1 Triton Square is a game-changing example of sustainable building reuse. A whole life carbon strategy has saved more carbon in the building’s design and construction than it will use over the next 20 years of operation.
The new building provides three new floors, twice as much net office area, a BREEAM Outstanding sustainability rating, retained façades and superstructure and no increase to plant space. Five panoramic terraces provide space for events, socialising, meeting, working, exercising and relaxing. 492m2 of green roofs and 536 cycle spaces, along with lockers and showers, encourage active lifestyles and green travel. BREEAM awarded it the Best Commercial Project (Design Stage) in their 2020 awards.
A focus on circular economy principles guided the redevelopment. The team used a ‘marginal gains’ approach to understand what could be retained, reused or replaced, designing, refining and optimising dozens of systems, components and strategies that, together, delivered deeply significant results. Triton Square also exceeds the ambitious carbon reduction targets set by the UK Climate Change Act, which are required to meet the UK’s commitment to the Paris Climate Agreement and is one of the only commercial buildings across the whole of the UK to do so.
Assessing the existing building
Part of a campus development at Regent’s Place, in the West End of London, 1 Triton Square is located within London’s ‘Knowledge Quarter’, a focused centre for academic, cultural, research, scientific and media organisations. Designed in the mid-1990s by Arup Associates for the banking sector, the original building featured trading floors and a vast central atrium. British Land invited Arup to reimagine and adapt the structure for today’s work styles. Lendlease, the original contractor, was also brought back in. Gartner was the façade contractor.
1 Triton Square had achieved the biggest pre-let in the West End for over 20 years. British Land, an all-Arup design team, Lend Lease and the prospective tenant formed Team Triton to develop a vision for its future, guided by British Land’s Brief for Developments which sets targets for exemplary Wellbeing, Community, Futureproofing, and Skills and Opportunities. From the beginning, they were looking to achieve a significant increase in floor area and volume, along with tenant-specific requirements for improved circulation and interactivity throughout the building.
The team recognised several aspects of the building that would work to its advantage. Its rational geometry, which repeated from elevations to individual façade panels, lent itself to further extension. The original structure was built for the high loads demanded by dealing floors and building service systems were designed for high capacity. The façade was a pioneering example of a double-skin system. The building was designed to be disassembled, and as an adaptable asset, the team could more easily apply circular economy principles to facilitate its regeneration. The team took a rigorous risk-based approach to assess whether components could be safely retained, refurbished, or replaced. Where necessary, the team would upgrade elements to align with contemporary performance and safety regulations and standards.
The original layout featured a square plan with corner cores. The approach was essentially one of recalibrating the original design. Regents Place had grown over the intervening years, and newer buildings had established a higher horizon line. The proposal was to add three floors, to build the cores up to reinforce these, setting back the upper storeys to create terraces and sliding up the outer skin by one storey to allow the building to interact with the square at ground level. The corner facing the square was reconfigured to give it better prominence and engagement.
The vast 36m x 36m atrium would be reduced and infilled with a new steel structure to increase the available floor area. Large openings were introduced that vary on each level and allow natural daylight to flood onto the floorplates.
The original facade design solution was a performance-led, integrated mechanical/ façade system, featuring a pioneering double-skin system, a single glazed outer screen and an inner screen of double-glazed ribbon windows with a 1m cavity in between where the mechanical systems ran.
Stair cores would be placed outside the thermal line, with nominal heating for frost protection, to improve airtightness and energy efficiency. The MEP systems were also reviewed to improve efficiency whilst retaining some of the primary principles of the original MEP strategy.
Team Triton and Marginal gains
The success of 1 Triton Square resulted from many years of individual pieces of work by Arup and others around design for a circular economy by reusing buildings, materials or components. Bringing these ideas together into one building demonstrated that a combination of a small number of interventions could achieve significant carbon reductions.
This approach was inspired by ‘marginal gains’ strategy, pioneered in the world of competitive cycling by Dave Brailsford, manager of Team GB and then Team Sky. It works on the principle that even minor improvements can combine to create a significant impact, using data to identify where and how tweaks can be made. Team Triton, as they then modelled themselves, quickly reached a point where they could get from BREEAM Excellent to BREEAM Outstanding for a minimal extra cost. As it turned out, this was roughly 0.3% of capital expenditure, compared to a perceived industry norm of around 5%.
This collegiate approach was an integral part of 1 Triton Square’s success. Team Triton delivered the project through a commitment to partnership and embracing innovative ideas from everyone involved. It is true to say that the circular economy approach couldn’t have worked without it.
Marginal gains were achieved through several strategies. These included high performance unitised facades with retained and refurbished facades where appropriate; extensive energy modelling and MEP systems optimisation; an advanced method for reducing waste generation with 100% construction waste diverted from landfill and innovations by the team to produce extra Environmental Product Declarations. The project also pioneered British Land’s first carbon fibre column wraps rather than adding additional columns to support the new floors. This method saved on installation time, minimised visual impact and, at only 4mm thick, saved around 55% of floor space compared to a traditional approach. For the foundation strengthening, the introduction of mini-piles and a piled raft saved 30% of new piling and £1 million in cost compared with piles and pile caps. The decision to create a pop-up factory in Essex, instead of returning the façade panels to Germany for cleaning, saved 25,000 transport miles and had the added benefit of creating local jobs. Team Triton’s innovative approach achieved an 85% uplift in net floor area without increasing the basement area or the need for additional plant space.
Threading together old and new facades
The existing double-skin façades comprised an outer screen of monolithic glass fixed to 3m wide unitised storey-height frames, hung at the top and restrained at the bottom. The inner screen, a double-glazed ribbon window system, was installed into a strong-back system.
The most significant advantage of this system was its performance. The outer screen helped to modulate the solar gains through the glazing. The inner screen adequately insulated the building, which meant it could meet today’s energy and sustainability targets and achieve the targeted BREEAM Outstanding rating.
The strategy was to dismantle the external screen, assess the design life of its elements, refurbish and reinstall.
The outer screen was moved up one storey to maximise daylight on the ground and first floors and re-engage the ground floor with the square beyond. The entire outer screen was demounted with the lightweight, prefabricated units sent to a pop-up factory 30 miles away in Essex. There, the units were disassembled, cleaned, inspected and returned. End of life components such as gaskets and seals were replaced, and the glass and framing were kept. The glass and carrier frame for the ribbon windows were replaced with new panels for the internal screen.
The team identified 25 façade types, including both primary and sub-types. Using the Unitybased ‘Arup Street’ application, a digital model was prepared to map out the primary cladding systems, identifying the type, the materials and whether it was a new or reused façade. The new facades on the upper floors were designed for future disassembly. The 3m-wide double glazed, thermally broken unitised curtain walling system was dry glazed with external horizontal and vertical cover caps and high-performance solar coating to reduce solar gains. 300mm-deep aluminium fins at 9m centres vertically and 4.05m horizontally created a mega frame. Within this frame, shallower horizontal fins on the south facade and vertical fins on the east/west facades provided shading.
For the entrance glazing, a double-height facade was created using a minimal aluminium stick curtain-walling system. The mullion profile was structurally bonded to low-iron triple or quadruple laminated glass fins, which span the full height of the entrance. Curved glass corner panels completed the facade. The doubleglazed insulating units were toggle fixed to the mullions. The system also includes operable structurally glazed, insulated glass louvres, motorised and connected to the building management system.
A stand-out feature of the original building is the French limestone cladding. With the additional storeys, new areas of cladding were required that, visually, would match.
The team focused on a strategy to blend the old and new stones. With access to the built information for the building, Team Triton returned to the original quarry in Val de Nod in France, taking one of the original and now cleaned panels with them. They agreed on an acceptable colour range and Arup developed a programme for the stone placement to ensure that there was no apparent distinction between the new and existing stone panels. The original stone cladding was fixed back to an existing precast panel system. A lightweight system was designed with the new cladding fixed back to a unitised curtain wall to avoid reinforcing the structure significantly. The team saved 3,300 m2 of limestone by retaining materials, equating to a reduction of 1,060 tonnes of embodied carbon. Granite panels on the ground floor were also kept.
At the southeast corner, the reconfigured core introduced a new feature entrance to bring visitors into the double-height atrium. The unitised cladding system incorporated external horizontal and vertical shading elements of an aluminium structure with GRC cladding panels and with the potential to be fully disassembled, thereby ensuring future opportunities for upgrade and regeneration. The units were visually tested against the mock-up, off-site tested at Gartner, then shipped to the site and installed as a unitised module.
For the reduced atrium rooflight, the team undertook extensive daylight studies and glare analysis to determine the impact on the office spaces. A self-stabilising structure was used that would not require support from the primary structure, thus saving on concrete. 18m portal frames were developed with deep, tapered steel sections to minimise deflections without recourse to increased material. The largest available glazing modules were used to bring maximum light into the atrium and contributed to the efficient installation of the frames, which were brought in as large single units, thereby minimising on-site lifts.
The design was subjected to extensive weather performance and impact testing, including construction sequencing and disassembly methodologies. We reviewed British Land’s policy on double laminated glass build-ups concerning flat glass in rooflights. We proposed changing the outer pane material from laminated to monolithic, which reduced the embodied carbon of the glazing by over 20%. This transition was supported by a risk assessment, which detailed the failure modes and the resilience of the design, and an impact testing regime. The team also used proprietary systems and standard components in the design to minimise cost and reduce lead times.
Key to the project was the wealth of information available to the team, from design stages to construction. As-built drawings were fundamental to understanding the original system, its performance, and how to successfully interface between old and new elements. Early conversations with the original façade contractor, Scheldebouw, and review of the existing building’s works drawings and specifications offered an insight into the existing façade and the possibilities for retaining or reusing without requiring intrusive surveys.
The result has been a resounding success. Removal, refurbishment and reinstallation of over 3,000 sqm of façade and other façade interventions contributed to almost a quarter of the whole-life carbon reduction. Reuse of the aluminium-glass units gave a 66% cost reduction compared with similar replacement units, and the refurbished outer screen is designed to last another 35 years.
1Triton Square performs exceptionally well compared to the existing building and the latest building standards and benchmarks. The building received nine energy credits, exceeding the eight needed for its BREEAM rating. In total, it has produced 48% less carbon than British Land’s typical London new-build office model. Overall, the scheme’s carbon footprint per unit area is 136kgCO2e/m2, and it achieved a SCORS A rating. It was also delivered 30% faster than a new build with 6,000 fewer lorry journeys.
It is also important to note that 1 Triton Square exemplifies the ‘golden thread’ of information. Robust design and construction documentation, from the original building to the recent additions, is enhanced by new elements that are designed to be disassembled. It means that continued regeneration will be possible, making the building as adaptable in the future as it has proved to be in the present.
This article was originally published in IGS Magazine’s Autumn 2021 Issue – Glass Retrospective: Read the full Magazine here for more thought-leadership from those spearheading the industry
Nick is a Director within Arup’s architecture group with a focus on commercial property and workplace sectors. He has led teams on many successful major projects over the last two decades including office, mixed use, and residential developments, as well as green field and urban regeneration masterplans. Nick has a focus on expanding the opportunities for the group to undertake sustainable commercial property projects, with a priority on exploring opportunities for low carbon refurbishment and retrofit projects of major assets.
Matteo is a Senior Engineer in Arup’s London Façade team. He has worked on a wide mix of new-build and retrofit projects ranging from residential and commercial developments to high rise, cultural and mixed-use projects in Africa, Middle East, India, Australia, UK. Matteo integrates complex environmental analysis and simulation, focusing on building physics, CAD advance modelling, and BIM. His specialist knowledge includes optimisation for daylight and visual/thermal comfort, passive design, fabric performance and energy efficient design.
Cover image: © Simon Kennedy