FAADE CASE STUDY | THE BLACK AND WHITE BUILDING REACHING NEW HEIGHTS A six-storey timber faade at the Black and White office building in London helped slash embodied carbon and won its engineer a SFE Faade 2023 Design and Engineering Award. Andy Pearson finds out how the winning design was engineered while alleviating safety risks EMBODIED CARBON The fully engineered timber superstructure makes a powerful sustainability statement, with claims that it contains one-third less embodied carbon than a comparable six-storey structure. Only the basement box and integral ground-floor slab are constructed in concrete. The buildings embodied carbon is calculated to be 410kgCO2em2 (modules A1-A5, excluding sequestration), compared with that of a conventional building of around 670kgCO2em-2. Impressively, the timber structure is bolted together to enable it to be dismantled easily and reused at the end of its life. If its timber is reused, then the sequestered carbon for as long as it is in (re)use lowers the buildings embodied carbon figure still further, to just 180kgCO2em2, below the LETI 2030 target for office buildings For the faade alone, the use of an aluminium/timber hybrid was calculated as having 40% less embodied carbon than the equivalent aluminium system if sequestered carbon is included. T he Office Groups brief for the Black and White Building, a six-storey commercial office development in Londons Shoreditch, was for it to be an exemplar of timber construction. It does not disappoint. Designed by Waugh Thistleton Architects working with structural and faade engineer Eckersley OCallaghan (EOC), the 17.8m-high building features a hybrid beech laminated veneer lumber structural frame, with a core, the floorslabs and staircases all built entirely from cross-laminated timber (CLT). More impressive still is the faade. Designed by ECO, this is also constructed from timber. It features floor-to-ceiling glazing supported by a glulam composite timber/aluminium curtain wall, complete with external timber louvres to provide solar shading. The faades size and innovative use of timber makes it unique in the London office market, an achievement recognised by the judges of this years Faade 2023 Design and Engineering Awards, run the by Society of Faade Engineering (SFE), at which the scheme won the UK Innovation category. Despite initially considering an aluminium faade, in line with typical office buildings in London, we carried out a comparative analysis of embodied carbon and faade-profile depths structurally required to achieve the spans for both timber and aluminium options, says Ben Buckley, senior engineer at Eckersley OCallaghan. Ultimately, timber proved to have significantly lower embodied carbon content than aluminium, while maintaining a comparable profile depth, which maintained the net internal floor areas. One of the biggest challenges in attaching a timber faade to a timber building is the need to accommodate movement from the timber swelling and shrinking in response to changes in moisture. With the superstructure constructed from timber, it is lighter, and prone to greater movement from wind loads and occupancy, than if it had been built with a concrete frame. Fortunately, EOC was also the projects structural engineer, so faade engineers were able to work with their structural engineering The project demonstrated impressive architecture and innovative design while ensuring sustainability was at the centre of every decision colleagues to predict structural movement during construction and when occupied, to ensure these could be accommodated. Early coordination enabled stringent deflection criteria to be specified and designed to minimise the risk of design changes once contractors were appointed, explains Buckley. The curtain wall spans CLT floor slab to CLT floor slab, with differential movement accommodated through the connecting brackets. To accommodate the larger, longterm deflections of the timber structure compared with a concrete structure, we also designed a thicker horizontal transom to accommodate the movements, says Buckley. 22 December 2023 www.cibsejournal.com CIBSE Dec 23 pp22-23 Facade of the year.indd 22 04/12/2023 12:03