London’s most eco-friendly building

It might look like just another modern corporate HQ but 7 More London, the last piece of the More London office development next to Tower Bridge, is the most eco-friendly building in the city.

At least, that's according to the Breeam sustainability assessors. Rigorously assessing against a bewildering array of criteria, Breeam (Building Research Establishment Environmental Assessment Method) is the Michelin star system for eco-friendly buildings. Holding a Very Good or Excellent rating is a badge of honour. 7 More London, which will be occupied later this year by management consultancy firm PricewaterhouseCoopers — its fourth London office — is the first building in the capital to achieve an Outstanding rating, and only the third building in the country.

Architects such as Lord Foster, who peddle crystalline, all-glass office buildings to big corporations, are caught in a double-bind by the need to limit carbon emissions. On one hand, glass buildings are great because they allow light in, limiting the need for electric lighting. However, they also magnify the heat of the sun, creating a need for energy-sapping air-conditioning. Foster wasn't the first to do all-glass buildings but he's responsible for some of the best and most influential, from his seminal Willis Faber Dumas headquarters in Ipswich (completed 1975) to the Gherkin.

Can Foster's trademark style survive ever more onerous pressure to create energy efficient buildings? Into the middle of this debate enters 7 More London, the result of a grand collaboration between PwC, Fosters, developer More London, architect and environmental engineer BDP and a variety of other consultants. All were determined that the building reach the Outstanding mark, and the ways it has done so reveal both the possibilities and the limits of designing low-carbon buildings in urban environments like London.

Apart from a Hilton hotel on the site, the More London development consists of six large office buildings by Foster and Partners (seven if you include City Hall), on a masterplan also by Foster. Number seven doesn't look much more eco than any of the others, with its glossy façades exuding that super-professional and slightly inscrutable identity typical of late Norman Foster buildings.

The first clue that it is different from the others is its lack of a grand internal (air-conditioned) atrium, a feature beloved of new office buildings from Canary Wharf to the City. 7 More London replaces that gesture with a grand entrance (facing the river) flanked by two dark glass wings and oversailed by curved bridges. From outside the front door you can just make out another space beyond those bridges, which turns out to be a private garden in the heart of the building, an interior courtyard, bringing light into the centre of the office floors.

Behind these architectural gestures is an energy strategy that is the basis of this building's low-carbon credentials. The building relies for power on a biodiesel-fuelled combined heat and power plant in the basement. This mini power station heats the building and uses waste heat to power refrigeration when cooling is required. The office interiors are heated and cooled by radiance systems using natural air convection, meaning a fresher and healthier interior environment than ordinary air conditioning.

Enclosing all this is a tautly engineered skin of high-performance glass, shielded from the sun by louvres of various kinds. Foster and Partners' response to the problem of combining large walls of glass with searing sunlight is to carry on designing glass façades, but to cover them with louvres. This is a trend that has already begun to produce a generation of striped office buildings (see Nicholas Grimshaw's UCL Cancer Institute near Goodge Street, for instance). At 7 More London, the Tooley Street face is covered in full-height vertical louvres in a burnished maroon colour (relating them, says the architect, to the colours of the adjacent brick buildings).

The serrated east and west façades also have silvery vertical louvres, just widely enough spaced to avoid the look of bars on cell windows. The building will reveal its ecological performance to PwC workers when they move in more explicitly than to passers-by. Perhaps the most interesting of these measures is the integrated IT system, which will enable each worker to control the light and temperature of his or her area of the office from their desktop computer. This means that the company can also (theoretically) track who's thrifty and who's wasting energy.

Management consultants, who fly thousands of miles every week, being encouraged to turn down the heating is palpably ironic. PwC does have a sincere commitment to reducing its carbon emissions but all the technology at 7 More London can't conceal the feeling that something is awry with making this building London's exemplar of sustainable architecture. Despite the energy efficiency, this is still a hermetically sealed, air-conditioned office building. It emits 55 per cent less carbon than a building built to normal building regulations and while this is good, the journey towards low- and zero-carbon buildings does not end here.