Changing market priorities saw Morris+Company shift to a unitised facade system for its Featherstone Building, but respect for the ancient context was critical
When Morris+Company designed The Featherstone Building, a multi-tenant workplace near London’s Old Street, it drew direct inspiration from the many Victorian warehouse buildings in the locality.
Through extensive photographic research and drawing studies, the practice sought to define the essence of the type, from the nuances of the composition of base, body and crown to the range of materials and the crafted detailing. The aim was to abstract these elements to come up with a contemporary reinterpretation that was very much of its place. At the same time, the design needed to mediate between the bustling City Road with its tech-industries hinterland, and the adjacent grade I listed Bunhill Fields – resting place of William Blake and many other illustrious figures – which it overlooks to the rear.
The plan had been to build the facade traditionally using hand-laid bricks and precast concrete components on a steel frame system backing wall. However, with the exception of the ground floor, the facade instead ended up being manufactured 2400 miles away in Latvia as a unitised system of brick slips and glass fibre reinforced concrete (GRC), with just under 900 unitised panels craned into place in a carefully marshalled just-in-time installation sequence. This shift in approach reflects changes in the procurement market over the long duration of the project, for developer Derwent London, which began in 2013
Tenants are now starting to populate the 15,938m² building, a redevelopment of two 1960s buildings which increases the floor area by 81%. Rising to 11 storeys on City Road, it steps down in height to 10 and then five storeys in a series of volumes that are staggered in plan as well as height. Its mass is further mitigated by the use of two colours of brick so the scheme reads as four main adjoining buildings rather than one, 80m-long, tapering development. The double-height corner main entrance is recessed to create a sheltering portico.
According to Morris+Company director David Storring, the Featherstone Building is conceived as loose-fit and long life with 3.125m floor to ceiling heights and built-in ‘hard soft spots’ to enable future flexibility for linking floors. The heating and cooling strategy utilises the exposed concrete frame for thermal mass and employs concrete core cooling, trialled previously by the developer at Allford Hall Monaghan Morris’ nearby White Collar Factory. Sensors are incorporated to maximise operational efficiencies and minimise energy use. Supply air is delivered through the floor plenum. Oak detailing in the lofty reception and common areas combine with glimpses of the exposed concrete frame.
The warehouse-inspired facade composition was finalised following what Storring describes as ‘a journey of model-making and craft’ that continued from 2013-18. This included extensive physical studies, from countless card models right through to 1:1 mock-ups. The resulting warehouse reinterpretation meets the architect’s aim of achieving a background character while providing sufficient visual interest through its combination of brick, textured lintels and balustrading.
Brick piers (each four bricks wide) set on a 3m grid provide a regular rhythm. This is interspersed with window bays, each a pair of openable bespoke Schueco aluminium windows divided by a 110mm-wide GRC mullion. In most cases, a single scalloped lintel completes the T-shaped configuration, its 100mm-deep recess creating shadow and interest. There are some variations, including the use of a double scallop on the upper level to define the crown of the building.
A stringcourse clearly delineates floors. Additional variety is created by the placing of Juliet balconies with scalloped balustrading and areas of solid facade, to shield the backs of risers, for example.
Establishing the design was just the start of what turned out to be a long journey to work out how to realise it. Facade consultant Eckersley O’Callaghan (EOC) looked at 12 options ranging from the traditional robustness of hand-laid bricks and precast concrete elements through to DfMA (Design for Manufacture and Assembly), including the use of brick slips. Although such a substantial building offered economies of scale to unlock the potential of off-site construction, and the design team wished for a DfMA approach, in 2016 the market still favoured traditional hand-laid brick construction and precast concrete.
But by the time the main contractor was involved in 2018/19, market priorities were shifting, influenced by shortages of skilled labour and the availability of better quality brick slip and GRC options. Coupled with the restrictions of the tight site and the ambitious programme, this made a unitised approach more viable. Having established that it would provide similar efficiencies in operational carbon, the switch to unitised was made, using brick slips on a GRC backing as part of a lighter weight, unitised curtain wall. This had the added advantage of halving the amount of brick required, and was used for everything except the ground floor, where the brickwork can be touched and observed up-close. Here it was built traditionally. The unitised approach also improved airtightness. A three bay, 1:1 mock-up of the facade was built and included in the tender documentation, with the successful facade contractor – Skonto Plan – required to build a demonstration bay next to the mock-up as part of its tender.
The biggest challenge, according to EOC director Hugh McGilveray, was getting it to look as much like a hand-laid traditional warehouse as possible, while incorporating a manageable jointing strategy, and designing for maintenance and disassembly to ensure longevity.
Both the mullions and lintels were created in precast GRC, with Reckli moulds employed on the latter to create a hammered effect using texture in a nod to patterned tiles. A retarder in the mould helped to avoid the distraction of a glossy finish. The lintels and mullions are created in light and dark shades (Crest BST’s Gibraltar and Weinerberger’s Cinder Grey) according to the hue of the adjacent brickwork of each block. The contrasting shades also reference the variety of materials found in the gravestones at Bunhill Fields, such as black granite and white limestone.
‘We wanted to make a really clear differential between the blocks. There’s a risk in townscape that you can make too subtle a differential,’ says Storring. Aluminium frames, balustrades and any opaque panels were given a metallic lustre with Tiger paint. Care was taken to create 20mm shadow gaps between frames and piers.
After Skonto had constructed the facade units in Latvia, they travelled to site where they were craned into place – the brick piers separately – on pre-set brackets using a small installation team.
Another big design challenge was dismantling and maintenance, with the need to make the GRC stringers and lintels demountable for both maintenance, such as inspecting the slab-edge gasket, and for ease of replacement of individual components if required. It is hoped that this will enable the facade to last beyond its 40 year theoretical service life.
EOC recently revisited the decisions made on the choice of facade construction, carrying out a Whole Life Cycle Assessment on both the built facade and the original hand-laid brick design, with the assumption that the unitised option would need to be refurbished once during the lifespan of the building. While the unitised option was more circular and slightly lower in upfront carbon, the assessment suggests that it has the potential to be slightly more carbon intensive in terms of whole life carbon due to its shorter service life, highlighting the need for careful maintenance and considerate refurbishment in the future. The research also concluded that the construction industry should have more regard for facades and buildings as material banks for future use, and that design for disassembly, adaptability and reuse should be promoted early in the conception of projects.
The Featherstone Building is aiming for BREEAM Outstanding and LEED Platinum ratings.