Danish Thatch For The Future

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Danish Thatch For The Future

Roofs made of seaweed called eelgrass have been in use on the island of Læsø in Denmark for more than 300 years. Will this thatching consisting of thick, heavy bundles of silvery seaweed be the solution of tomorrow? Read more about the Danish thatch for the future.

The roofs on the 1.800-person island of Læsø are up to a meter thick and hanging over the walls of the houses, they appear to be wearing a cloak. Seaweed is far more durable than thatch and might have the potential to be a contemporary building material around the world.

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Danish Thatch For The Future
Højsande on the 1.800-person island of Læsø. Photo: Wikipedia

Old traditions
Seaweed thatching began on Læsø in the 17th Century. Eelgrass grows on the island’s seas and were once so abundant that it frequently washed up on the shores. They have long, bright green, ribbon-like leaves about a centimeter wide, and up to 2 meters long. Farmers would collect them from the beach and once dried, they were bundled and twisted into thick ropes that were then woven through a home’s rafters to form a roof. Traditionally, weaving bundles of seaweed together was done by the island’s women folk. As many as one hundred women and young girls would take part in the activities. In the late 18th century there were 250 homes and farms thatched with seaweed.

Danish Thatch For The Future
The roofs are up to a meter thick and hanging over the walls of the houses. Photo: Visit Nordjylland

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A heritage project
In the 1930s a disease attacked the Island’s eelgrass making it difficult to maintain the roofs and now there are only 36 left. In 2009 a heritage project to save Læsø’s seaweed homes was established. Part of the project was to teach farmers in the south of Denmark to harvest and prepare eelgrass. A so called ‘Seaweed Bank’ was created to provide the materials to re-thatch the remaining homes.

Eelgrass is a very interesting material because it won’t burn: there’s too much salt in the straw and a thatch can last up to 400 years. As the roof ages it solidifies into one solid mass that is not only waterproof, but fireproof as well and can be trodden over without causing damage. It is also rot- and pest-resistant, but not only that. It also absorbs CO2, and as it doesn’t require heat to produce, is carbon neutral when harvested.

Danish Thatch For The Future
Eeøgrasshouse at Hærø. Photo: Vandkunsten

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Danish thatch for the future?
Today, the island has been reforested and residents can no longer see the sea from their rooftops. Many houses are surrounded by trees, protecting them from salt-laden winds. The Copenhagen-based American architect Kathryn Larsen is currently researching how the seaweed thatching on Læsø could be updated to contemporary sustainable building material.

Feature image (on top): Eelgrass roof at Læsø. Photo: Wikimedia commons

Danish Thatch For The Future, written by Tor Kjolberg

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