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How to build a house from seaweed

Læsø, a tiny island off Denmark’s north-east coast, has been making homes from seaweed for centuries – we learn how

How to build a house from seaweed

Humans have built homes using everything from animal dung to ice. But who would think seaweed – that smelly, slimy material – would be good for building houses?

The inhabitants of Læsø, a tiny island off Denmark’s north-east coast, have been creating homes from it for centuries. “Læsø is the only place in the world where they are found,” says Jørgen Søndermark, architect at heritage organisation Realdania Byg. “In the 1930s you would find them all over the island. In 1973 there were 100, now there are only about 20.”

The houses were built using eelgrass, a water plant so abundant in the island’s seas it frequently washed up on its shores. Bright green, it’s a slim plant with leaves about 1cm wide and up to 2-3m long. “Farmers would get to the beach immediately, grab it with a tractor and dry it out in the fields,” says Søndermark. Once dry, “it’s brown and soft to the touch,” he says. “We’ve been comparing it to insulation fibres. It’s simply gathered like hay, rolled up in 250kg bundles.”

Traditionally used to create dramatic hairy roofs, eelgrass looks a lot like thatch. However, its natural salt content means it wards off unwanted animals who might fancy a bite, such as bugs, rats and lizards – with the right maintenance, roofs can last hundreds of years. “You’ll find some birds in it, though,” laughs Søndermark.

In the 1930s a plague wiped out Læsø’s eelgrass, meaning the custom began to die along with it. Recently, however, a group of islanders was keen to revive the tradition (eelgrass is still abundant in parts of the Baltic Sea) and Realdania Byg became involved. Its first project was to restore a listed house dating from 1850 that can now be rented, but the organisation builds experimental new buildings too, with a green bent.

Realdania Byg ran an architectural competition to design a new house made from seaweed on Læsø. The winner, created by Danish architects Vandkunsten, is a contemporary reinterpretation of the old seaweed houses. Built from prefabricated wooden cassettes filled with eelgrass to insulate the house, it is then clad with seaweed pillows created from around 800m of handmade woollen nets stuffed with eelgrass. “It was like making sausages,” laughs Søndermark of the relentless task. “That’s eight or nine tonnes of eelgrass,” he says.

The hope is to inspire others to build with the material. “We’ve helped establish a supply chain,” says Søndermark. “We should see the past as a great archive of building materials. Solutions that are old could be new.”


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