Façades that are durable, long lasting and kind to both the environment and building users are crucial if we are to mitigate the effects of climate change. So how are architects, engineers (structural and façade) and manufacturers designing and fabricating façade systems that provide improvements in operational energy without sacrificing embodied energy? What are pros and cons of reuse and circular economy principles in relation to sustainable façade design. And what roles can structural glass and other material innovations play in producing efficient and long-lasting building envelopes? These questions and more were explored in this AT webinar, supported by Kuraray and Powdertech.

The event was chaired by AT Editor Isabel Allen, and the speakers were Damian Rogan, Director of Facade Engineering, Eckersley O’Callaghan; Richard Besant, Sales and Marketing Director at Powdertech (Corby); Julia Torrubia, Senior Environmental Designer at Atelier Ten; Allan Gibson, Global Product/Marketing Segment Manager at Kuraray; and Dijan Malla, Senior Associate at Fletcher Priest Architects.

Damian Rogan kicked off with a discussion about carbon, comfort and circularity, with a particular focus on structural glass. While acknowledging that reducing the percentage of glass is generally ‘the responsible thing to do’ he cited Beijing Library, won in competition with Snøhetta in 2018 and completed last year, as an instance where a structural glass façade proved to be the most appropriate solution. A key priority was bringing high-quality daylight into a huge building with a deep floor plan – the library has a total floor area of 75,000 square metres and contains the world’s largest reading room.

While a steel structure might have seemed the obvious choice for its 20-metre high façade it was deemed too heavy and visually obtrusive. The preferred solution – a façade that is 60 per cent sawtooth, folded, laminated glass, silicon bonded at the edges with solid areas at the bottom – is extremely transparent and 30 per cent lower in embodied carbon, when compared to a comparable steel structure. An overhanging roof provides solar control, while rooflights bring additional daylight deep into the plan.

Allan Gibson explained how using a structural interlayer, such as SentryGlas, can reduce the embodied carbon in glass façades without compromising safety or structural performance. The interlayer allows for larger panels, hence decreasing the amount of framing required, and/or allowing for the use of thinner panes of glass. He used the example of the Montparnasse Tower in Paris (originally built between 1969 and 1973), where the 40,000-square-metre facade has been replaced with Kuraray laminated glass with a structural interlayer. This lightweight solution has reduced the carbon footprint by 15 per cent when compared to a standard PCB interlayer.

Dijan Malla presented a case study on Fletcher Priest’s renovation and extension of Marylebone Place, a 1930s building in central London. The original brick-faced building had been extended in the 1960s with unsympathetic additions, including a redundant car park structure to the rear. Fletcher Priest’s reworking of the project retains 85 per cent of the existing structure and façade, saving 7,515 tC02e of embodied carbon and reducing the duration of the project. Opening windows provide natural cooling and ventilation throughout. Good internal daylighting, external views, and access to outdoor terraces enhance occupants’ health and wellbeing.

While the original brick block has been retained, new south-facing stepped terraces replace the later additions and negotiate the required change in scale, terminating in a timber structure, faced in an orange faience brick. Terraces have cascading plants with timber acoustic screens that also restrict overlooking. A contemporary mews building has replaced the incongruous and redundant service block and car park. Constructed from a lightweight Glulam and CLT structure, it represents a saving of 19tCO2e compared to a more conventional concrete or steel alternative.

Richard Besant outlined the advantages powder-coated aluminium can bring to every stage of the construction journey, emphasising the lower transportation and energy costs of delivering the materials for a lightweight façade. He explained that a lightweight aluminium façade requires less additional support than a traditional heavy façade, is quicker and easier to install, delivers a more uniform result, and can be bespoke to contemporary requirements around issues such as ventilation and insulation. Besant also pointed out that aluminium can be 100 per cent recyclable without any reduction in its original strength, arguing that increasing the use of aluminium not only in the façade, but in the substructure would increase recyclability by reducing the variety of materials used.

Finally, Julia Torrubia outlined Atelier Ten’s approach to synthesising the various factors that inform façade design, explaining how consideration of embodied and operational carbon, aesthetics, acoustics, daylight and views place different – and often contradictory – pressures on design. Extensive glazing is desirable in terms of daylight and views, but not in terms of embodied carbon and energy use. Shading reduces overheating but comes with embodied carbon, and can have a detrimental impact on daylight and wellbeing. Openable windows reduce cooling loads, minimise overheating, and give occupants’ control over their environment, but use more embodied carbon than fixed windows and can let in pollution and noise.

Atelier Ten starts façade schemes by reviewing the form factor (a high façade-to-floor space ratio results in high heat losses, and high energy use, as well as high embodied carbon) before undertaking shading analysis, daylight analysis and finally, parametric testing. This process establishes design parametres, which can then be worked up into an architecturally appropriate façade design.