Chris Radley
Senior Associate
Fletcher Priest Architects, London

Chiara Tuffanelli
Senior Architect
Arup, London

Interfacing with a Massive Diagrid Exoskeleton

The Brunel Building fronts the Grand Union Canal, adjacent to London’s Paddington Station and forthcoming Crossrail interchange. A diagrid exoskeleton supports the building over the two subterranean tunnels, while providing column-free floor plates and 20 percent shading to the façade, helping to reduce energy demands while still filtering in sufficient natural light. Creative façade installation and replacement strategies, such as the cantilevered corners, resolved the complexity of the exoskeleton and façade interface. A trackless Building Maintenance Unit (BMU)-suspended cradle was positioned adjacent to the glazing, while installation occurred from the interior.

Structural penetrations through the façade required detailed thermal assessment and condensation risk analysis to devise a solution that would provide both structural and thermal integrity. The main cladding system comprises a thermally-broken aluminum unitized curtain wall, with an insulated strong-back spandrel system spanning the diagrid and fixed at column locations. The double-glazed units are then bottom-supported to the strong-back steel spandrel and restrained to the spandrel above. The insulated strong-back spandrel with a perforated rainscreen hides the slab and spans between structural hard points at stub locations, where an insulated collar shields the thermal break, located at the inner diagrid surface.

The ground floor was designed to present an almost overwhelming sense of scale, while providing a permeable space for the public. The high entrance between the diagrid feet and orange-painted steelwork directs people into the building from alongside the North Wharf Road and the canal which, prior to the building’s opening, was inaccessible. The addition of wide steps and a glazed lift provides outdoor seating along the canal’s bank.

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