Seaweed roofs on Læsø

Læsø island has historically been associated with salt production, which in the 17th century led to widespread deforestation.^[1] Reeds, that are traditionally used in many other areas as thatching, were difficult to transport to the island, and straw was too valuable as fodder to be used.^[2][3] At the same time, an abundance of eelgrass washed up on the shores of Læsø, and thus began to be used to build roofs. Surviving examples date as far back as the 1650s, and the last building to be built in this tradition dates from the 1870s. Subsequently no new buildings have been erected with seaweed roofs, but old buildings continue to be repaired using the traditional technique. While there were around 230 seaweed roof buildings on Læsø still in the 1930s, the total number in 2014 was by one account 34.^[1][4] As part of a conservation project, a new house with seaweed roof was constructed on Læsø in 2012–2013.^[4] The seaweed houses of Læsø are part of a proposed inclusion of the cultural landscape related to the historical salt production on the island as a World Heritage Site, which is on the Tentative List of World Heritage Sites since 2023.^[3]

Traditionally the construction of seaweed roof houses was done by women, who also harvested the building material, while the men of the island who were long periods at sea as fishermen would collect driftwood.^[1][3] Construction of such a house was a collective undertaking that could involve 40-50 or even up to 100 people.^[1][3]

Houses built with a similar technique have existed in Halland in Sweden, across the Kattegat from Læsø. No seaweed roofs however remain there.^[1]