For the first time in history half the world's population lives in cities. As pressure on living space grows, so does the need for affordable housing. 'City Scope' looks at some eco-friendly solutions - not all are in cities - but all could be used in an urban setting.

Reed All About It, The Netherlands

Just as the need for environmentally clean power re-launched cutting edge windmill technology, so the past five years have seen a major revival in a building technique many thought had no place in modern life: thatching.

In Holland there are over 300 companies specialising in thatched roofing. Far from being a dying art, new techniques have revived this industry which now employs around 1,000 people throughout the country.

Unlike other roofing products, like slate, thatched roofs use reeds which can be cropped annually. And unlike brick tiles, reeds do not need to be finished off in a kiln - saving valuable energy.

Thatching also saves energy in other ways. A thick thatched roof provides excellent insulation where slate tiles do not.

Once again, the past provides us with valuable energy saving lessons.

Shacking Up, South Africa

When the ANC was voted into power in 1994 'homes for all' was a key election promise. Several years later the housing crisis is still one of the government's biggest problems. Today, millions of people live in vast informal settlements.

The main danger is fire - which can sweep through informal settlements constructed from highly flammable scavenged materials like wood and cardboard.

Now a new project, sponsored by DFID, is helping residents of informal settlements make and build their own homes.

From casting bricks to constructing beams and crossbars, the residents take control of each step in the construction process.

But at 56,000 rand per home (US$4,000), that's more than most people can afford. Now a new savings scheme, run by People's Dialogue, is helping to speed up the process of building new homes. So far this micro-credit initiative has helped build 92 homes and there's funding for another 236.

For more in-depth information from the Hands On team, visit their website.

Timber not Termites, Sri Lanka

The coconut tree is one of Sri Lanka's natural treasures - providing milk, food and shelter. But the government is so worried about its decline that it's banning its use.

Hunger for cheap wood is so great that over the last 30 years an estimated one third of Sri Lanka's coconut trees have been illegally felled for timber. The resulting shortage now means that Sri Lanka has to import timber from South East Asia.

But as Sri Lanka's population grows it is essential to build low cost housing using locally available materials. Now TRADA technology have come up with an idea that uses thinnings from plantations.

Plantation thinnings make the perfect building poles - tall, straight and round. But before they can be used they must be treated to prevent termite attacks.

The total cost of a finished house is just US$600 - half the cost of one using imported wood. So far, one thousand timber pole houses have been built in Sri Lanka and it's a low cost technique that could be used in all over the world.

For more in-depth information from the Hands On team, visit their website.

Piping Success, Ecuador

Three thousand feet above sea level in the Andes of Ecuador the village of Cachi has a water problem. But it's not a shortage of water that's the problem. It's how to get water to a remote village in an earthquake zone without using underground piping that's been their challenge.

Their village lies on a geological fault-line that makes conventional water pipes impossible. But with the help of the International Fund for Agricultural Development (IFAD) the villagers came up with an unusual idea: an aerial system of passing water pipes through trees.

A system of valves and springs protects the pipes against ground movement from earthquakes and increased water pressure in the rainy season. Now the village has safe, clean drinking water all year round.

For more in-depth information from the Hands On team, visit their website.

Back to the Future, India

In the last series of Hands On we saw how low cost building techniques helped solve a chronic classroom shortage in Andra Pradesh. Several thousand schools later the project partners, DFID and the Andhra Pradesh Directorate of Primary Education were asked whether the techniques could be used to meet the urgent demand for hospital buildings in Orissa - one of India's poorest states.

In recent years India has turned away from low cost building in favour of more expensive modern methods and materials. To meet the demand for hospitals in the state of Orissa using conventional methods would cost US$150 million.

A unique partnership between the Government of Orissa and DFID has brought architects, engineers and skilled artisans together in a skill-sharing programme. Between them, new techniques have been developed which have dramatically cut the cost of expensive buildings like hospitals.

The disposal of flyash, a pollutant of the power industry, is a national problem in India. But flyash mixed with lime and gypsum can replace sand and make a strong building brick which has the added benefit of cutting costs by 15-20%. Using this method, flyash can be disposed of safely whilst also benefiting the construction of public buildings.

For more in-depth information from the Hands On team, visit their website.