The Modern Seaweed House

Off the coast of the Danish mainland is a small island named Læsø renowned for its rich biodiversity and history dating back to the Neolithic Age. The island of Læsø is home to The Modern Seaweed House, a case study in sustainable architecture and advocate for seaweed as a modern construction material.

Botany and Læsø’s history are inextricably connected, and The Modern Seaweed House is but another addition to an architectural vernacular defined by the inventive and sustainable use of seaweed. Læsø was once home to hundreds of seaweed houses but today, this number is closer to twenty. This dwindling figure was the impetus for Realdania By & Byg — a non-profit organisation dedicated to the preservation of Danish building heritage — to engage the design expertise of Vandkunsten. This Copenhagen-based architecture firm took material cues from Læsø’s traditional construction methods and combined with a contemporary building approach, brought The Modern Seaweed House into existence.

Vandkunsten didn’t aim to replicate the existing vernacular, and rather than cloaking the home in seaweed (eelgrass to be more precise) as per the traditional construction method, The Modern Seaweed House is instead clad in netted pillows stuffed with seaweed, which were fixed to the timber frame in horizontal rows. Vandkunsten devised a further use for the seaweed, enclosing it within wooden casings and implementing it beneath the facade and floor as insulation.

Seaweed has a long history on Læsø. The shores of the small, 118m2 island are met by seaweed every day. The ocean produces it, and then reproduces it. It drifts onto Læsø’s sand and is dried by sun and wind. It is a material without human intervention, and perhaps ultimately, the most sustainable material when applied in a building context. The residents of Læsø have been utilising seaweed material for centuries and not just because it is free and found on their doorstep. It was also determined that the material was enduring and possessed several other properties that make it appropriate for building.

“Eelgrass has an insulation value of 80% of mineral wool when optimally compressed,” says Vandkunsten partner, Søren Nielsen. “It is non-toxic. The smell is very pleasant, like fresh hay. It does not attract pests, besides some birds who like to nest in it. It can be burnt passively, but it cannot flame and does not nurture fire. The acoustics are great and make it suitable as a noise-absorbing agent.”

LCA (life-cycle analysis) calculations indicate that The Modern Seaweed House has a negative footprint because of its predominant use of organic materials which trap more CO2 than the amount emitted during material production and transportation. But it’s not just seaweed that makes this home sustainable. The collaborative and holistic approach of Vandkunsten and Realdania By & Byg ensured emissions were further reduced through various means, during the entire construction process. The now holiday home was designed with disassembly in mind to mitigate waste at the end of its life cycle, while prefabrication was effective in reducing both financial and environmental construction costs.

Seaweed seems too good to be true. Vandkunsten has aimed to reintroduce the material to the broader building industry in hope of it becoming more prevalent. It’s been years since The Modern Seaweed House was realised and you would expect it to be taking over the building industry by now, cladding entire townships across the globe and not just twenty-something homes on a small island north of Denmark. But unfortunately, that’s not the case and it remains a niche product of little significance.

“Only two farmers in Denmark harvest seaweed,” remarks Nielsen. “Their entire production is bought by the Seaweed Bank, established by Realdania By & Byg, to be used for the renovation of Laeso’s seaweed-thatched buildings. There is however, an enthusiastic entrepreneur named Kathryn Larsen who is developing seaweed-based products. But this is the only example I know of.”

The Modern Seaweed House is an outstanding achievement in sustainable architecture, despite its broader reception as a mere curiosity. It’s a story of a remarkable material and its renewed use on an island with an extraordinary building history. The structure is at one with nature both visually and materially, and as we push onward into the environmental challenges of the 21st century, we must derive its lessons.

“The Modern Seaweed House acts like a crystal ball,” Nielsen observes “that catches and illuminates many of the most important issues the construction industry is facing today.”