The transformation of the former BT Headquarters, an outdated 1980’s office, into a sustainable, mixed-use building and a new destination on London’s Culture Mile.

The transformation of an outdated 1980’s office into a sustainable, mixed-use building and a new destination on London’s ‘Culture Mile’. Through extension, refurbishment and modernisation, flexible office floorplates are formed, with improved environmental performance, natural ventilation and daylighting; More than 1,330 cycle spaces and associated facilities are provided to encourage sustainable transport; extensive planting and a large public roof terrace will improve biodiversity and make a significant contribution to the greening of this corner of the City.

Creating a sustainable building is a relay race, with each part of the team passing the baton on to the next consultant.

A previous scheme for this site included demolition and new build. But the original building was extremely well-made and we approached the project with the assumption that we could transform what was already there - saving a huge amount of carbon, construction time and waste.

Each project is unique and requires a deep understanding of the original building, but there are common threads. One important element is that concrete codes were very generous for buildings of this period. Without the benefit of computational design, the structural engineers built in more redundancy than they needed. Plus, concrete hardens over time, so the structure of the building is stronger now than when designed. This meant that we could add additional load to the existing frame – allowing for some extension.

A really important element of this project is the façade. From early on we were convinced that we could use the existing building as a ‘quarry’, removing the original Portland stone and granite and reusing it as part of new, high-performance façade.

Of course, it might have been simpler and cheaper to specify new stone. But we felt it was important to reuse what was there. This approach was part of the planning permission, which made it easier to get buy-in from other contractors.

Collaboration and conversation were an incredibly important part of the process. Grants, the stone consultant, really bought into the idea of reusing the stone. Their expertise and craftmanship have been key to removing the original façade with minimum wastage.

We had many discussions about the best way to use the reclaimed masonry. It’s been set into pre-fabricated panels, which can be demounted and refurbished – although the stone can’t be taken off as a single element again. There is a complex set of factors to consider and decisions have to balance carbon, cost, and construction processes. Using prefabricated panels reduces construction time on site and the amount of time that the building has to be fully scaffolded.

Ultimately, a low-carbon development is the cumulative effect of many decisions, and not the result of one grand gesture. We’re learning on every project and feeding that knowledge back into the design process.