Ask what makes a design sustainable and you will receive many different answers. Some would say a building incorporating wind turbines and solar panels; others might argue thermal mass is the key.
Peter Bishop, first director of Design for London, believes the word 'sustainability' has been badly abused and should be expunged from the English language. "Sustainability should be exactly what it says, something which has the ability to perform satisfactorily over a long period of time."
In his current role, Bishop has the task of balancing the human, environmental and financial cost of design in the UK capital. "Achieving zero carbon is one of the main aims of developers in the Thames Gateway in London along with high levels of performance, local procurement, energy efficiency and, where possible, locally generated energy."
He is also targeting the city's carbon framework with £12m of energy audits. "How we use energy is more significant than things like solar panels, which are a long way off being economically viable. There are new technologies being developed, but we need to get more out of our existing ones when planning and designing new builds."
Elsewhere, Japanese architect Shigeru Ban's latest project, the Centre Pompidou-Metz in France, is exploring the sustainability of regional art. Once completed in 2008, the satellite gallery of the main Pompidou Centre in Paris will house three rectangular tube galleries, a creative studio, an auditorium and a restaurant.
Its most remarkable feature, however, is the roof – 8,000 square metres of hexagonal wooden units resembling the cane-work pattern of a Chinese hat. The structure will be covered with a waterproof membrane of fibreglass and Teflon, creating a controlled and naturally temperate environment.
For Ban, the concept of sustainability is an elusive one. "Everybody talks about sustainability, but I have a big problem finding the right answer." He says the cost of installing systems like solar panels can outweigh the energy savings for projects with a limited budget, describing it as 'a contradiction'.
A different approach has been taken by Terry Farrell and Partners (TFP), designer of the Green Building in Manchester, heralded as one of the most advanced ecological developments in the UK and winner of the Best Environmentally Sustainable Project Award at the 2006 LEAF Awards.
The mixed-use complex, featuring 32 apartments, a nursery, doctor's surgery and commercial accommodation, has a circular design with minimal surface area to volume, providing maximum insulation and energy efficiency. John Campbell, technical director at TFP, says some kinds of sustainable technology, such as solar panels, are little more than 'green' gestures.
"The return for these sorts of measures is still poor and they don't give value for money at this scale. We had to put up a large steel structure at the top of the building to support the panels in the correct orientation, along with gantries, ladders and handrails to provide maintenance access, all of which had to be craned into position."
Its component parts came from halfway across the country, with specialist labour getting to the site using petrol or diesel-driven cars. "It was a high energy spend for a green feature that does nothing but provide lighting for the communal areas," adds Campbell.
For Campbell, the definition of sustainability in the UK can be found in the Brundtland Report in 1981, which states: "Sustainable development is development which meets the needs of the present without compromising the ability of future generations to meet their needs."
Campbell believes sustainable design has to start with the basics, such as avoiding greenfield sites wherever possible, minimising new transport links and reusing existing buildings, but this is nothing new.
"On a more detailed level, it's about getting the design right from day one, so you are not adding or incorporating green features at a later stage," he says. "For all projects, we look at sustainability in the construction, development and design – we always have done – but sustainability has become a buzzword and now everyone asks what we are doing in terms of sustainability. We are not doing anything different; we have always incorporated the appropriate measures in our designs."
One project where sustainable design was a top priority right from the outset was the Home Office's headquarters in London. A key requirement of the brief was that the building should have a BRE Environmental Assessment Method (BREEAM) rating of Excellent, which it achieved with a rating of 9/10.
The construction had many green features: 50% of the construction materials were recycled, 90% of occupants are within 6m of a facade or atrium and the building has an energy-efficient facade for reducing solar gain and heat. A unique water energy transfer system also ensures redistribution of thermal energy.
"The building met higher targets than the standard thermal regulations but didn't use any particularly new technologies," says Campbell, who believes new technologies such as solar power still have a long way to go. He would also like to see more research into glass cladding incorporating energy active interlayers that react to heat, light and even sound.
Outside the UK, Hellmuth, Obata + Kassabaum (HOK) is another firm with sustainability at the top of its agenda. Director Andrew Barraclough says the key is getting the basics right early on. The firm uses Rebit, recently purchased by Autodesk, as a key tool in its initial analysis. "We use intelligent 3D modelling at a very early stage, so we can see how the building is going to behave as an organism,"says Barraclough. "It's so basic, yet so fundamental. It means looking at the form, how the building behaves, how air movement works through the building, how the heat is captured and reused, and looking for these things in every project."
One of the company's recent projects is the Darwin Centre at the Natural History Museum in London. The 'intelligent skin' has hundreds of louvers between the glass layers on the south-facing wall that track the sun; as they warm up, they draw air from ground level through a chimney on the top floor.
In addition, a self-cleaning Teflon duvet of ethylene tetraflouroethylene on the roof acts as the equivalent of triple glazing, with minimal structural support required.
Another notable project is Barclays Global Headquarters in London, which also achieved a BREEAM rating of Excellent. It has a green roof, a heat recovery system and five atria to maximise daylight and provide a thermal buffer. Materials were delivered by barge and 80% of construction waste was recycled.
A third project, offices at 40 Grosvenor Place in London, uses 20% less energy than comparable buildings – a combination of chilled ceilings, a high-performance skin, a displacement ventilation system and workspaces that are no more than 25ft away from natural light.
"It's about much more than being green," says Barraclough. "We were also trying to make sure it was an asset that had value over its lifespan. This is a much broader concept than just getting maximum efficiency from buildings."
Until we see more progress in research into energy-saving devices, it seems the key to sustainable design in the 21st century will be in allowing architects to return to core principles and build thoughtful, long-lasting buildings