In recent years, leaps in eco-friendly architecture have been spurred by technological innovations, such as walkable solar-powered flooring and “smart” houses that self-regulate cooling and heating systems.
But now scientists are rewinding the clock and discovering how 400-year-old roofs may hold the key to future decades of bio-based building materials.
The roofs in question are located off the coast of the Danish mainland on a large island named Læsø — and the town, despite being 11,000 miles away from New Zealand, looks surprisingly reminiscent of a Hobbit village from “The Lord of the Rings.”
The resemblance lies in the island’s mushroom shaped cottages, which are topped with 90-pound heaps of hand-spun dried eelgrass. Some of these homes, and their roofs, have survived close to 400 years, sitting untouched and undamaged despite weather and time.
And now scientists have found evidence that eelgrass isn’t just sustainable — and ultimately, biodegradable — it also stores massive amounts of carbon dioxide.
According to a 2023 report from the Environmental Protection Agency, eelgrass is capable of removing carbon dioxide from the environment up to 35 times faster than rainforests.
Back in the 17th century, eelgrass roofs were utilized out of necessity. Danish islanders had little to no access to timber and other building materials for their roofs, so they looked to the beach for alternative solutions, repurposing shipwrecked wood and miles of eelgrass.
Unlike seaweed, which is a type of algae, eelgrass is a flowering plant that grows in shallow waters and has thick, anchoring roots — something that has aided in keeping those eelgrass roofs so formidable.
The roofing process involved drying the eelgrass in fields for two weeks, bundling and twisting the eelgrass into thick ropes, and then weaving those ropes into the rafters.
“In the old days, you could build a roof in one day with help from up to 100 of your fellow islanders — women and children while the men were sailing,” Henning Johansen, one of the last “master eelgrass thatchers,” told Smithsonian Magazine.
Today, the emerging evidence of eelgrass as a carbon-storing architecture alternative has ignited newfound interest in the plant.
But Kathryn Elizabeth Larsen — an architectural technologist and co-founder of Reef Circular, a company that builds bioconcrete out of shell waste — has had her eye on eelgrass for years.
In a 2019 dissertation for the Copenhagen School of Design and Technology, Larsen combined eelgrass with seagrass plates to build structured wood panels with insulation, waterproof and vaporproof “membranes,” and timber posts. Her goal was to explore its potential in architecture.
“Imagine a building material that is rot resistant, fire resistant, non-toxic, insulates comparably with mineral wool, and can be used to create carbon negative buildings … this material has been used for centuries already around the world — until we forgot how to use it,” Larsen explained.
Her conclusion: “Eelgrass has an incredible potential as a world-wide building material.”
But future use of eelgrass relies on the conservation of the plant today.
“At the moment, the seagrass community is really looking at how we can create nurseries for seagrass to aid in the restoration of degraded meadows rather than for supplying construction or other activities,” Richard Lilley, founding director of a widespread restoration charity called Project Seagrass, told Smithsonian Magazine.
“There is a rationale for commercializing seagrass production, but ecologically sustainable production needs to be at the heart of that business model, and the numbers for doing that simply don’t add up at the moment.”
Lilley is right. The green, multi-talented plant has been through the ringer in the last century.
In the 1930s, a wasting disease almost wiped the eelgrass out completely in Læsø. And now erosion, coastal pollution, and human activity have led to another dramatic decline in the last two decades.
Fortunately, as climate scientists, engineers, and architects fund new research into the long-term protection of eelgrass meadows, locals in Læsø still have a large amount of “eelgrass wrack” washing up on their beaches — which is perfect for building those traditional “Hobbit-looking” homes.
“[It’s] important to acknowledge the ecological role of eelgrass for beach communities, salt meadows and for natural shore protection,” explained Dorte Krause-Jensen, a marine ecologist at Denmark’s Aarhus University. “So the wrack should also not be overly exploited.”
“However,” Krause-Jensen added, “where the wrack is in any way being removed to clear the beaches, it might as well be used.”
Header images via TrineBM (CC BY-SA 3.0) and Ingrid Taylar (CC BY 2.0)
