Circulation Strategies

This article was originally published in Blue 02: Systems and Structure in 2010. You can see the article in its original format, and other articles, online.

The St Botolph Building in London, a landmark development by Minerva plc, is Grimshaw’s largest commercial office scheme to date. Providing over 52,000 sq m (560,000 sq ft) of lettable space, it is located on an ‘island’ site near Aldgate, within the City, London’s oldest and most prestigious commercial business district. The building has been designed for multiple tenancies, with nearly half the space already let to two occupiers: insurance brokers Lockton and law firm Clyde and Co.

Grimshaw began designing a building for the site in 1997 and the current scheme, now in the final stages of construction, was developed from a planning consent gained in 1999. In the spring of 2006, Minerva asked Grimshaw to update the 1999 plans and ensure that construction could begin within 12 months.

With nearly 10 years of change in the London office market since the project began, we took the opportunity to review the internal planning. The design strategy for the building proved to be robust and remains unchanged; however internally the detailed execution incorporates major developments.

To provide maximum occupational flexibility, Grimshaw’s design places the circulation and service cores at the outer edges of the floor plate. This balanced layout of four perimeter cores creates space suitable for the broadest possible range of occupiers including small-scale dealer operations.

With the two lowest office levels identified as potential dealing floors, the passenger lifts (elevators) could not be located centrally as this would interrupt the open plan space required for trading. In the 1999 scheme, the lifts were grouped in one enlarged perimeter core whilst two atria brought daylight into the centre of the building but stopped above the dealer floors.

Although the building has only 13 office floors, the floor plates are larger than commonly found in central London commercial buildings; up to 3,900 sq m (42,000 sq ft) of lettable area each. To adequately service these floors, lift capacity analysis suggested a system that one might expect in a much higher building; 14 lifts split into a group of eight serving the lower floors and a further group of six serving the upper floors.

These two lift groups dominated one end of the floor plate, even if one group was placed in a central atrium and did not provide ideal access to any floors that would potentially need to be divided into smaller sub-tenancies. Working closely with specialist consultants Preston Dynamics, the vertical circulation strategy became subject to intense scrutiny.

The design team also started to explore more innovative lifting technology. Double deck lifts (two passenger cabins fixed one above the other and moving together) would have reduced the number of lift shafts and freed up valuable floor space, but they also come with some significant disadvantages. For example, users experience “false stops” as passengers in the linked cabin get in or out. Also, the lift cars are much heavier, requiring bigger motors and heavy-duty running gear. In the St Botolph Building we also had different floor to floor heights to cope with. This would have required the double deck lift cars to be ‘articulated’ with the two cabins moving closer together or further apart. Again, this meant more weight and more money, along with the higher risk of breakdown. Ultimately, the high cost and poorer service killed this option.

In the interim, between gaining planning permission in 1999 and the project re-commencement in 2006, lift technology had also improved markedly. To gain maximum efficiency in large lift installations, manufacturers had developed computerised systems that respond to user demand. Typically referred to now as “Destination Selection Control” (DSC), users first select a destination floor and are then directed to use a specific lift car instead of taking the first lift moving in the appropriate direction and then choosing their destination floor when inside the lift car.

This technology allows all journeys within the lift group to be co-ordinated by allocating the most appropriate car for each user’s journey. Ten years ago when the St Botolph Building was first designed, this was new technology, and treated with some scepticism by developers and their tenants. By 2006, assisted by widespread use in new towers across the globe, DSC was readily accepted by London tenants and the letting agents whose advice oils the office development machine. This acceptance was a crucial tipping point for real innovation in lift technology.

As a next step in the evolution of lifts, the idea of running two lift cars independently in the one lift shaft was explored. Once DSC was accepted, it became a real possibility. The DSC system allows the movement of two lift cars to be safely and efficiently co-ordinated. This emerging technology provided a better answer for the St Botolph Building, and the opportunity to do something innovative. In the autumn of 2006, the project team began to investigate dual lifts in detail.

The substantial benefits of the system were immediately obvious. Instead of 14 shafts we needed only 8, with smaller lift cars (21 person instead 26 or 24 person). Not only did this increase the lettable office area, it allowed all the passenger lifts to be located within a single group housed in a dramatic 13-storey central atrium. This in turn allowed the combined lift core and atrium to continue down through one end of the dealer floors, linking directly to the reception space, whilst above the atrium could take a stepped form to become three times larger at its highest point. Combined with the perimeter core strategy, the addition of bridges in the atrium could provide direct access to four separate sub-tenancies on each floor, with no additional lobbies or corridors in the office space.

The lift car structures, running gear and motors are the same as conventional lifts, although the lift motor room is rather more congested. Maintenance costs were predicted to be 12% lower than conventional lifts as there would be fewer shafts and landing doors. The 2.2% premium on capital cost was more than offset by the 16,000 sq ft increase in lettable area.

This combination of space planning, technical, and architectural design advantages provided a compelling design case for this lifting strategy but there were other issues to be resolved.

Only one company, Thyssen Krupp, has developed the knowledge and equipment to manufacture what they call the “TWIN” lift system. Thyssen’s TWIN system employs a four-level safety concept ensuring that the cars maintain a minimum clear distance from each other during operation. This includes two entirely separate computer location systems for the lift cars, either of which can shut the system down.

In 2006, Thyssen had a working system that had been installed on a small scale within a few buildings in Germany, including one example in their own head office, and a large order for a scheme in Moscow. The TWIN system was not certified for use in the UK, although an application had been made and approval was anticipated by the end of 2006.

If we were to go ahead, this would be TWIN’s first use in a UK office development, indeed their first use in new build in the UK and the biggest TWIN installation ever commissioned. To add to the ambition, we wanted to locate the lifts in an atrium so they would also be TWIN scenic lift shafts.

The office development world (or perhaps more precisely some tenants and their advisors) can be quite conservative and wary of anything that might be judged risky or ‘different’. With the advantages of TWIN lifts established, Minerva and the design team began a careful evaluation process. This included discussion with letting agents, technical reviews, inspection of existing installations and a host of detailed due diligence work. At the conclusion of this process, the biggest concern was the risk inherent in a commitment to one supplier at an early stage in the design and procurement process. If the full design advantages of TWIN lifts were to be taken, the design could not easily be changed back at a later stage.

If we were to go ahead, this would be TWIN’s first use in a UK office development, indeed their first use in new build in the UK and the biggest TWIN installation ever commissioned.

In January 2007 Minerva committed to use TWIN lifts for the St Botolph Building. Thyssen Krupp was appointed to help the design team prepare contract information, and our detailed design work began.

Adoption of the TWIN lift strategy had a huge impact on the building design, especially at the building entrance. To work efficiently, TWIN lifts need two loading levels at the ground floor, so that both cars can be fully utilised for peak traffic flows. This immediately led to a concern about one level, and hence some users, being seen as ‘second class’, especially if this involved moving down from the entrance doors in order to go up in the building.

To serve well over 5,000 occupants, the reception design that Grimshaw developed occupies half of the building at ground level. Much of this space is carved away in the centre of the entrance hall where the lifts are located, so that the ground floor becomes a large 6m high balcony surrounding a 10m high central arena that opens into the stepped atrium above.

The upper lift cars are accessed from a glass bridge mezzanine within reception whilst the lower lift lobby is part of the generous lower ground level which benefits from the building’s social facilities that will be grouped here when fit-out is completed. The client’s ambition in this space is to create the same sense of service and comfort provided in Virgin Airline’s upper-class lounges. Both levels are accessed by paired escalators, running alongside bespoke aluminium 'blade' clad walls that guide users through the space.

The reception hall provides the first view of the lift core that is the centrepiece of the building’s interior design. This 16-storey steel structure places a kinetic sculpture in the central atrium, with movement of the 16 lift cars and their counterweights visible throughout the heart of the building. We deliberately set out to celebrate and display the engineering of the structure and the systems: all of the steelwork and lift gear is exposed against the calmer background of the surrounding atrium wall cladding. The walls, floors and soffits of the lift lobbies are all glass and where bridges to the office floors are required, they are supported off the lift core's steelwork with a “drawbridge” design that clearly shows how the loads are taken back into the main structure.

We felt that glazed lift cars might be a step too far for user comfort and with the lively activity of people and carefully crafted engineering components surrounding them, it was decided that the lift car interiors should provide a moment of calm. The interiors maximise contrast with their immediate surroundings and continue the white marble floor of the reception area allied to other simple high-quality finishes, including stainless steel and glossy white walls and ceilings.

During our visits to the Thyssen Krupp factory we had been intrigued by their colour coding of all the TWIN lift gear. This is used for safety, helping maintenance staff to identify which set of equipment they are working on although in the only scenic installation that we had seen, the colour coding had been minimised in the public zones.

Continuing our aim of exploiting and celebrating the engineering design we spotted the potential for colour coding to provide another layer of interest. With blue as the building’s main exterior colour, led by the blue glass spandrel panel in the external walls, we selected the remaining two primary colours for the passenger lift system.

For these key elements we sought more subtlety than simple boxes of colour. The outer three walls facing the office floors are silver aluminium planes that extend beyond the roof car and floor to engage with and shield the lift slings and running gear. Cool and calm, smooth and business-like, they continue the theme of curved corners and overlapping planes used in the blue glass exterior walls of the building. However, like a bright lining to a sober business suit, the aluminium skin shields a burst of colour. The lid, underside and doors of the lifts are bright red (upper cars) or acid yellow (lower cars) and can clearly be seen from the glazed lift lobby as the lift arrives and even glimpsed from the office space through the lobby’s glass walls. The exceptionally tall thin counterweights then use a reversed layout with coloured frames surrounding a silver skin.

Attention to detail in engineering and construction is a fundamental part of Grimshaw’s design philosophy. The St Botolph Building is at the upper end of the office building spectrum in the UK, seeking high rents even in the depths of recession. Therefore, everything in this project, to continue the tailoring metaphor, is bespoke. Indicator panels in the lift cars, lift guide rail support brackets and lift shaft signage all use themes that are developed throughout the building's components to provide a consistent and common design language.

Within the TWIN lift system, implementing the client’s and architect’s design ambition has been hugely helped by Thyssen Krupp’s engineering resources and heritage. Unusually for a lift company, they manufacture almost all of their own components, from electronic circuit boards to motor pulleys. When we needed a stainless steel skirting in the lift cars that was folded and curved without welding, the skills to make it were found in Thyssen’s team that make the casings for escalators.

​Attention to detail in engineering and construction is a fundamental part of Grimshaw’s design philosophy.

The obsession with detail and quality has extended to the smallest parts, including the LCD touch screens where users interact with the DSC system. User expectations for electronic systems have been hugely raised over recent years by well -designed consumer products like the iPhone and it is easy for components in buildings to look very clunky and dated in comparison. Here Grimshaw saw an opportunity to develop and improve the standard product. With no new operating components, but intelligent reorganisation, packaging and graphics, we undertook significant product development. This included turning the LCD screen through 90 degrees, a new stainless steel housing, bespoke graphics by Grimshaw and concealed swipe card readers.

Writing in May 2010, this ambitious scheme is about to be realised. The final stages of production are underway, installation on site is nearly complete and commissioning has begun for the first tenants to take occupation in June. The project team has risen to the challenges and our client has been rewarded for their brave decision with a unique building that has wowed visitors already. By September, all works will be complete and the St Botolph Building will host a party to celebrate 30 years since the Grimshaw practice was founded.