Foster & Partners’ headquarters for Bloomberg is billed as the world’s most sustainable office building. What does that mean, asks Sofie Pelsmakers?


Sofie Pelsmakers

James Newton, Nigel Young

Around 4000 Bloomberg employees are moving into the technology and media company’s new 100,000-square-metre City of London office building, designed and engineered by Foster & Partners and AKTII. Michael Bloomberg, the company’s founder and CEO, was closely involved in the design and decision-making process, developing a demanding brief and pushing innovation on a complex site while also supporting a sense of civic responsibility to the city – generally rare on corporate projects like this.


Out is the generic glass-and-steel office tower, which tends to be the same across the world, regardless of climate, exposure or cultural setting. Instead a 10-storey building was conceived – the top two floors are set back – with crafted sandstone and bronze facades to match the surrounding context. (There is still a lot of glass, steel and concrete in the building, however; the majority of the previous 1950s building’s slab and pile foundations were re-used).

Rather than building right up to the edges of the 1.3-hectare plot, generosity is shown by cutting a pedestrianised arcade diagonally through the building and making three small plazas at its corners. The only sign of greenery, however, is a handful of young trees on the street. In a heavily built-up area with high levels of air pollution, not to have made more space for trees, green courtyards or a public roof garden seems a missed opportunity.


Almost 10,000 tonnes of British sandstone were used, and at certain areas of the facade, at ground level, there is a tactility, care and craftsmanship not easily conveyed in photographs. But some of the beautifully crafted stone curved ledges are already stained with water run-off marks, raising a question of how the building will age.

The building facade is punctuated by bronze fins, which give a rhythm to some public spaces around the perimeter at ground level, and turn into large “breathing gills” – natural ventilation and solar shading mechanisms – on the upper floors. The decision to naturally ventilate such a deep-plan building (each floor can hold 800-900 staff) is bold, and as yet untested in practice. A Building Management System monitors internal and external conditions and when they are suitable, opens the giant fins to provide fresh air. Warm, stale air is expelled at the top of a central void, through which an elliptical circulation ramp ascends. The system is intended to reduce reliance on mechanical cooling and ventilation, contributing to energy and carbon savings. It is not fan-assisted, and fresh air from outside is not filtered, which would reduce its air-change capacity. It remains to be seen how effective this will be in safeguarding internal air quality; though it will be supplemented by mechanical systems based on CO2 monitoring. The gills on each floor are differently acoustically attenuated depending on their location and exposure to external conditions, demanding an extensive and impressive understanding of appropriate design responses to different local context and micro-climates.


The use of the fins for solar shading also means that their spacing and orientation varies with their solar exposure. This leads to each facade being slightly different, which is still unusual for corporate office buildings of the recent past, but a basic starting point for sustainable architecture. Even with this subtle facade variation the architectural expression is perhaps overly controlled; the language is sufficiently robust that more differentiation could have been introduced, especially where the deep horizontal glass facade setbacks do not offer any protection from the low sun, yet compromise daylighting.

The opening up of the floor plates with as few columns as possible, and placement of innovative concealed-mechanism glass lifts against an external facade, create an open-plan but introverted environment suitable to the company’s collaborative and transparent work ethos. However, while these moves afford long views deep within the space, this inward-looking arrangement compromises natural daylighting and precious views and connections to the outside world.

An attempt is made to remediate this deep plan by a void in the heart of the building which contains a remarkable half-elliptical ramp connecting all office floors, and brings in daylight to the middle of the plan from the roof. However, due to the twisting ramp, natural light only effectively spills into the centre of the building on the highest floors. While a welcome variation in the lighting conditions on the upper floors, this effect is only very localised in the immediate area of the void, leaving thousands of occupants without access to natural light at their desks and only benefiting from daylight when in transit or in the generous community hub – ‘the Pantry’ – on the sixth floor.


Artificial lighting is provided by a unique aluminium ceiling system, whose 2.5 million petals act as a light reflector to 500,000 integrated LEDs, giving an energy saving of 40 per cent compared to typical office lighting. The system also provides acoustic attenuation, sprinklers and radiant cooling, all in a ceiling zone of just 100mm. It appears effective at providing a uniform 300 lux at desks without glare or reflection on screens – boosted by individual desk-lamps to about 500 lux. While this solution somewhat mitigates the absence of natural daylight, the lack of escape from artificial lighting might prove inadequate over time, especially as research suggests that LED light can affect our natural circadian rhythms and in turn affect well-being and productivity.


Balancing competing aims is always difficult in the design process, and in this case the interpretation of what it is to be a ‘good neighbour’ in the City, and the desire to cluster employees on similar floor plates to aid collaboration, might have been achieved at the expense of daylighting for occupants in the building itself. Yet these needn’t have been mutually exclusive; perhaps daylighting and viewing ‘cuts’ through the building could have been offset with additional storeys in a small area of the footprint, without compromising the architects’ urban ambitions.

It is however encouraging to see a focus on sustainability innovation in many areas of the building. In water use, for example, technologies employed include vacuum toilets, water capture and grey water recycling (though this can itself be energy intensive). Overall this effort is predicted to give water savings of about 70 per cent. Innovations in ventilation, lighting and cooling, alongside an efficient gas-powered CHP plant, are predicted to give total energy savings of about 35 per cent compared to similar office benchmarks. The CHP plant will burn fossil fuel to produce electricity, but the heat created as a by-product can be used for heating or cooling.


While these are significant improvements on benchmarks, a deep-plan building will still generally lead to a higher year-round continuous energy demand for low-energy lighting and ventilation and cooling compared to shallow-plan spaces which can be naturally daylit. Nevertheless, the energy and water savings outlined above, alongside excellent access to public transport, will have been major contributors to the scheme obtaining a BREEAM rating of ‘Outstanding’ at design stage, with a score of 98.5 per cent, making it the world’s best-rated office building (there are over 550,000 BREEAM-certified buildings around the globe).

Though the designers’ efforts in relation to energy use and water are admirable, there could have been further reductions in both operational and embodied energy (albeit limited by the deep plan). That a building can be judged ‘best in class’ despite the use of carbon-intensive materials, few views to the sky and lack of natural light illustrates the limitations of BREEAM. It also raises questions about BREEAM-certified buildings, and their usefulness as exemplars. Likewise, the fact that the Bloomberg building will save 25 million litres of water annually compared to typical buildings suggests that the benchmarks we are using are severely problematic in their obscene wastefulness.


Foster & Partners carried out extensive environmental building simulation modelling in-house, and its well-funded research allowed, for example, for the construction of part of the building at 1:1 scale in a warehouse ‘lab’, where it was exposed to standard and extreme climatic conditions, enabling the architects and engineers to refine the design and give them confidence in its performance. Similar 1:1 testing was undertaken for the petal ceiling system and the desk design.

This early in-house testing and validating at different scales (as close as possible to reality) alongside the multidisciplinary design approach is necessary for innovation and exemplary as a model for the rest of the profession and clients in meeting the challenges of climate change. Given the unusual level of investment, can the Bloomberg headquarters act as a new benchmark, against which future buildings should be measured, or help to shift practice elsewhere? Clearly the project relies on design processes that are not feasible for less-well-resourced clients. But when one of the world’s most highly regarded architects talks about how passive principles, such as solar shading and natural ventilation, generate an architectural language, this influences architectural debate and practice.


As a high-profile project, the Bloomberg building might encourage the mainstream adoption of vacuum toilets, for example. Other details also add to the store of knowledge that can be replicated. Natural ventilation added unanticipated complexity to the specification of internal finishes. To allow an oak finish to a raised access floor, for example, the architects developed a magnetic fixing that can accommodate material movement. The use of magnets had to be tested for interference with data cables (there was none once held down), and of course the introduction of magnetic fixings will increase the embodied energy of an otherwise low-energy material. This sort of problem-solving research, if shared widely and transparently (as seems to be the case) will help to enable the adoption of natural ventilation strategies in other buildings.

Foster & Partners is contracted to monitor the building in use through post-occupancy and building performance evaluation, obtaining feedback for further validation, alongside fixing any issues during the first few years. Hopefully this work will feed into the current research about open-plan office design and impacts on occupant wellbeing, health and satisfaction. Time will tell how truly sustainable this building is, both in meeting its energy objectives, promoting the wellbeing of its users, and allowing adaptation to meet changing requirements, and it is to be hoped that this knowledge will be widely and transparently shared.

If so, the Bloomberg headquarters could act as a new benchmark for office buildings, encouraging continuing innovation in this building type. Its completion could mark a turning point in the sector, by giving greater prestige to the sustainability agenda and generating confidence among other architects and clients that they might match – and ideally surpass – its ambitions.

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