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It鈥檚 the grass between the tramlines that makes all the difference. In British cities, the gap between the tramlines is covered in blacktop, but in the South German city of Freiburg, tramlines are almost entirely concealed by a carpet of green. The grass is not only there to make the streets look better; it is part of the sustainable urban drainage system and, more importantly, it halves the noise from the trundling trams, which means a much quieter life for nearby residents.

You can see these kind of details everywhere in Freiburg, and they have helped to make the city a popular destination for a special type of tourist 鈥� the one with an interest in sustainable architecture and placemaking. Freiburg has become Germany鈥檚 eco-capital over the course of the past 20 years, and now about 35% of residents don鈥檛 own a car, new homes routinely incorporate photovoltaic panels and even the Best Western hotel鈥檚 bedrooms have low-energy minibars.

Staff from PRP Architects and a handful of their clients made the pilgrimage to Freiburg this autumn to see what lessons the city held for UK housebuilding. They were wowed by what they saw. 鈥淚t wasn鈥檛 the individual innovations that caught our eye, it was the whole package of measures and how they are put together that was impressive,鈥� says Andrew Mellor, associate with PRP, who sits on the company鈥檚 in-house sustainability steering group. What stood out in Mellor鈥檚 mind was the grass in the tramlines; the Caf茅 Velo, which combines bicycle parking and rental with repair services, a caf茅 and a public transport information centre; and the fact that solar technology is not simply parked on rooftops but is often integrated into building design, with solar hot-water tubes serving as balcony panels, for instance.

The architects鈥� whistlestop tour took in the city鈥檚 best-known house, the Heliotrop 鈥� a building that revolves to make the best use of solar energy 鈥� and the Solarsiedlung (Solar Community), which contains the latest addition to Freiburg鈥檚 solar architecture 鈥� the mixed use Sonnenschiff (Sun ship) development. These and other buildings in the city are designed by German eco-architect Rolf Disch, who lives in the Heliotrop himself.

The Heliotrop is the city鈥檚 green icon, but it is hardly a model that could be widely applied in the UK. Built about a decade ago, the house produces roughly five times more energy than it uses. However, it did cost the equivalent of *2.2m (拢1.5m) to build, largely because of its revolving technology - its 54 m2 rooftop photovoltaic array revolves to catch the sun鈥檚 rays, while the house itself rotates in the opposite direction to maximise solar shading.

The new Sonnenschiff development is perhaps a more appropriate model for the UK, with its high-density mix of uses wrapped in an environmentally conscious building (see 鈥淲hat鈥檚 so sustainable about Sonnenschiff?鈥�, above). The 125 m long mixed-use building combines 1160 m 2 of retail space at ground floor, with 3600 m2 in two floors of office space. Above that there is 1160 m2 of living space in the form of eight 112-300 m2 houses. Car use is by no means prohibited, as the scheme incorporates 112 underground parking spaces, plus 28 on ground level.

Like all homes built in Freiburg, the Sonnenschiff houses conform to one of three energy-efficiency standards, all of which are higher than German norms (see 鈥淓nergy standards for housing in Freiburg鈥�, above). These standards are imposed by the local authority, which owns much of the development land in Freiburg. The standards are also, crucially, endorsed by the local community in a willingness to pay a premium of up to 3% for a sustainable home. Freiburg locals were converted to the benefits of buying green by the prospect of having a nuclear power station built in their midst. They won a battle to halt the project, leaving a shortfall in the region鈥檚 energy supply pipeline and generating a demand for environmentally friendly alternatives. Now the city produces about 65% of its energy from photovoltaics and combined heat and power, in the process saving 28 GJ of energy and 2100 tonnes of carbon dioxide a year.

As for Mellor, he came away from Freiburg with a conviction that it is people, rather than technology, that make sustainable communities happen. 鈥淲e learned that it is not impossible to implement sustainable measures, but that it does need the support of the local authority and residents. The key to Freiburg is that the local people wanted this and the local authority had to do it,鈥� he says. With the UK entering its own debate about the need for nuclear power, could homebuyers and local authorities here one day learn the same lesson?