“Seaweed Girl” Kathryn Larsen on thatched roofs & architectural history

In this interview, Reframe’s founder Bridget Cogley talks with Kathryn Larsen, who goes by the name “the seaweed girl” on Instagram. She is pioneering seaweed research and design by reviving century-old techniques, and believes that by returning to vernacular architecture methods, the building industry can become more sustainable.

At 26 years old and an architecture student in the Netherlands, she has showcased around the world, from Venice and Copenhagen to Design Indaba 2020 in Cape Town. She also has a Youtube channel to educate people about architecture history and theory.

Photo by Anders Lorentzen

BC: I’m so excited to talk to you, and I love your Instagram. What’s your background, and what are you working on?

KL: I'm originally from the US, and I'm an architecture student at TU Delft in the Netherlands. I got into eelgrass as a building material while studying in Denmark (eelgrass used to be called seaweed but it is a type of seagrass). It was used to thatch roofs on the island of Læsø, Denmark, since the middle ages, but this thatching technique has almost been lost.

After working with eelgrass for several years, I came across the work of Julia Lohmann, and it inspired me to look at kelp and seaweed as a resource for interior design & architecture.

Photo by Kelley Hudson

BC: Before studying in the Netherlands, where were you?

KL: I met a Danish man in Japan in 2013; we got married, and I lived and worked in Denmark for 5 years. I was educated as an Architectural Technologist in Denmark at Copenhagen School of Design and Technology (KEA).

While studying there, I came across Læsø’s Seaweed Houses. I fell in love with the material and the thatching tradition and history. I have been working with turning it into prefabricated thatched modules, along with kelp's architectural applications ever since.

BC: So how would you describe your work? And what are you working on now?

KL: I look at the past and combine it with technology that we have now, to figure out how we can build for the future. Also, I like to build with seaweed and seagrass.

At the moment, I'm working on turning prefabricated thatched modules into an interior acoustic solution. I am also looking forward to my thesis at TU Delft, and how far I can push building with seaweed!

Before, in Copenhagen, I made Seaweed Pavilion as a way to explore developing modern seaweed thatch panels for the building industry. I also received funding after school to continue development, and one thing quickly became clear: There was a lot of prejudice against eelgrass, especially as a visible external material. Common questions included “will it rot” or “does it smell?”

A seaweed farmer, Kurt Schierup, from Møn Tang, specially prepared the eelgrass to create building grade quality. The farming and drying technique washes away the micro-algae, and makes the eelgrass rot resistant. The resulting eelgrass smells similar to grass.

Photo by Kelley Hudson

BC: What do you think is the one major thing that needs to happen to promote sustainable design?

KL: We need building regulations to account for how much CO2 emissions buildings create while being built, and then emit for the years after they are built and are in use, because the building sector is responsible for a whopping 38% of global emissions.

Heating, ventilating and cooling buildings cause emissions. The materials we use cause emissions when we ship them long distances, or use chemical reactions and heat to create them. We have the technology and tools to calculate this more accurately than ever (and reduce it). However, few building projects actually do and even fewer make that information transparent.

BC: What’s a promising development you think should be adopted more broadly?

KL: Seagrasses like eelgrass can insulate buildings similarly to mineral wool, and can absorb CO2. We have used eelgrass as an insulation material in the US, Denmark, Germany, and the Netherlands – to just name a few countries, in the past. Rockefeller Center was insulated with eelgrass.

However new research shows we don’t know the full impact or benefit of insulating with natural materials (whether biobased, or wood, 0r seagrass).