temporary works, onsite labour and materials. It’s noticeable in the speed of construction – we are already making our way out of the retained structure past the third level, so people can now see the new building taking shape.
Where the geometry and load capacities permitted, we have utilised some of our standard concrete manufacturing products, including precast concrete columns for the residential units and north east core. This has given an intelligent balance between steelwork and concrete.”
So where’s the challenge?
“The technical challenge – and what I found really interesting – is marrying two types of structure, integrating two different trades in the concrete and steel. Creating the supporting connections between the two isn’t easy.
“We’re working from drawings that are around 50 years old and a lot has changed in that time. Plus we’re coming across elements that just aren’t on the original drawings. We’ve been using a Ferroscan to check reinforcement as we go, getting ahead of any surprises. But it’s still meant that areas of the design had to be altered in situ, and loading has had to be reassessed as we progressed.”
Payal says that a digital engineering approach is important, with the team creating a digital model of the old and new structures and adding in any new details they come across. But it isn’t all about technology.
“One of the most important elements is communication and promoting understanding between subcontractors. We use simple technology such as WhatsApp to keep in touch.”
“Linking the old and the new has been really interesting and with the bespoke cladding currently being installed, the structure is now substantially complete and the building has taken shape. The facade design involves prefabricated unitised panels up to 4.8m in size, finished in darkened stainless steel and anodized aluminium, made in Germany with final assembly on site ahead of installation – which provides its own challenges due to the confined site. In the coming months we’ll concentrate on completing the installation of the cladding while internal core, residential and Category A fitout progress internally, ready for practical completion at the end of the year.”