Design for Living: The anti-flood forest and half-houses of Chile

The half-houses of Chile's Alejandro Aravena, in the city of Constitucion.

In 2010, a massive earthquake struck Chile, generating a tsunami with 6m waves. In the coastal city of Constitucion, near the mouth of the Maule River, more than 100 people died and 80 per cent of the buildings were damaged or destroyed. The Government quickly decided it needed to build a big sea wall, so they called in Chile's most famous architect, Alejandro Aravena, and gave him 100 days to come up with a plan.

Aravena built a house in the main square, hired a firm with skills in participatory democracy, sent in a team of young architects and invited the citizens to come and talk about what they wanted.

It was real participation: the people got angry and yelled at the architects. And what they revealed was unexpected. "Mr Aravena," they said, "it's very nice that you want to build a sea wall against the tsunamis, but we don't care about that." They hadn't had a tsunami for 60 years and they weren't expecting another any time soon. They had other problems.

The city flooded every year. There was almost no public space. And, while losing their homes had been terrible, they weren't fond of the buildings. "It's a pity the old buildings fell," they said, "but our identity is not connected to architecture. Our identity is connected to geography – to the river." Problem was, a few wealthy families owned all the river access. Ordinary people weren't supposed to get near it.

Construction firms lobbied for the sea wall. But 90 per cent of the public voted for a different idea: a forest.

It would be a park, tripling the city's public space and providing access to the waterfront. And it would disrupt the floodwater: the trees, along with some new lagoons and an undulating forest floor, would dissipate its force.

So that's what they did. As they like to say in Constitucion, it's about living with nature, not fighting against it.

Constitucion after the tsunami.

Constitucion as it will look when the forest has grown.

As a bonus, Aravena's company, Elemental, designed some public buildings, including a cultural centre, that people really could be proud of.

And on a tiny budget, they built a lot of half-houses. "What do you do when you have so little money?" Aravena says. "The traditional answer is that you build small, poor houses. But we decided that instead of building a bad house, we would build half of a good house."

Elemental's half-houses have half their volume built, and sometimes have a big wide roof over the whole space. The owners are at liberty to fill in the rest if or when they like. It's an approach they've used successfully in other parts of Latin America.

The participatory democracy wasn't popular with officials: Aravena says they thought it would slow the process and make it more expensive. But in Constitucion they used it to identify the right questions to ask (What's the real problem here?) and it worked.

What will we do about our own threatened coastlines? And just as important: Do we have robust enough democratic processes to decide?

More half-houses by Chile's Alejandro Aravena.

Design for Living is a regular series in Canvas magazine.