The modern seaweed house of Læsø, Denmark

Ever since I saw photos of the seaweed thatch homes of Denmark in the book Built by Hand, I’ve been captivated and wanting to learn more about these unnusual structures. Recently, I was disappointed to learn that there are only about 19 traditional seaweed homes left standing on the island of Læsø. But, my disappointment turned to enthusiasm when I learned that some architects and builders are once again rejuvenating interest in the use of seaweed in construction. In fact, there’s been one successful newly built seaweed house, inspired by a competition organized by Realdania Byg. The results are very cool.

A renovated seaweed thatch home

Traditional Seaweed Thatch Homes

Sadly, the island of Læsø became largely deforested during the Middle Ages, as the island was home to numerous wood-hungry salt kilns as part of the once-booming local salt industry. The dearth of trees meant people turned to the ocean looking for new building materials, and driftwood and seaweed became the predominant materials to build homes for the next couple of hundred years. It was a rather ingenious discovery, as the seaweed made a naturally long-lasting and insulative thatch.

This seaweed thatch needs a little haircut…

Thanks the seaweed’s high salt content, the material is essentially fireproof and can weather time extremely well. In some cases, seaweed has been known to last hundreds of years, at least two hundred or more. (Compare that to the less than 50 year lifespan of a straw thatch roof.)

Another sad turn of events in the 1930s left inhabitants of Læsø unable to keep the tradition of seaweed thatch going. A disease overtook the local eelgrass, making it difficult or impossible to maintain the old homes. However, some forward- (and backward-) looking individuals are once again experimenting with the use of seaweed as an insulator, and roof and wall covering.

A newly built seaweed house, made with wood and seaweed almost exclusively

The Modern Seaweed House

In this excellent Youtube video (see below), architect Søren Nielsen discusses his team’s approach to the modern seaweed house challenge. The video goes through the process of sourcing, processing, and building with the eelgrass to create a modern interpretation of the traditional home of Læsø. Using mostly wood and seaweed, the team designed and built a fully seaweed-insulated home that is ultimately CO2 negative — that means the house accumulated more CO2 than was used to actually build it. Impressive.

Harvesting (eelgrass) seaweed for building

The design is definitely more modern-looking than the traditional examples, but I appreciate how fully the designers and builders implemented the seaweed in construction. It is certainly more than a fashionable flourish — it’s the basis for the entire building’s insulation, roof and exterior wall surfacing. The insulation value, and the amazing longevity and weather protection has been fully exploited.

Seaweed panels are raised into position

The team essentially built SIPs, in this case “seaweed insulated panels” that could be built on the ground and then shipped to the site. The wall frame is stuffed full of dry seaweed (not too much, nor too little to maximize the insulation value), and then sealed with what looks like some kind of sheet good. The panels are raised on site, and then finished with wood on the interior, and seaweed coils on the exterior.

Making seaweed coils for the roof thatch and exterior walls

The finished seaweed house exterior

The final product is a clean building with a unique exterior, and a very modern interior that would be difficult to distinguish as being stuffed full of seaweed. I like that the ceiling finish is another nod to seaweed stuffed mattresses of old, with the soft linen finish surface hiding the seaweed above.

Inside the modern seaweed house of Læsø

Seaweed house interior with skylights

Linen ceiling is a nod to traditional seaweed-stuffed mattresses

Seaweed house exterior

It just goes to show that we are surrounded by possibilities, and it’s only an issue of whether we can develop the creativity and willingness to develop natural materials into functional, beautiful spaces. Often, the answers lie in the past, and it’s a matter of adapting what our ancestors have already accomplished into something that can work for this time and place. I hope this seaweed house serves as a good example of that notion.

More photos can be found at Realdania Byg.

Thanks to Natural Homes for their excellent seaweed house feature.