The treatment of the glazed facade of Arup Associates’ Ropemaker Place office development employs architectural means to environmental ends, writes Hattie Hartman
The facade of Ropemaker Place incorporates five shades of indigo. This subtle attention to detail permeates Arup Associates’ recently completed speculative office development for British Land in the City of London. Everywhere you look, it shows. Arup Associates practice leader Declan O’Carroll says: ‘Our ambition was to re-explore glass as a 21st-century sustainable material, yet retain its sensuous and poetic qualities.’ The fact that the building is rated BREEAM Excellent with 72.7 percent score, and was pre-certified LEED Platinum (Shell and Core),comes as an afterthought.
It’s unusual to engage in a discussion of an environmentally high-performing building that is about architecture rather than a litany of sustainable features. Arup Associates director Mick Brundle describes the massing as a series of interlocking cubes that respond to the site context. Reaching 20 storeys at the front of Ropemaker Place, with the core pulled to the perimeter, the81,200m² building steps down to six floors on the north side to relate to existing buildings – as required by planners. Floorplates range from1,100m² to 4,000m² and were designed to be flexibly combined to suit different tenants.
The architect worked hard to provide more than just office space. Mechanical plant is carefully relegated to the basement and uppermost roof to liberate remaining roofs for gardens each time the building steps down. The result is four terraces elegantly planted with a changing landscape of perennials by Townshend Landscape Architects. Views of the City of London are stunning. Similarly, a five-storey atrium is carved out of the northern side of the plan to bring light deep into the building and create asocial space for larger gatherings. To maintain flexibility, the atrium can be filled in to meet tenant requirements.
The entry sequence does not disappoint. ‘We wanted to grab the plaza on the approach from Moorgate,’ says Brundle. The soffit of the two-storey entrance comprises bespoke‘ gull wing’ light diffusers that form an elegant canopy by day and serve as a beacon by night. Eschewing the brashness of many City lobbies, the main visual feature is a timber wall veneered in FSC-certified European walnut. The entire wall was sourced from three trees in Switzerland and processed in the German forest where Snow White is said to have lived. But the real stroke of genius in this building is the treatment of the glazed facade, which employs architectural means to environmental ends. ‘We wanted to use the building skin like gills on a fish to reduce loads before employing renewables,’ says O’Carroll. It is not exactly like gills on a fish because the building is fully sealed. Natural ventilation was ruled out due to cost and acoustics, and also because, according to Brundle, the market in the City is not yet ready for it.
Solar gain is reduced by the use of projecting windows, tilted away from the sun on the east, west and south facades, and by the extensive use of opaque panels that comprise more than half of the facade. The projecting vision glass panels reduce peak cooling demand by up to 27 per cent compared with a flat facade, and consequently plant size is smaller, too. The pattern of the tilted windows eliminates the monolithic effect of the glazed facade, which is further animated by the use of optical lenses in the opaque panels. They act as prisms and reflect light differently depending on the amount of sun and the time of day. Here the five shades of indigo, selected from the Swedish NCS-System after colour studies by artist Antoni Malinowski, come into play. Understated monochromatic indigo tones were chosen instead of polychromatic schemes.
The key to this building’s success is that sustainability was driven through the project in an iterative process between client, designer and construction manager, Mace. For more than five years, Arup has drafted the sustainability brief of British Land’s corporate social responsibility policy, so mutual understanding underpinned the project from the outset.
The priority was to design an airtight, thermally efficient envelope and then use renewables. These include a 1,200kW wood-pellet biomass boiler and 75m² each of solar thermal and photovoltaic panels. These are estimated to provide between 12 and15 per cent of the building’s energy demand, well exceeding the 10 percent requirement of the London Plan. Ground-source cooling was ruled out due to the building’s small footprint. With the biomass boiler in operation, all hot water and space heating will be provided by renewable sources. Currently two dual-fuel (gas or biodiesel) boilers are in use rather than the biomass boiler, because gas costs less than wood pellets. To address tenant energy consumption, a metering strategy allows occupiers to monitor small-power electrical consumption separately from lighting and other loads on a real-time basis.
British Land recently commissioned two studies to examine Ropemaker Place’s as-built carbon footprint and to clarify the thorny issue of how energy and carbon are shared between owner and occupier. The landlord/tenant breakdown proved to be about 50/50,while the total carbon footprint for the building’s construction, operation and demolition (assuming a 60-year life) is196,873tCO2e, which is roughly equivalent to the electricity required to run the London Underground for four months, according to British Land. Embodied carbon comprises 42 percent of the total. But if the national grid decarbonises as planned, embodied carbon impacts would increase to 68 per cent – a clear sign that greater attention will need to be paid to material specification in future to drive carbon footprints down, particularly steel and concrete. Some say glass buildings are vestigial, but Ropemaker Place suggests otherwise. If thoughtfully designed, glass may not be dead after all.
Start on site October 2006
Contract duration 30 months
Gross internal floor area 83,600m2
Form of contract and/or procurement Bespoke Construction Management
Total cost £155 million
Cost per m2 £1,855
Client British Land
Architect Arup Associates
Structural engineer Arup Associates
M&E consultant Arup Associates
Quantity surveyor Sense
Planning supervisor Confluencepcm
Main contractor Mace
Annual CO2 emissions 24.6kg/m2