Façade Consultant: Arup
Client: Duke Street Property
Architect: Grafton Architects, tp bennet
Façade Contractor: Grants Group, Structura
The Parcels Building was a unique opportunity to promote the retention of an existing building through the principles of sustainability and regenerative and adaptive reuse.
The eight-storey building is located next to the Selfridges & Co. department store on London’s Oxford Street and Duke Street. The intervention was pioneering when the concept was developed in 2018, and focused on reinvigorating an asset which at the time was underperforming in respect to its efficiency and commercial value. This was achieved through a more contemporary and sustainable vision which encompassed the retaining of the existing structural frame and the revitalisation of the architectural concept. The strategy included the design of the new façades, as the main cladding was largely beyond the end of its service life for reuse.
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The result is a modern and efficient integration on Oxford Street, sympathetic to the opposite Grade II listed Selfridges & Co. department store in materiality and proportions. The new façades in handset stone, architectural precast concrete and generous vision glazing meaningfully contribute to the updated architectural concept, while making a significant impact on the overall building’s energy in use and the users’ comfort and wellbeing.
The coordination between the retained concrete structure and the new façade loads was fundamental to confirm feasibility. The use of heavier architectural precast concrete was optimised to make up the lintels only, acting as “beams” that support and restrain the handset stone piers via lightweight steel frames. In this way, self-weight was drastically reduced. The only elements to fix back to the structure at columns’ location were the lintels. Steel “hugging brackets” were designed around the structural columns to guarantee the correct load path, and hence minimise the intervention on the existing structure and avoid additional carbon and cost.
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The improved performance of the new façades was fundamental to reduce the overall energy consumption of the building, allowing greater emissions savings, and enhance acoustics, thermal efficiency and weather tightness. A passive approach was adopted to optimise solar gains and prevent overheating, while welcoming a generous amount of natural daylight in the offices. The architectural massing consisting of the architectural precast concrete and handset stone with deep windowsills and window reveals, combined with the orientation of the building and the application of high-performance solar control coatings in the insulating double-glazed units, helped balance the window-to-wall ratio, while leveraging solar control and maximising daylight ingress. The benefit in comparison with the previous cladding was remarkable with regards to performance-related efficiency and users’ comfort and wellbeing.
A key design challenge to overcome was the presence of deep windowsills with important projections and protruding cornices. These elements had to be carefully detailed to minimise the risk of staining on stone and precast concrete. The strategy consisted of the implementation of design expedients such as adequate falls, specific “noses” with drips incorporated into the design of the projections, and edge drips in all other locations. The design of the “noses” in the precast concrete lintels was researched in relation to both technical feasibility and architectural integration. As a result, the application of surface protection treatments was discarded. Extra cost was avoided, and the cleaning and maintenance regime was optimised to the standard regime used to face the natural weathering.
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The retrofit intervention carried out on The Parcels Building gave an existing asset a new lease of life for present and future generations. The holistic design successfully reduced overall embodied carbon, optimised performance for reduced energy in use, and reinvented an existing building now able to inspire the people and keep them pleasantly engaged. All aspects that were substantiated by the achievement of high sustainability credentials in line with the EPC-A rating and BREEAM Outstanding certification as testament of the hard work and relentless dedication to sustainability of the whole Project Team.
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