On the Danish island of Laesø, once known for its salt industry, there still exist dwellings thatched with seaweed, also known as eelgrass. The walls of the homes were made of driftwood. Since both the seaweed and the driftwood were saturated with salt water, they survived for centuries. The seaweed houses still standing there have been declared as one of North Jutland’s seven wonders.
Eelgrass was traditionally dried, bundled, and twisted into thick ropes that were then woven through the rafters of homes to form roofs. Such roofs typically last 200 years, with some surviving up to 400 years. But in the 1930s, the eelgrasses natural to the area were attacked by a disease that made it challenging to maintain the roofs. The number of remaining eelgrass roofs dwindled to just a few by the 21st century.
Recently, the Modern Seaweed House, a $360,000 vacation home, was built in Laesø, incorporating seaweed-stuffed “pillows” on the building’s façade in the place of traditional shingles or clapboard. The algae was also stuffed into the light pine walls and serves as a replacement for mineral wool insulation. The ceiling is also padded with the same insulation. It was a collaboration between architectural firm Vandkunsten and Readania Byg, an organization that preserves Denmark’s historical properties. Designers estimate the exterior pillows could last 100 years or more.
Watch a presentation by Marcele Meier about the conservation of an eelgrass seaweed building: