With its latest addition to its Regent’s Place campus, British Land has again demonstrated its interest in delivering retrofit projects. But, given the age of the building, how necessary was this scheme? asks Seb Laan Lomas. Photography Simon Kennedy
21 October 2021 By Seb Laan Lomas
Arup’s re-imagining of 1 Triton Square, the 47,195m2 commercial development on Euston Road that the multidisciplinary practice designed in the 1990s and which it has recently reworked for British Land, employed four classic retrofit tips. First, original records were retrieved to inform decisions about latent structural capacity. Secondly, the original designers were reappointed. Thirdly, Arup’s architectural team came under the Arup umbrella, improving dialogue between disciplines. And lastly, the design has significantly increased the building’s net internal area, boosting the project’s viability and maximising use of the retained structure.
Arup’s architectural interventions are discreet (in part led by planning negotiations), including the subtle substitution of the single-glazed wrap with accentuated deep-framed glazing in some areas. The original characterful ‘punched’ main entrance that greeted visitors from Warren Street station has been filled in to contribute to the increased floor area, and a new clear route up to the elevated entrance floor created. While dislocating the main entrance from the ground floor is often seen as a ‘no-no’ with respect to activity and engagement, it has enabled the provision of generous affordable workspaces facing the residential streets to the north, an independent gym, retail units and a secure cycle store directly at street level.
Located in British Land’s fortress-like Regent’s Place campus, the dominant corner stair towers have been left largely unaltered, with their vertical extension identifiable as glazed lanterns. Users of the WELL-enabled building have access to numerous terraces, but the rooftop offering is limited due to an increased plant requirement. Those who reach the roof, however, will discover rich wildflower planting between the new air-handling units.
The project preceded the recent upsurge in addressing embodied carbon emissions. The mantra goes that the greenest building is the one that is already built, but the devil is in the detail and the best whole-life carbon solution is not always obvious. Decisions to retrofit or to redevelop should therefore be informed by undertaking a whole life cycle assessment to illustrate emission profiles for both scenarios, balancing operation and embodied emissions to achieve the lowest-impact solution. In this instance, the decision to not demolish took into account protected views, a shared basement that limited depth, affordable housing requirements, and the fact that retention of a building can save time and carbon emissions. The scheme uses a combination of new superstructure and piled raft foundations alongside a retained, strengthened structure – the latter using 4mm carbon fibre-reinforced polymer to increase the axial load capacity of concrete columns by 40 per cent – a design feature which I hope is left on show.
From planning onwards, the project team, led by Arup’s in-house Life Cycle Assessment (LCA) team, benchmarked embodied carbon emissions against current best practice for new developments and data from the Real Estate Environmental Benchmark (REEB). The project has achieved BREEAM Outstanding (with a 92 per cent rating) but, as Arup project lead Nick Jackson notes, BREEAM currently does not go far enough to align credits with delivering lower embodied carbon outcomes. Where Environmental Product Declarations (EPDs) for products they wished to use didn’t exist, they aided a supplier in creating them.
The project team managed to reinstall 3,500m2 of reconditioned and re-warranted glazed façades
Arup believes the key lesson learned from the LCA process was that overall optimisation is achieved through a spectrum of interventions. That said, 45 per cent of the project’s whole-life carbon reductions (compared with a complete redevelopment) are from retained structural elements. The team states that its collective strategies have mitigated 57,000 tonnes of carbon emissions, which approximately equates to ‘not building’ a development to the RIBA’s unsustainable ‘business as usual’ level. It is important also to consider the holistic impacts and benefits of a development, and in this instance that should include Longford House, the adjacent development delivered simultaneously to provide a portion of the affordable housing requirement. The 22 new concrete-framed homes might be contributing a further 3,000 tonnes of embodied carbon emissions but, with British Land’s current support of unlocking structural timber insurance, one would anticipate a development like this designed again today would include lower-impact solutions with higher-sequestering materials.
Back at 1 Triton Square, most of the existing double-glazed units were still performing but, at 20 years old, their future performance could not be guaranteed. Helped by their understanding of the existing systems, the project team managed to re-install 3,500m2 of reconditioned and re-warranted glazed façades, which look as good as new. Instead of shipping the façades back to the original supplier in The Netherlands, a temporary workshop was established 30 miles from site, where the façade contractor’s UK team carried out reconditioning work. Jackson comments that, while re-using the original team ‘makes it contractually easier’, the same should be thought of as being achievable on other similar projects and must be pursued for our move towards circular designing and living.
In view of Covid, the talk is of increased ventilation rates, and a building with good airtightness could allow higher servicing provision more efficiently than a space combating leaky building elements. 1 Triton Square had two airtightness design targets – of about 3 m3/m2.hr and 5 m3/m2.hr for new fabric and retained fabric respectively, with a weighted average of about 4 m3/m2.hr. This is below the woeful Future Building Standard target of 5 m3/m2.hr, yet some way off the EnerPHit target of 1 ACH (air-change per hour).
Airtightness is still a challenge that needs improvement by learning the lessons from those who are hitting the targets
Part of the airtightness strategy was to double up around the stair towers, with a new airtightness line following the relocated thermal line, leaving the stairs as unconditioned spaces and improving the form factor of the building. On-site testing demonstrated an airtightness of just over 6 m3/m2.hr. The increased permeability was put down to the challenges relating to the retained fabric and the complexities of sequencing testing and improvement. This shows that airtightness is still an industry challenge that needs improvement by learning the lessons from those who are hitting the targets.
Despite this degree of air permeability, 1 Triton Square’s quoted base building energy use is 39 kWh/m2, which is just shy of the UK Green Building Council’s Paris-proof 2035 targets and would fully justify the RetroFirst approach. However, this figure is from the as-built Building Regulation UK Part L (BRUKL) report to inform the Energy Performance Certificate – a certificate that has an awful correlation with actual building performance. A CIBSE TM54 assessment, an improved method of calculation, was also done for the scheme and it paints a very different picture, showing a base building energy use of 162 kWh/m2, differing from the lower figure by over 400 per cent and higher than the RIBA’s unsustainable ‘business as usual’ figure.
Kate Fletcher, Arup’s public health skills leader, explains how a TM54 assessment more accurately demonstrates the energy use for a single scenario based on assumptions such as actual operational hours, but not necessarily representing the most efficient use of the building. For an industry learning to use whole-life carbon assessments to inform whether to retrofit or redevelop, and how to deliver net zero solutions, this predicted performance discrepancy is seriously problematic, at best.
Fresh air will be provided once again via displacement ventilation and insulated external air ducts, distributing air from the cores to the deep-plan floorplate. Despite assurances that their external location and penetrations of the envelope don’t hinder the energy efficiency, it would be interesting to point a thermographic camera at these features when the building is up and running.
The single-glazed layer to the double-skin façade has been refurbished and reinstated, though, disappointingly, there is no data quantifying any performance or qualitative benefits of this atypical feature.
The expansive floorplates wrap around a reduced, yet generous, 17m-wide atrium that draws one’s eyes skywards. But its stack effect does not intentionally contribute towards the building’s 100 per cent mechanical ventilation strategy. Designed in 2016, the modernised servicing predates the predominance of all-electric systems, using gas boilers for both hot air and water, which may notably increase the operational carbon emissions compared with a system benefiting from the decarbonised national grid. There was insufficient space for air-source heat pump condensers, but the building has been designed with connections to support a district heat and energy network in the future.
British Land concedes that this development, which aimed to reduce carbon emissions by at least 44 per cent against 1990 levels, is only part of a long journey, with a graph showing that improvements will still be required within a couple of years to keep to its decarbonisation pathway.
British Land has demonstrated a strong interest in understanding the energy requirements of its portfolio and the building’s meters will feed into their energy monitoring system. As the performance of base buildings improves, the relative impact of the end users increases, and I imagine British Land will have negotiated this within the terms of the lease with the new tenants, a multinational media company which has itself committed to reporting science-based targets. Fletcher agrees that when delivering a shell-and-core building, the responsibility should be to push the base building performance as far as possible to allow for future unknowns.
At 1 Triton Square, Arup has demonstrated its technical ability to deliver a subtle, light-touch evolution of a building experiencing a mid-life crisis in its twenties. And it left its ego at the front door (having redesigned it) to upgrade a building with decades left in its bones. This was done without re-inventing its aesthetics, and time will tell whether the highly glazed façade delivers optimised energy performance.
In many instances, the decision for retrofit over redevelopment requires a progressive collective commitment from an entire team to deliver not what they have done before, but rather to ask what they can do better this time. British Land has successively demonstrated its interest in delivering retrofit projects, both at 100 Liverpool Street and at 1 Triton Square. But, given the building was only 18 years old, it begs the question – how necessary was the project?
1 Triton Square also raises a worrying question about whole-life carbon emissions, and whether the figures we calculate and submit to the RIBA 2030 Climate Challenge could be significantly underrepresenting the true damage that buildings wreak on the environment. Arup calculated the up-front carbon emissions (A1-A5) of the works at 465 kg CO 2 /m2, which is 60 per cent of the RIBA’s 2030 embodied carbon target for a building’s entire lifetime. We are meant to calculate whole-life carbon figures across a 60-year life (putting aside that it is important that most of our buildings outlive this), but how many of us include ‘refurbishments’ like these happening after 23 years? If we are to play our part in stemming the rising parts-per-millions of CO 2 , halting the glacial melt, and abating the wildfires – we must individually and collectively be judicious in how, and how often, we reimagine our buildings. Seb Laan Lomas is an architect at Architype, an ACAN co-ordinator, and was previously head of sustainability at Hopkins Architects
Sustainability actions taken on 1 Triton Square have saved an estimated 40,000 tonnes of CO2 over a 20-year lease, compared with a typical new-build office benchmark – a 55 per cent reduction. This saving is enough to heat and power about 9,900 average UK houses for a year. The scheme has also saved 40,000 tonnes of CO2 compared with a British Land office benchmark over 20-years, a 48 per cent reduction. The reductions achieved are better than those required by the UK Nationally Determined Contribution to the Paris Climate Agreement.
We re-used as much of the existing structure and fabric as possible – 3,300m2 of limestone, 33,400 tonnes of concrete and 1,843 tonnes of steel. This accounts for 45 per cent of the total carbon saving. The new building will provide three extra floors and twice as much net office area as the existing building, all while retaining façades and superstructure and without increasing plant space.
We chipped away at every aspect of the building using Arup’s collective expertise to save carbon, cut waste and deliver the best working environment. Interventions included:
• Pioneering one of the UK’s first large-scale circular economy façades, we removed 3500m2 of panels, which were transported to a pop-up facility less than 30 miles away for refurbishment. • Low-energy lighting, heat recovery systems, upcycling of redundant plant. • Carbon fibre column strengthening allowed up to a 40 per cent increase in axial load capacity, with no impact on area. • A 30 per cent reduction in piling was achieved using piled rafts instead of piles and pile caps. • Stair cores positioned outside the building’s thermal line. • We conducted lifecycle carbon analysis on a number of different products and materials in-house. • 59 per cent cement replacement with 41 per cent less carbon than standard concrete. Nick Jackson, architect and project director, Arup
1 Triton Square was originally designed by Arup for British Land in the 1990s. Twenty years later, we returned to our original partners to sustainably expand and adapt the building for today’s work styles, with an overriding commitment to re-use, rather than replace, wherever possible.
There was a clear and genuine commitment to collaboration, thanks to a shared vision that was amplified by each party’s excitement to change the status quo. Demolishing the building and creating something new might have been the easier option, but we took a circular economy approach, considering how much could be retained and re-used. The project team rose to this challenge – innovating to keep as much of the existing façades and superstructure as possible while adding three extra floors and increasing the lettable area of the offices by 57 per cent, all without increasing the amount of plant space. This amounted to substantial construction cost savings and faster development process compared with a like-for-like new build. For instance, the circular façade cost 66 per cent less than a new equivalent.
To find marginal gains that improved performance, every aspect of the project was challenged to save carbon, cut waste and deliver an optimum working environment. A whole life carbon assessment was made using the RICS framework, and the refurbishment achieved a BREEAM Outstanding sustainability score at design stage.
1 Triton Square is ground-breaking because the whole team was willing to look at the world differently and collaborate to drive positive outcomes. Tim Downes, development director, British Land
All elements of the engineering in the building focus on efficiency, whether for programme, carbon or water. These include:
• Lightweight new construction and efficient structural design. • Lightweight roof plant (heavy plant in the basement). • Lightweight steel-framed infill. • Existing imposed loads to free up capacity. • Wind loads doubled with additional height. We were able to work with our wind team to justify minimum loads. • Fibre-reinforced plastic strengthening to circular reinforced concrete columns for programme and area benefit.F
Building services design required accurate co-ordination to fit plant for double the net internal area within the same plant space, with basement, roof and cores maxed out. Key co-ordination areas included services to and from the existing cores while ensuring floor-to-ceiling heights and plant replacement requirements were not compromised. Tight at all floors, this was especially tricky on the new upper floors, where the floorplate steps in, reducing the available zone for services, particularly at roof level. Water-based cooling towers were used for energy and space efficiency on the roof.
Water efficiency was also key. With London’s demand expected to exceed supply within 10 years, we were able to reduce our potable water consumption by 66 per cent by capturing rainwater from the roof and collecting grey water from the cycle showers.
Re-use of the existing external ductwork distribution ensured circular economy principles were also incorporated, with the overall engineering approach making a significant contribution to the BREEAM Outstanding score. Kate Fletcher, associate director and MEP lead, Arup
The original façade was a performance-led, integrated mechanical/façade system, featuring a pioneering double skin: a single-glazed outer screen, which modulated solar gains; and an inner screen of double-glazed ribbon windows, which insulated the building. We found it was able to meet today’s energy and sustainability requirements and achieve the BREEAM Outstanding target rating. We assessed the design life of the outer screen and whether to refurbish and reinstall or replace various elements.
The demounted lightweight prefabricated units were disassembled, cleaned, inspected and returned. End-of-life components such as gaskets and seals were replaced and the glass and framing kept. New panels replaced the glass and carrier frame of the internal screen.
New façades were designed for future disassembly. Glazed unitised curtain wall systems included vertical and horizontal external shading features in glass reinforced concrete or anodised aluminium, sized to reduce solar gains. The same lightweight unitised system supported the new limestone cladding to avoid significant reinforcement of the structure. We returned to the quarry where the original Val de Nod limestone was procured. A cleaned original stone sample was compared with the new stone to determine an acceptable colour range and a placement programme ensured there was no apparent distinction between new and existing panels.
As-built drawings were fundamental to our understanding of the original system, its performance and reinstallation to its original function. Robust design and construction documentation, from the original as-built records to the new façades, mean that the building will be adaptable in the future. Matteo Lazzarotto, senior façade engineer, Arup
Start on site March 2017 Completion May 2021 Gross internal floor area 47,195m² Construction cost Undisclosed Architect Arup Client British Land Structural engineer Arup M&E consultant Arup Quantity surveyor/cost consultant Aecom Project manager M3 Consulting Principal designer Arup (pre-construction), Lendlease (during construction) Approved building inspector Butler & Young (now rebranded as Socotec) Main contractor Lendlease CAD software used Revit Annual CO2 emissions 465 kgCO2 e/m2/yr (embodied carbon), 250 kgCO2 e/m2/yr (operational carbon estimated over 20 years) Façade engineer Arup Façade contractor Permasteelisa Group UK and Josef Gartner Atrium rooflight contractor OAG
Tags Arup British Land Building study Retrofit Technical study
“Located in British Land’s fortress-like Regent’s Place campus” Interesting given that was the criticism of the Euston scheme fo the 50s and 60s it largley replaced
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