Beyond petroleum? This new headquarters for BP in Cape Town explores an agenda of environmental and social responsibility.

The validity of sustainability in the construction industry is often regarded with suspicion as mere lip-service to the greater green debate. When it is propagated by a petroleum company, suspicion turns to incredulity. So the new head office for BP Africa in Cape Town elicited great interest, especially among the architectural fraternity. But BP stated its approach quite simply: their offices have an impact on the environment, so it follows that if they make and use them in a more sustainable way that impact can be minimised.

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In the South African context, sustainable development means more than tackling environmental issues or the provision of a comfortable working environment by familiar passive means. It means addressing social and economic issues through skills transfer to people who did not have the earlier opportunity to gain experience in a specific field, so creating jobs. BP and the Victoria & Alfred Waterfront (V & A) also specified the use of locally sourced material through which the immediate community could be involved in the construction process. Black economic empowerment (BEE) is a further key target.

The new building lies on the edge of the Waterfront development, bridging the transition from harbour to city, with views to Signal Hill, the city and Table Mountain. KrugerRoos won a limited competition and joined forces with Green by Design Architects as environmental consultants. To comply with BEE targets, KrugerRoos also entered into an association with Joshua Conrad Architects and employed a team of resource consultants.

The competition called for an environmentally sensitive building and in a separate brief by Arup Associates principles and targets were spelt out in detail. Annual energy consumption was set to be 115 kWh/sqm, 10 per cent of overall energy had to come from renewable sources, water consumption must be 20 per cent better than an equivalent conventional building. Local (rather than imported) and recycled materials were to be used, construction waste was to be recycled, and an environmental management plan for the construction period had to be submitted. The T-shaped building is orientated at a 45 degree angle to the north with the main entrance on the south-east corner. The bulk of the building consists of open-plan offices with ancillary spaces such as meeting rooms, a coffee shop, gym, medical suite and travel agent. These functions are arranged around a triple-height circulation volume divided into three distinct zones. Visitors and employees alike arrive in the reception area. Accompanied by BP employees, visitors may access meeting rooms and the coffee shop. Office space remains private.

Strategies were investigated to determine the best solution. Night cooling by way of rock storage was rejected due to the small diurnal temperature range, expense, space required and the need for a conventional back-up system. Taking advantage of the harbourside site, using sea water to cool the structure was considered, but it was found that the marina water temperature was rising and pumping water from a greater depth would require a much larger, financially unviable system. Solar cooling and phase change material technologies were too expensive and relied on imports, despite being technically feasible.

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The environmental performance of any building is largely determined by the design of its envelope. The architects developed a kit of parts to articulate each elevation in response to its exposure. Ventilation stacks at the building's outer edge allow the double-glazed windows to be deeply recessed, reducing solar heat gain in summer but allowing sun penetration of office space during winter. Light shelves in the recesses shade windows according to the season and reflect light into the deep plan. Dimmable fluorescent lighting supplements natural light when necessary. Rainwater is collected from the roof and hard landscaping, with air-conditioning condensate and a third of the building's waste water. This grey water is sand filtered and used to flush lavatories and irrigate vegetation. The recycling system should reduce municipal water consumption by as much as 75 per cent compared with a conventional building, a great improvement on the original target of 20 per cent.

Visible from the city and future buildings, the roof was designed as a fifth elevation. A series of lanterns along the circulation route provide natural light to the core in sufficient quantities for the rows of forest mahogany trees to grow, a species carefully selected for the conditions. Direct sunlight is eliminated by orientating glazed sides to the south-east. The lanterns also serve as vents for stale air and smoke outlets in case of fire. Thermal solar panels and photovoltaic cells, which generate 10 per cent of the building's electricity, further articulate the neatly ordered roofscape. The building is modest rather than loud, the palette of materials and details restricted, direct and intelligible. Money saved by eschewing expensive materials and equipment has been used instead to make architecture of simple clarity and meaningful quality.

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