SEAWEED ARCHITECTURE Eelgrass as a Construction Material Kathryn Larsen
Seaweed Architecture - Eelgrass as a Construction Material l B.Sc Architectural Technology and Construction Management l Copenhagen School of Design and Technology (KEA)
Specialization Report Title : Seaweed Architecture - Eelgrass as a Construction Material Program: B.Sc Architectural Technology and Construction Management School: Copenhagen School of Design and Technology (KEA) Date: 12 October 2018 Supervisor: Anke Pasold Characters (incl. spaces): 66077 All photos, sketches and images are done by the author, unless otherwise stated. The photos of The Modern Seaweed House are reprinted with permission of Søren Nielsen, and are credited to photographer Helen Høyer. The photos of Studio Seagrass’ products and installations are reprinted with permission of Tobias Øhrstrøm. I hereby confirm that I have carried out this dissertation report without any unrightfully help.
Seaweed Architecture - Eelgrass as a Construction Material l B.Sc Architectural Technology and Construction Management l Copenhagen School of Design and Technology (KEA)
Author’s Note It is important to note that this project is something that has never happened before at KEA, and never with the BUILD line and would not exist without the support of many people along the way. I am incredibly grateful for the personal support of my supervisors at Material Design Lab: Anke Pasold and Mette Marko Hansen and their connections to so many resources including to Det Teknologisk Institut (who ethically supplied the eelgrass for the project), as well as Anders Haldin of MakerLab who gave advice about the panel structure and let me work in the workshop around my work hours at Vilhelm Lauritzen Architects. Their enthusiasm and belief in me encouraged me to push the boundaries beyond what I could have ever dreamed was possible from studying at KEA. To my interviewees Kirstin Lynge, Tobias Øhrstrøm, and Søren Nielsen: many thanks for taking the time out of your busy schedules to meet or message me. Further thanks goes to Claudio Testa, head of program for approving the connection to the KEA BUILD line, along with Dan Korsgaard of Campus Service for helping to financially support the project and approving the structure. I am also full of gratitude for my husband Lucas Larsen who served as my assistant, helping me thatch the 54 sketch models over the course of two days and who helped me brainstorm different methods for thatching the larger panels. Finally, a huge thanks goes to Katrine Kringsholm-Eriksen and Sidsel Hemmer Rolighed of Vilhelm Lauritzen Architects for allowing me to adjust my work schedule during my internship to work on this project and meet with my supervisors during regular work hours.
Seaweed Architecture - Eelgrass as a Construction Material l B.Sc Architectural Technology and Construction Management l Copenhagen School of Design and Technology (KEA)
Abstract This is a dissertation about eelgrass in the Danish building industry, and the potential world-wide applications of this material. The aim of the report is to explore and demonstrate these applications, including eelgrass’ insulating and fire-retardant properties, as well as its architectonic value as material. Included is an original research project into creating prefabricated eelgrass-thatch panels with a wooden substructure. These panels will be displayed on the roof terrace of Guldbergsgade 29N on a four-sided installation, to study the effects of weather on them. The installation will continue for a year. This dissertation starts by examining eelgrass, its material properties, and environmental challenges before focusing on historical and modern case studies in Denmark. This focus on Denmark is due to the fact that there is a strong existing precedent in using this material compared to other countries. Included in these case studies is original research in the form of interviewing Søren Nielsen from Vandkunsten about Det Moderne Tanghus, Kirstin Lynge about Zostera Insulation and the history of seaweed thatching on Læsø, and Tobias Øhrstrøm from Studio Seagrass ApS.
Keywords : Eelgrass, Seaweed, Seagrass, Natural Insulation, Thatch, Thatching, Prefabrication
Glossary Seaweed / Tang . Multi-cellular algae with little to no vascular tissue (myfwc.com). Eelgrass often referred to in this paper as seaweed, however it is technically a seagrass. This is because the Danish word for seaweed is often used to refer to Eelgrass Seagrass / Søgræs . Vascular sea plants that have their own roots, stems, leaves and flowers (myfwc.com) Eelgrass / Ålegræs . The most common seagrass in the UK and in Scandinavia, it grows circumglobally in the Northern hemisphere (IUCN, 2018) Zostera Marina L. The scientific name for eelgrass (IUCN, 2018) The Seaweed Bank / Tangbanken. A seaweed bank established on Læsø to help preserve eelgrass for future renovation projects. The Modern Seaweed House / Det Moderne Tanghus A building project established by Vandkunsten and Realdania to experiment with using eelgrass in an experimental way
Table of Contents 1. Introduction.....................................................................................................6 1.1 Background........................................................................................7 1.2 Reason for Topic Choice.........................................................7 1.3 Problem Statement....................................................................8 1.4 Delimitation........................................................................................8 1.5 Research Method..........................................................................9 2. Eelgrass.................................................................................................................10 2.1 An Overview of Eelgrass.........................................................11 2.2 Eelgrass as Waste vs. Material...........................................13 2.3 Eelgrass’ Properties.....................................................................13 2.3.1 Fire Resistance..................................................................13 2.3.2 Insulation................................................................................15 2.3.3 Water Resistance............................................................17 2.3.4 Carbon Neutrality...........................................................17 2.3.5 Acoustics.................................................................................18 2.3.6 Fertilizer...................................................................................18 2.3.7 Rot and Mold Resistance.......................................19 2.4 Conclusion..........................................................................................19 3. The Seaweed Houses on Læsø....................................................20 3.1 The Traditional Thatching Method..............................21 3.2 The Updated Thatching Technique...........................22 3.3 Preservation Efforts......................................................................23 3.4 The Seaweed Harvest...............................................................25 3.5 Conclusion...........................................................................................26
4. Modern Applications of Eelgrass................................................27 4.1 Det Moderne Tanghus...........................................................28 4.2 Vankunsten’s Use of Eelgrass............................................29 4.3 Studio Seagrass..............................................................................31 4.4 Tobias Øhrstrøm’s Master Thesis....................................31 4.5 Studio Seagrass’ Experiments..........................................33 4.6. Zostera’s Insulation.....................................................................35 5. Eelgrass Thatch Reimagined..........................................................37 5.1 First Test Models and Methods.......................................39 5.2 Thatching Method with Different Binders..........40 5.3 Building the Larger Panels.................................................42 5.4 Installing Outside.........................................................................43 5.5 Conclusion Based on Present Data...........................44 6. Conclusion.......................................................................................................45 7. Appendix...........................................................................................................48 7.1 Interview with Søren Nielsen...........................................49 7.2 Interview with Tobias Øhrstrøm....................................50 7.3 Interview with Kirsten Lynge............................................52 7.4 Table 1...................................................................................................54 8. References and Works Cited.........................................................55
1.2 Reason for Topic Choice
This year, Denmark had the driest summer on record, with the earliest heat wave in 145 years due to the effects of global climate change (Brandt, 2018).
Seaweed, although seemingly an unconventional material choice in construction, has a large potential for the building industry. Neptune balls, or Posidonia oceanica, have already been explored as a solution for insulation (EcoChunk, 2013). When compressed and mixed with binders, the seaweed transforms into a sustainable replacement for wood panels or OSB (PHEE, 2018). This dissertation will focus on a type of seagrass called eelgrass. Although eelgrass grows globally, there is not much research available on its application towards construction.
As global climate change becomes more apparent, new solutions must arise to combat these issues. The UK Building Green Council states that one of the large contributors of pollution and waste is the building industry, which uses 400 million tons of materials a year. Many of these material choices by the building industry negatively affect the environment: construction blog BIMhow believes that 23% of air pollution, 50% of climate change, 40% of drinking water pollution and 50% of waste comes from the building industry alone (initiafy, 2016).
Much of the research that is available exists in Danish, due to the historical use of the seagrass as a roofing material on the island of Læsø (VisitLæsø, 2018). This dissertation attempts to translate this existing research and cultural context of its use for professionals across the globe, and compile different examples of construction solutions to prove the feasibility of eelgrass as a building material, as well as weigh the benefits and downsides of using it. It is the author’s hope that this dissertation and the experimentation in it can inspire architects and construction managers around the world to choose eelgrass as a sustainable solution and further develop research and products for use in the industry.
1.3 Problem Question
What are the benefits and downsides to eelgrass as a construction material?
This research paper focuses mainly on Denmark, with supplementary resources from the UK and the US. It also primarily focuses on eelgrass instead of other seaweeds or seagrasses, however, they may be briefly mentioned to provide context.
Eelgrassâ€™ beneficial properties, including non-toxicity, carbon neutrality, natural fire and water resistance, in addition to its cultural connection and value to Denmark make it a strong contender for future sustainable construction and experimental architecture in the Danish building industry, creating solutions that can be replicated globally, where eelgrass grows locally.
Although eelgrass grows globally, it has an extensive cultural link to architecture in Denmark through the seaweed houses of LĂŚsĂ¸, and Danish architecture firms have used this historical precedent to experiment with it.
However, there are potential issues with supply-and-demand due to the shrinking population of eelgrass, and the lack of a demand for products.
This paper is limited to mainly qualitative data through the use of secondary sources, observations and interviews, although some quantitative data is included with the primary source experiment and installation.
Since only dead eelgrass is used after washing up on shore, its use does not hurt the existing seagrass meadows, and there are ways to farm and harvest it without hurting the seabed.
Due to time constraints, on hand-in, the paper will only include a brief conclusion thus far on the affects of the weather on the installation, which will continue for six to nine months after hand-in.
Should a demand in Denmark exist for eelgrass products, there should be a sufficient supply.
1.5 Research Method Many of the resources gathered are secondary source Danish-language books, articles, papers and text that have been translated, as well as English-language patents on similar applications of eelgrass and seaweed. Several research papers are also cited due to their experimentation on eelgrass, which formed the basis for the primary research of the paper. The primary research for this paper includes interviews of both Studio Seagrass ApS and of Vandkunsten, who have extensively experimented with eelgrass, the former basing their studio on material experimentation relating to eelgrass. There is also an interview from Kirstin Lynge, founder of the company Zostera. Kirstin’s father is Henning Johansen, an eelgrass master thatcher who works on conserving the seaweed houses on Læsø, and she has also learned how to thatch under him. Zostera, in partnership with Advance Nonwoven, has created an eelgrass insulation product that is certified with Cradle to Cradle. Further included in this primary research is a longterm experiment and installation of pre-fabricated eelgrass thatch panels, built by the author with the guidance and financial assistance of Material Design Lab and Dan Korsgaard of KEA Campus Service. 9
The eelgrass for the installation was ethically sourced and provided by Det Teknologisk Institut, and the existing material research from Vandkunsten and Tobias Øhrstrøm of Studio Seagrass ApS was used as a starting point in the creation of these thatch panels. These thatch panels were created to capture the architectonic features of the seaweed houses on Læsø, while providing an experimental construction solution that is easier to install than traditional seaweed thatch-
2.1 An Overview of Eelgrass Eelgrass, also known scientifically as Zostera marina L., is a type of seagrass that grows globally (IUCN, 2018). It is rated as “Least Concern” on the IUCN Red List, a source for guiding conservationists on different species. However, the IUCN also notes that there are regions of large-scale decline, with a global decline of 1.4% per year, and that there have been ongoing restoration efforts in both Europe and North America to replant eelgrass (IUCN, 2018). These issues with decline have heavily affected the eelgrass population in Denmark, so although it is not categorized as endangered, it is not an infinite resource. In Denmark, a large-scale research project called Novagrass focuses on the replanting of eelgrass in the Limfjord and Vejle fjord (Novagrass, 2013). In 1900, eelgrass covered over one-seventh of coastal waters in Denmark. A fungal disease that also affected eelgrass populations across Europe and North America wiped out approximately 90% of the eelgrass in Denmark in the 1930s (Novagrass, 2013).
The seagrass meadows have never truly recovered from this wasting disease, and although eelgrass still washes up on the shores of Denmark, projects like Novagrass are fighting hard against the global decline. They develop mechanized eelgrass seed harvesters that can replant without overly-impacting the seabed, and monitor the planted eelgrass (Novagrass, 2013). Replanting, however, is a laborious process and is often unsuccessful. Previous efforts included attempting to reduce the nutrient-loads from land, which also was relatively unsuccessful (Novagrass, 2013). Excess runoff of nitrates and phosphates can create algae blooms, which prevent light from reaching the eelgrass meadows (Novagrass, 2013). One of the largest causes of nutrient pollution is agricultural-based, where run-off from manure or fertilizer in fields adds large levels of phosphates and nitrates to nearby water sources (EPA, 2018). According to a 2016 article, Denmark has successfully reduced their phosphate emissions by 50% and nitrate emissions by 90% since laws were passed in 1986 regulating farmers’ use of fertilizers (Fluence, 2016).
On the surface this seems like good news for the marine environment, however the reason why reducing the nutrient-loads from lands has failed to re-establish the eelgrass population is because that previous nutrient-loads have fundamentally changed the conditions of the seabed, making it difficult for new seedlings to flourish (Novagrass, 2013). However, Novagrass has created a way to farm the eelgrass, so that it can be harvested once a month, without damaging the seabed or the eelgrass plants themselves (Ă˜hrstrĂ¸m, 2018). This means that if there was a large enough demand for eelgrass products to outpace the amount of eelgrass regularly washed up, more could be sustainably farmed and harvested.
2.2 Eelgrass as Waste vs. Material
2.3 Eelgrass’ Properties
At the moment in Denmark, excess eelgrass is seen as waste, with the exception of three seaweed farmers on Møn and Bogø. Køge, Greve, and Solerød municipality all clean up 22,000 tons of eelgrass yearly, which is then discarded (Wittchen, Zibrantsen, Knudsen, Linnet and Devantier, 2018).
Eelgrass has many properties that are beneficial towards its use in construction, some of which have been well documented over time, and others that are more theoretical.
If the eelgrass is not properly harvested for use, it often becomes contaminated with microalgae, which causes the seaweed to rot (Nielsen, 2018). Too much eelgrass left on the beaches to decay can also cause nutrient loading, and further pollute the waterways.
The fire resistance of eelgrass stems from the salt impregnated in the seagrass, according to the Natural Homes organization (2013). The Colorado State Forest Service corroborates this, as they state that there is a correlation between plants adapted to saltier conditions and their fire resistance (Dennis, 1999).
If eelgrass is to be used as a material, it must be properly processed. Within twenty-four hours of harvesting the seaweed, it must be brought to a field. It is rained on and dried over the course of two weeks to two months (Wittchen, Zibrantsen, Knudsen, Linnet and Devantier, 2018). This removes the microalgae from the seaweed, and prevents it from rotting. The seaweed is now usable as a material. Thus, eelgrass as a building material could benefit the construction industry and local ecology, as well as serve as an extra revenue source to municipalities. 13
2.3.1 Fire Resistance
There are a few experiments that demonstrate eelgrass’ fire resistance. One experiment in Denmark by TV2 tested different constructions with different alternative insulation choices in between, and set them on fire. After thirty minutes, the fire was put out, and after forty minutes, the constructions were doused in water. The eelgrass construction consisted of 2x13 millimeters of Danogips Plank (also known as gypsum), with eelgrass in between.
Although the thickness of eelgrass was not specified, it was noted to be a “lawful construction”, which means it passed with the building regulations at the time of the experiment. After twenty-five minutes, the gypsum had burned through to the eelgrass. The eelgrass was slowly beginning to glow when the fire was extinguished, but there was very minimal damage to the supporting structure of the construction (Dollerup and Skov, 2004). Another experiment, although informal, by student Anna Plawecka in her undergraduate thesis, showed that the loose eelgrass catches fire quickly, but burns very slowly, and an eelgrass insulation product from Advance Nonwoven and Zostera is even more fire resistant (2015). How the eelgrass is processed appears to have some affect on the fire resistance, as the insulation product Plawecka tested consisted of shredded and milled eelgrass mixed with some binder (2015). This may be because shredding the eelgrass increases the surface area and density, meaning that a potential fire is exposed to a greater concentration of eelgrass.
Although this fire rating is not very good, this confirms the fireproof properties of the eelgrass, since the product only consists of a small amount of binder and eelgrass (Øhrstrøm, 2018). It also shows that eelgrass can meet industry standards towards fire resistance. According to Studio Seagrass founder Tobias Øhrstrom, the type of binder used when processing eelgrass is what impacts its strength of fire resistance (2018). In fact, the eelgrass plates made by Studio Seagrass, with a concentration of five-to-ten percent of natural binders, have a fire rating of B (Øhrstrøm, 2018). The eelgrass plates also contain large layers of eelgrass, compressed into shape. One kilogram of eelgrass fits into one twenty-by-twenty centimeter panel (Øhrstrøm, 2018). Just as shredding and milling increases the concentration of eelgrass in Zostera’s insulation, the compression in these panels increases the density of eelgrass per square meter. This amplifies the fire resistant properties, and results in greater fire resistance than loose, unprocessed eelgrass.
On the Cradle to Cradle website, they state that Zostera’s eelgrass insulation product has a “natural” fire resistance class of E (Cradle to Cradle, 2018). 14
2.3.2 Insulation As briefly discussed in the fire resistance section, there is currently an eelgrass insulation batt on the market that was developed, in partnership, by Advance Nonwoven with what is now known as Zostera, in 2014. Zostera is a business founded by Læsø seaweed thatcher and conservationist Henning Johansson’s daughter Kirstin Lynge. She is also a traditional seaweed thatcher from Læsø. (Zostera 2018).
Eelgrass was regularly used as an insulation material in Denmark as well.
Zostera’s eelgrass batts have a lambda value of 0.037W/mK (2018). However, long before this product came onto the market, eelgrass was used historically an insulation material.
The price-point comparison for the seaweed and the amount needed to insulate as space are very similar to rockwool in this book, so it appears that it was a common choice.
One of the earliest evidences for its use as a product was in the US, where a product called “Cabot’s Quilt” was patented in 1891. This early solution consisted of eelgrass that was sewn between two layers of cardboard, to make insulation rolls (Cabot, 1923). However, according to the product booklet for Cabot’s Quilt in 1923, older houses in New England dating back to the 17th and 18th century had their walls stuffed with loose eelgrass, inspiring this product. The booklet claims that the eelgrass was perfectly preserved, to the point of showing a a bottle containing eelgrass that was from the 288-year-old house (Cabot, 1923).
This is furthered by the fact that the book casually uses seaweed batts as an example, when talking about varying insulation thicknesses in rooms (Københavns Teknisk Forlag, 1950).
A material pricebook from the 1950s for insulation that was founded by Copenhagen’s Technical Publishers shows a price comparison for seaweed batts, sewn in between cardboard, much like the Cabot’s Quilt product (Københavns Teknisk Forlag, 1950).
If it was an obscure insulation material at the time, it is unlikely that it would have been used in these sorts of examples in the book, which would have served as a guide for construction managers in the day.
Zostera, the company that has produced modern eelgrass batts with Advance Nonwoven, states on their website that during this time period, there was a seaweed exporting business called “Kalvehave Tangkompagni”. From 1917 to 1959, this seaweed company bought eelgrass from farmers on Zealand, Møn and Bogø. The eelgrass would then be turned into insulation products, or used to stuff mattresses (Zostera 2018). The most likely reason for the decline of the seaweed batts, and the reason why they are not commonly used today, is because of the wasting disease. If there was not enough healthy seagrass to supply the industry, prices for it would have increased, and the construction industry would have switched to rockwool or another affordable insulation material with a comparable lambda value.
Vandkunsten, a Danish architecture firm, used eelgrass as insulation in their timber-framed house, Det Moderne Tanghus, or The Modern Seaweed House, by measuring out the proper amount of eelgrass needed for the correct u-value, and pressing it into the prefabricated wall cavities (Nielsen, Klebak, and Søndermark, 2013). Søren Nielsen, who headed the project, believes that it is possible to use loose eelgrass as insulation in masonry buildings as well, as long the construction is properly ventilated (Nielsen, 2018). Thus, Eelgrass is a suitable alternative choice for insulation, especially for timber construction, and complies with building industry standards.
The fact that eelgrass was used regularly in many different places as an insulation material from the 17th century to the 20th century, means that it had to have been a good insulator. In fact, according to Jørgen Søndermark from RealDania Byg, it is a suitable insulation material because it has a lambda value of approximately 0.038W/mK, and 100mm of modern rockwool is equivalent to 120mm of unprocessed eelgrass (2013).
Seaweed Architecture - Eelgrass as a Construction Material l B.Sc Architectural Technology and Construction Management l Copenhagen School of Design and Technology (KE
2.3.3 Water Resistance
2.3.4 Carbon Neutrality
Eelgrass is not very water resistant at first. It acts like a sponge, and can absorb up to ten times its weight in water (Øhrstrøm, 2018). When thatched traditionally however, on Læsø, after about a year the natural binders released by the seaweed glue the roof thatch together.
Embodied carbon in building materials refers to the energy used to create these materials. Highly processed materials that have been transported long distances have a higher embodied carbon value. Choosing materials with low embodied carbon means reducing the amount of carbon dioxide emissions that the building industry creates (Lane, 2010).
The roof turns silver, solidifies and becomes completely water resistant (Miles, 2008). The roof is often a meter thick or more, however, so the construction is usually watertight before this process occurs (Jensen, 2012). This means that if eelgrass is used in a construction in a smaller thickness or is not mixed with a waterproofing binder, a membrane may be necessary.
Eelgrass is carbon neutral, and when used in the Modern Seaweed House, created a carbon negative footprint of 8,500kg of CO2 (Mikkelsen, 2013). This energy rating means, that although the Seaweed House was built in 2013, it is energy compliant with 2020 standards. This was because the materials utilized had such low embodied carbon. It is also because eelgrass binds carbon dioxide, and can be harvested and processed locally without using a lot of energy or transportation. (Nielsen, Klebak, and Søndermark, 2013). In order to best utilize eelgrass’ carbon neutrality, it should be used locally and harvested locally instead of shipped far distances.
Considering that eelgrass grows globally, it is a good material choice for sustainability and can help combat the carbon footprint of the global building industry.
Some sources on the acoustic properties of eelgrass are mostly theoretical. An old ad for Cabot’s Quilt touts the insulation product as a “sound deadener” (1923). Furthermore, Jørgen Søndermark from Realdania Byg believes that the Modern Seaweed House has demonstrated that eelgrass “has remarkable acoustic properties” (Frearson, 2013).
Eelgrass has a history of being used as a fertilizer as well, for certain plants. This can also be seen in the fact that it can add to nutritient-loading after washing up on shore.
Tests done by Delta however, confirm the acoustic properties of the Zostera eelgrass batts. Eighty centimeters of the seaweed batt was acoustically tested, along with different thicknesses of mineral wool as a control. The batt has a harder side, and a softer side. These differing sides both have different acoustical performances. The softer side performs best with noises between 630-2000 Hertz, ultimately reaching a sound absorbtion coefficient of 0,99. The harder, more compact side performs best between 315-630 Hertz, and again after 1250 - 2000 Hertz, reaching a maximum sound coefficient of 0,90. Both sides of the seaweed matt had comparable sound absorbtion coefficient results to 80 millimeters of mineral wool (Advance Nonwoven, 2016). Since the eelgrass batt is mainly composed of eelgrass, and only a minimal amount of binder, the sound insulating performance of the batt can be attributed to the eelgrass itself.
Its salt concentration, however, means that it is not suitable for every type of plant (Øhrstrom, 2015). On Læsø, the seaweed houses support up to thirty-nine different plant species on their roofs in the summer (Jensen, 2012). Part of this is because the climate has changed on Læsø after the replanting of the forests, and there is less salt in the air. This encourages more plant growth on the roofs (Miles, 2008). However, this is not necessarily good for eelgrass’ purpose as a construction material, especially when used as an external roof or façade material. Although the plants give a beautiful aesthetic to the seaweed roofs, they also eat at the seaweed over time as they die and rot in the roof, meaning that the roof will have to be repaired and re-thatched more often.
2.3.7 Rot and Mold Resistance
Just like eelgrass’s acoustic properties are mostly based in theories, so are eelgrass’ rot and mold resistance. As mentioned in the fertilizer section, the biggest challenge regarding to rot is that other plants take root in the seaweed roofs, and eventually die and decompose. However, the seaweed roof itself does not rot. This is likely because of the salt content of the eelgrass, as salt acts as a natural preservative. The Cabot’s Quilt advertisement, again, states that eelgrass “non-decaying” (1923). Their justification for this product claim is that, after hundreds of years, perfectly preserved eelgrass was found stuffed in the wall cavities of New England homes. Further proof exists in the longevity of the seaweed houses on Læsø, with roofs that last two hundred to three hundred years (Tangbank, 2018). If rot and mold were issues with these houses, it is unlikely these roofs would have lasted as long as they did.
2.4. Conclusion Eelgrass has many favorable characteristics as a potential building material, especially in regards to its carbon neutrality, insulation, and fire resistance. Like wood, it has a potential multipurpose use in a building: it can be used as insulation or externally as cladding. However, it is more sustainable than wood, especially harvested close to place of use, because removal of the dead eelgrass improves coastal water quality and prevents nutrient loading. It transforms a substance seen as waste into a useful product. The downside is that is not water resistance at first and depends on the type of construction to create water-resistance. Thus using construction solutions with a membrane may be a necessity, if the eelgrass is used externally. Care must also be taken, in regards to its ability to support plant life. Although this can be a desired aesthetic, it can increase the amount of maintenance needed. Eelgrass also appears to perform well as a sound-insulator. Its longevity as a material in insulation and roofing on Læsø are the best evidence for its rot and mold resistance. All together, it is a favorable building material.
3. The Seaweed Thatching on Læsø
Seaweed thatching began on Læsø, after the Vikings on the island ran out of timber due to deforestation. Straw thatching was not an option either, so the villagers turned to the sea. It was traditionally women’s work, and required the help of around forty people (VisitLæsø). This is where the term “washer woman” or vaskerpiger comes from, as it was the womens responsibility to twist the dried seaweed into large, tearshaped “vasker” with thin ends (Tangtag 2018). Two women usually handled each vask and the technique for twisting it likely came from spinning wool.
3.1 The Traditional Thatching Method The original thatching method began with the eelgrass itself. In autumn, during the seasonal storms, eelgrass would wash onshore in large amounts. It was gathered from the beach and spread on a field to be rained on and dried, for at least half a year.
Finally, the ridge of the roof would have turf applied to keep the eelgrass in place (Øhrstrom 2015).
Once spring came, the women would begin to process the eelgrass by twisting it into a rope. The end of the large teardrop-shaped seaweed rope, called the “gumlinger”, was loose, while the top of rope, the “vaskere”, was tightly coiled so it could be attatched to the wooden beams of the roof (Øhrstrom, 2015). The thicker and tighter these ropes, the more ideal, as they served as the foundation for the rest of the thatch. They were often two meters long in length, as well (Kaushik, 2018) Pine branches would be placed along the roof structure, and then more seaweed would be piled on top. A girl would dance on the roof, to compress down the eelgrass, and begin to release the natural binders of the seaweed.
At the six-month mark, more eelgrass would be added to fill in the roof gaps, and openings would be cut in the older eelgrass for windows and doors.
For good luck, before the roof was sealed, a calf’s head would be tossed in, or a cat. According to master thatcher Henning Johansen, it was important that the cat be alive (Miles, 2008). 21
The work did not end there though. Eventually, gravity would pull the eelgrass down the roof.
Finally, the roof would be ready. Over time, the eelgrass would continue to slide down and settle, and after a year, the roof would be watertight (Øhrstrom 2015). The final roofs were at least a meter thick, and this enabled people to stand on the roof. The ridge of the roof was so wide that it was possible to even bring a chair, and have a seat, while scanning the sea after a storm. Shipwrecks were an important source of income for villagers, since the driftwood and timber recovered could be salvaged and sold (VisitLæsø, 2018).
The traditional method of seaweed thatching was a highly labor-intensive process that often required the work of the whole village (VisitLæsø, 2018).
3.2. The Updated Thatching Technique
As a result, it is not necessarily a good building technique to replicate in modern construction. The resulting construction is also extremely heavy, with over three hundred kilograms of eelgrass used (Kaushik, 2018).
Although thatching the roofs used to be primarily women’s work, these days it is headed by seaweed thatcher Henning Johansen, who, with his crew, heads most of the roof thatching and conservation on Læsø. Instead of forty people, now, only four to seven people are required to build a roof.
Restoring a seaweed house can also take up to eighty tons of eelgrass (Lynge, 2018). This also means that the underlying structure of a house must be very strong, to resist warping.
A machine with large electric spindle on one end and a drill on the other helps speed up the process of making appropriate seaweed ropes, which is now about twice as fast as the traditional manual process.
However, as a traditional and vernacular building method, it is extremely valuable. The seaweed houses are tied to the cultural history of Læsø, and by extension, Denmark.
After the seaweed vasks have been placed on the rafters, a crane drops more eelgrass on top of the roof, where the crew spreads it out. Soon after the roof is completed, the windows and doors are cut out with a chainsaw. The roof settles with gravity, and after six months, if seaweed has slid down, the roof is trimmed (Lynge, 2018). This gives an idea of the level of maintenance required from this building method. After a year, the roof is solid, and requires little maintence apart from removing dead plants. The process itself has not changed that much from the old method, but has been enhanced by new technology. 22
3.3 Preservation Efforts Originally, every house on Læsø but the churches had a seaweed roof, and as of 2008 there were only twenty (Miles, 2008). Just as the seaweed insulation trade in Denmark suffered from the eelgrass wasting disease, so did the seaweed roofs on Læsø. It became easier and easier to replace the seaweed roofs with straw thatch or modern materials instead of eelgrass (Tangtag, 2018). There was simply not enough eelgrass to continue making the proper repairs. By 1962, many of the original seaweed roofs were in bad shape. When King Frederick IX visited Læsø then, he advised that they take care of the roofs, and do what they could to preserve them (Jensen, 2014). However, it would take many decades until the roofs could be replaced (Tangtag, 2018). The original thatching technique was almost lost, had it not been for thatcher Henning Johansen, in 2008. Henning had been replacing the seaweed roofs on the island with straw thatch, and from dismantling them, learned how they had originally been constructed. From this, he began restoration work on the roofs, and learned as he went, to refine his technique (Lynge, 2018). 23
Johansen founded what would become known as the Seaweed Triumvirate, along with Poul “Salt” Christensen, and Marcelle Meier. Christensen was Johansen’s neighbor, and had received millions of kroner in funding towards the Læsø Salworks. Meier was an Arhus architect. They banded together to try and save the seaweed houses (Jensen, 2014) In 2008, they began their so-called “pilot project”. They sought money from Realdania to restore the seaweed roof of Kjeld Hus Barn, which was actualized in September and October of 2008. According to Johansen, they received three tons of seaweed from Bogø, which was terrible quality. Its quality meant that they could not make uniform vasks, and they needed the seller to deliver instead a new harvest from the year. Amongst all else, they learned that when seaweed thatching, not all seaweed was equal (Jensen, 2014). The following year, they gave Hedvigs Hus, owned by Læsø Museum, a new gable and part of the roof restored.
2011 was the big year for seaweed, because the Cultural Agency of Denmark bought Andrines Hus, which was almost in ruins. The home was completely renovated, and afterwards, was given a new seaweed roof from start to finish. Another gable on Hedvigs Hus was restored to seaweed from roof panels, and they also completely restored the seaweed roof at Frilandsmuseet, or the Danish Open Air museum (Jensen, 2014). Since 2012, funds have been allocated from the AP Møller Foundation, The Agency for Culture and Palaces, the Augustinus Foundation and Realdania to help preserve and restore the seaweed houses. However, the center for Building Preservation in Raadvad has estimated that restoring all thirty-six homes on the island with seaweed roofs will cost approximately ninety million Danish kroner. This is because the houses, in addition to the roofs, also require repairs (Tangtag, 2018). In the autumn of 2010, the Seaweed Triumvirate established The Seaweed Bank, or Tangbanken. According to Poul Christensen, the name is because good eelgrass has as much value as gold for Læsø’s old farms, so it was natural to call the seaweed storage a seaweed bank (Jensen, 2012).
The seaweed bank aimed to buy seaweed from farmers on Møn and Bogø, and store them, to use for future repairs on the island. The supply of eelgrass fluctates from year to year, so this was the motivation to create the bank. If there was a bad harvest one year, there would still be enough to continue preservation work. The goal is to store one hundred tons of eelgrass from Møn and Bogø in the bank, to only be used in an emergency (Tangtag, 2018). A 2012 book, Tængemand og Vaskerepiger, proclaimed that 2011 was the busiest year to date for the bank, with thirty-five tons of eelgrass delivered (Jensen 2012). Restoring an eelgrass roof can take thirty to fifty tons of eelgrass, so this is why the goal for the bank is to always have one hundred tons at the ready. The bank is a nonprofit organization, and is driven by unpaid and volunteer work (Tangtag, 2018) The seaweed that was purchased originally by the Læsø Museum from Bogø, was shipped in loosely pressed balls, with circa two-and-a-half tons per truckload. However, the quality of the seaweed can be difficult to determine- although there is a quality assessment of suppliers on Bogø and Møn, there is a large difference between the final quality that can be used on the roofs. 24
The Seaweed Bank has learned that there is an amount that is not suitable for roofing, neither for turning into a “vask” nor for lying on top, with each delivery. However they cannot precisely determine how much of each delivery is unusable. The basis of the seaweed bank are loans, so there needs to be enough money generated over the next few years to secure the investment. At the moment, the return has been estimated to be 5DKK per kilogram (Tangtag, 2018).
3.4 The Seaweed Harvest As stated previously, originally it was the women on Læsø that gathered the seaweed as it washed up on shore. When the seaweed industry became lucrative under Kalvehave Tangkompagni, the rise of seaweed farming became an equally profitable industry. Farmers on Møn, Zealand, and Bogø harvested over five hundred tons of eelgrass yearly, at the peak (Zostera, 2018). However, the industry died out around the 1960s, likely due to the eelgrass wasting disease causing the prices to rise, and the building industry turning to cheaper insulating materials. 25
When Henning Johansen looked at restoring his first house, he contacted the families of these farmers on Møn and Bogø. Their children remembered gathering seaweed on the beaches, and the industry of seaweed farming restarted (Lynge, 2018). Both Kirstin Lynge and Tobias Øhrstrøm, who have founded their businesses based on eelgrass products and experimentation, agree that there is no issue with potential eelgrass supply in Denmark. At the moment, there are only three seaweed farmers in Denmark, and from two kilometers of coast, they can provide four hundred tons of seaweed yearly. The largest issue is cost, and the fact that other parts of Denmark do not see the seaweed as a valuable material. If more people began farming seaweed for use in seaweed roofing or insulation, then the price could lower and the subsequent products could become more price-competitive with other building materials. Currently, eelgrass costs almost 150DKK per square meter for one hundred millimeters of insulation (Lynge, 2018).
3.5 Conclusion The Seaweed Houses on LĂŚsĂ¸ shows how resilient of a material eelgrass is long-term, with roofs lasting hundreds of years. The construction and thatching method is valuable in its vernacular and cultural contribution, however it is not necessarily ideal to replicate in modern construction due to the time to construct, and the amount of labor required, as well as the large amount of eelgrass needed. The large amount required inspired an initiative to create a seaweed bank on the island to provide enough eelgrass, but this could be difficult to replicate in other countries. This means that as a construction solution it can be very expensive, and not necessarily feasible. Overall, however, it is an extremely strong architectural precedent, and worth conserving and protecting. At the moment, there are only three seaweed farmers in Denmark. Although there are no issues with the potential supply of eelgrass, it is not seen as a valuable resource by other municipalities. If this changes, it could be the rebirth of the seaweed farming industry in Denmark.
4. Modern Applications of Eelgrass
The seaweed houses on Læsø have inspired a variety of experimentations and interpretations from ontemporary architects in recent years in Denmark, and an insulation product that is, at present, the only insulation to be certified cradle-to-cradle gold.
Photograph by Helen Høyer
4.1 Det Moderne Tanghus In 2012, after restoring the seaweed roof to the 150-year-old Kaline’s Hus on Læsø, Realdania Byg launched an architecture competition. The old house lay next to a completely modern summerhouse, with only a small parcel of land in between. Realdania bought the parcel of land with the intent of building a new summerhouse there that could properly transition tectonically between the two. The aim was to have architects use eelgrass, but in an innovative way, with a home that could be designed and built in under a year. Vandkunsten rose to the challenge, incorporating prefabrication to speed up the building process (Nielsen, Klebak, and Søndermark, 2013). The house’s design came together quickly, as it was not intended to be a social experiment, but rather a material experiment.
As it took a village to thatch the seaweed homes, it equally took many hands for the Modern Seaweed House to come to life. The eelgrass for the home came from a farmer in Bogø, who harvested the seaweed locally, and allowed it to dry on his meadow for fourteen days. It was pressed into bales, which were then sent to the prefabrication factory, Green House. The seaweed elements were the largest challenge for the factory workers, as the interior wall and ceiling elements could not be screwed into place as normal. Instead they had to be snapped into place. These small details meant that that it was difficult to know how long the prefabrication process would take, and it required highly skilled craftsmen. Using eelgrass to insulate the walls was also challenging, because the loose, dried seagrass had to be pressed into the walls (Nielsen, Klebak, and Søndermark, 2013).
The design itself was traditionally based on a classic Danish summerhouse design, with a large communal center area and several private rooms. Keeping the design relatively simple allowed for the functional purpose of the eelgrass to take center stage (Realdania Byg, 2013). Photograph by Helen Høyer
Praktisk Service hand-knitted the wool netting, or “stockings” for the eelgrass for the facade.
Each six meter long netting took three hours of handiwork. The façade and roof required 1,100 meters of stockings in total. They were knitted from brown wool from Møn, a color that matched the eelgrass (Nielsen, Klebak, and Søndermark, 2013). While the Modern Eelgrass House functions well as a material study, this kind of eelgrass application was not necessarily realistic or practical for the building market. There was a lot of labor involved, requiring highly skilled craftsmen and knitters. Perhaps this is one of the reasons why despite its international acclaim, it has not been attempted to be replicated in other places. The knitting abilities and labor required, combined with the level of skill for the prefabrication required would not be easy to replicate.
4.2 Vandkunsten’s Use of Eelgrass
Vandkunsten embraced the use and the history of eelgrass entirely in their design. The soft-netted pillows cladding the building are an ode to the use of eelgrass as mattress stuffing, as well as the roof interior, which is clad in cloth. The timber constructed walls, floors and ceilings, which were prefabricated, were stuffed with a measured amount of eelgrass to provide the proper u-value. All in all, eelgrass was used in three ways: as insulation, as internal padding, and as a visible external façade (Nielsen, Klebak, and Søndermark, 2013). They tried multiple ways of experimenting with the eelgrass by twisting and braiding it, but ultimately chose to balance the unruly forms of the eelgrass with the form-binder of the wool rouse. They chose not to compress the eelgrass into geometric shapes, since they felt that it would disrespect the nature of the material.
Photograph by Helen Høyer
However, unfortunately, the Modern Seaweed House was not successful ultimately in its construction. The roof had to be replaced with a wooden roof, because the construction was not watertight enough. At the present there are no more seaweed pillows on the roof (Nielsen, 2018).
Combining the idea of prefabrication with the eelgrass was a revolutionary idea. This directly inspired the author to develop a prefabricated eelgrass thatch panel. Prefabrication can lower labor costs and reduce the amount of building time needed on site. Although Vandkunsten’s experiment paid homage to the eelgrass’ history and its use in an external building material, it also did not necessarily pay homage to the method of thatching. Encapsulating the eelgrass in a net, although an effective way to add order and “tame” the eelgrass, loses the original tectonic value of the thatch method. The eelgrass’ tectonic potential is lost, as it is simply captured and held in place. Eelgrass thatching, although a highly precise skill and technique, aesthetically is imprecise and organic. It is this imprecision that attracted the author to try and capture it in something that could be used in the building industry. Although ultimately, their solution failed, Vandkunsten succeeded in putting eelgrass and the Læsø seaweed houses on the map. The project was extremely well documented and received a lot of publicity in English as well as Danish, which lead to a greater awareness of eelgrass as a building material. Their experimentation directly influenced Tobias Øhrstrøm, founder of Studio Seagrass, as well as the author Photograph by Helen Høyer
4.3 Studio Seagrass Studio Seagrass is an architecture studio based in Frederiksberg, Copenhagen that experiments with eelgrass. They have received three years of funding from Statens Kunstfond to prototype and experiment with eelgrass’ potential (Fabrin and Øhrstrøm, 2018). They believe that although eelgrass as a roofing material is well known in Denmark, it is not the only option. Their studio is centered on different prototyped solutions of eelgrass for a variety of purposes, from interior design, to construction, and beyond. The studio is lead by the architects Tobias Øhrstrøm and Pi Fabrin (Fabrin and Øhrstrøm, 2018).
4.4 Tobias Øhrstrøm’s Master Thesis
One of Studio Seagrass’ founder, Tobias Øhrstrøm conducted an extensive amount of qualitative research on eelgrass for his master’s thesis, called BioConcretion. In his research, he tested several different methods of treating the eelgrass: compressing, interlocking, weaving, and binding (Øhrstrøm, 2015). Øhrstrøm mixed eelgrass with different natural binders, and in some cases, filers such as sawdust, and recorded his thoughts on it. These binders included agar-agar, a seaweed based binder, hide glue, gelatin, and casein glue. He preferred hide glue in a concentration of 50/50 for a strong, structural compound of eelgrass and binder, and noted that adding 0.5% of aluminum sulfate made the mixture waterproof (Øhrstrøm, 2015). Gelatin also made the eelgrass water resistant (Øhrstrøm, 2015). However, many of the binders were not very heat resistant, and Øhrstrøm noted that this could potentially cause issues for a façade (Øhrstrøm, 2015).
Photo by Studio Seagrass
Although Tobias’ research provided a good starting point towards experimentation with binders and eelgrass, he had only tested four and not specified the type of hide or gelatin glue he had used, as different binders from different animals hides or horns can have different bloom strengths. In general, the higher the bloom strength of a gel, the higher the melting and gelling point (Schrieber and Gareis, 53). If Øhrstrøm thus used binders with a low bloom number, this would have affected the heat resistance of the mixture. Furthermore, he had not specified the ratio of eelgrass-to-binder used in his experimentation with casein glue, agar-agar, or gelatin. As his thesis was for a Masters of Architecture, however, this lack of quantitative research was to be expected, as the focus of the thesis was on the historical, visual and tectonic performance of the eelgrass, and how to incorporate it into computational design. All this was taken into consideration when designing the eelgrass thatch panels (see 5. Eelgrass Thatch Reimagined), and there was an attempt to record carefully more quantitative information on each experimental sketch model, which can be seen in Table 1. Photograph by Tobias Øhrstrøm
4.5 Studio Seagrass’ Experiments
Studio Seagrass has many projects, some with clear construction applications. One kind, called “pillows”, has different shapes pressed into the eelgrass, reminiscent of padding. Tectonically, they are inspired by the soft, organic shapes that eelgrass makes when gathering on the beach. Another, called “folders” takes inspiration from the organic folds in cactuses and mussels. A final called “plates”, appears to be very similar to an OSB board (Fabrin and Øhrstrøm, 2015). In terms of design and construction, the plates appear to be extremely similar to an existing product for a prefabricated Posidonia oceanica board, which consists of a large amount of the seagrass mixed with binder and compressed under pressure (PHEE, 2018) At the moment, Studio Seagrass is working to have their “pillow” eelgrass panels produced on a larger scale in Jutland, and are working on a solution with Zostera to combine their plates with the insulation. The plates have many possibilities, mixed with different binders, such as soy and starch (Øhrstrøm, 2018). 33
FOLDER AND PILLOW
Photo by Studio Seagrass
The different binders can create different finishes to the panels. Some add a glossy finish, others a matte. There are even different color options: one plate is bleached, giving an aesthetic similar to wood fiber cement board. Øhrstrøm estimates that in the last two-and-a-half years, the studio has experimented with over twenty-five binders, well expanding beyond his original masters research (2018).
The largest challenge with these plates is moisture, since eelgrass is so absorbent. The binder needs to be strong enough to hold the plate together, should it come into contact with water. Another project by them called “Væve” or Weave explores the architectonic potential of the eelgrass further. The dry eelgrass is woven into smaller steel structures, creating different shapes and order to the lose material. These steel and eelgrass modules can then be attatched row-by-row to the wooden installation frame (Øhrstrøm, 2018). The eelgrass weaving is substantially different from the original thatching method, and the result is a construction that, while architectonically is reminiscent of the original seaweed houses, has a higher degree of order and neatness.
Photograph by Studio Seagrass
Photograph by Studio Seagrass
These projects in particular were used visually as a precedent for the prefabricated eelgrass thatch panels that were later developed. Overall, Studio Seagrass’ research and installations show many different applications and methods that can be achieved with eelgrass, and they successfully showcase the versatility of the material from an architectural perspective, as well as a functional perspective.
4.6 Zostera’s Insulation As previously mentioned in the sections on insulation and acoustics, Zostera has an eelgrass insulation product on the market. It performs as an insulator, and as a sound insulator comparably with mineral wool. It is the only insulation on the market that is cradle-to-cradle certified gold, and the only insulation on the market at the moment that is made from eelgrass. The insulation is solely made up of milled eelgrass, and a plastic binder. When making the insulation batt, the mixture is heated to 130 degrees Celsius, and no water is used, which reduces the amount of embodied carbon in the product. It is naturally fire resistance class E, as no chemicals or additives are added to the batt to make it fireproof. The eelgrass helps absorb carbon dioxide as well. One of the best benefits of the product is that it is completely recyclable. An old batt can be re-milled into a new batt (Lynge 2018). It is easy to handle, as it is itch-proof, and can manually be cut down to size without the need for gloves. It also works very well with moisture and can create a breathable construction (Øhrstrøm, 2018).
Photo by Studio Seagrass
When scientifically tested by the Danish Technological Institute over a period of seven days for harmful emissions, no known carcinogenic, endocrine disruptors, mutagenic, teratogenic, reproductive toxins or volatile compounds were detected in the applied measurements (Advance Nonwoven, 2017). This complies with Cradle-to-Cradle Product Standard emissions testing, and demonstrates that the product should not negatively affect inhabitants or indoor climate when used in a building. The benefits of using natural insulation is being tested right now in an SBI and Danish Technological Institute study, lasting from 2018 to 2019. This is because the 2020 building regulations have had a negative development: as the regulations have become stricter, the focus has moved away from sustainability, and instead towards circumventing the purpose of the building regulations. Loopholes and cheap shortcuts are chosen over using a more sustainable, yet possibly more expensive solution. Sustainability is more than just how many solar panels are placed on a roof; it is about choosing responsible materials and building with a lower carbon footprint. Eelgrass insulation is being tested, along with clear glass, in a classroom environment, to see how it impacts energy consumption and indoor climate.
The project ideally will demonstrate that using natural materials like eelgrass and clear glass in the windows can achieve greater sustainability, lower energy consumption, natural ventilation, and better space acoustics. Based on the results of this project, a new school will be built, utilizing sustainable materials (Energiforskning, 2018). The biggest downside to Zosteraâ€™s insulation is the price point at the moment, which is likely tied to the amount of eelgrass needed to produce it. For ten centimeters thickness of batt, there is five kilograms of eelgrass per square meter of product (Lynge, 2018). Another downside is the fact that it is only fire resistance class E. However, it is the first of its kind on the market, and the product is still very new. It paves the way for a new era of green construction solutions. The cost can be seen as an investment towards reducing the amount of carbon used in the building industry, and an investment in sustainability.
5. Eelgrass Thatch Reimagined
In order to demonstrate the usability of eelgrass as a construction material, prefabricated thatch panels were created. The idea for creating seaweed thatch panels came from Vandkunsten’s use of prefabrication, combined with the thatching method from Læsø. The goal was to create a product which could reduce the amount of labor required to thatch, while staying true to the original techtonics of the Seaweed Houses. Tobias Øhrstrøm’s research inspired the overall starting point: mixing eelgrass with natural binders, as well as the desired aesthetic of weaving and exploring differently spaced substructures . The process began first by establishing a technique for working with the eelgrass. Using either rehydrated eelgrass or eelgrass with natural binders, the resulting mixture was twisted into ropes. The next step was to progress to prototypes. Sketch models were made with the different mixtures to weave and loop the seaweed ropes around. After this stage, medium sized panels were made, and then two final large-scale panels. The results were installed on the roof of Guldbergsgade at KEA, in a year-long installation to test the affects of weathering.
At first, testing began only with rehydrated eelgrass, home-made casein glue, and bone glue. With these initial tests, there was a variety of concentration of different glue-to-eelgrass ratios, to figure out what the best concentration was for working. Too much glue would make the mixture difficult to work with, and compromise the eelgrass. Through working with these three mixtures, the overall desired concentration was refined. Upon first examination of the dry eelgrass, it crumbled, easily, whereas when wetted, it was stronger. Thus, the decision was made to rehydrate the eelgrass, and then add binder to it. To use the seaweed, it first had to be rehydrated. This was done by filling a large bowl with some water, and soaking the eelgrass in it for two to three minutes, after which the seagrass could be thatched as it was, or binder could be added. In the first experiment with binder, the casein glue was homemade using half a liter of skim milk and six tablespoons of vinegar over heat. The curdled mixture was strained and then added to the eelgrass. The second experiment with binder used bone glue, which had to be melted in a pan over heat, with water added. The consistency of the bone glue was too thick at first, which made it difficult to disperse evenly in the eelgrass. A thin consistency of the glue was ideal, and this was refined with the first bone glue sketch models.
5.1 First Test Models and Methods Initial tests used two parts of binder to one, a very large amount of binder. The large amount of binder made working with the eelgrass difficult. It was hard to twist and hard to maneuver. This was brought down to five parts of binder to one.
Next, using the two different binders, and the rehydrated eelgrass, sketch models were produced. Sketch models are small-scale architectural models, often devised to quickly produce ideas, and they are good for experimenting with different materials. There were two different typologies of sketch model created: a “loose” panel and a “woven” panel. The loose panel was based off the architectonics of the island of Læsø, with only horizontal substructure that the small ropes could be attatched to. However, unlike the thatch method on Læsø, the loose panel had vasks attatched on every rafter, instead of piling seaweed on top and using gravity to hold it in place. This meant that a thick thatch could be achieved, and that if the panel was transported, the seaweed would not slide off. The woven panel consisted of a gridded substructure where the ropes could be woven 39
through, creating a neater and more orderly appearance, inspired by Vandkunsten and Studio Seagrassâ€™ desire for order. However, despite the gridded substructure of the woven panel creating a neater thatch, the resulting thatch was still very organic and reminiscent of the original seaweed houses. Rabbit glue, bookbinding glue, hide gue, fish glue, agar-agar, and casein glue were then bought online, and in an assembly-line process, using the mixture concentration defined of five parts binder to one part eelgrass, three of each type of sketch model was made. In the earlier stages, individual small batches were made. In this stage, large amounts were made with up to a kilogram of rehydrated eelgrass used. The rabbit glue, bookbinding glue, and hide glue all were similar to bone glue, in that they had to be melted over heat, with water added to create a thin consistancy. This was then measured and distributed into the rehydrated eelgrass.
The Sketch Model Assembly Line
The fish glue came already rehydrated, so it was used at the consistency bought online. The agar-agar and casein glue both came in powder form, and were mixed in water before being brought to heat.
5.3 Thatching Method with Different Binders Working with rehydrated eelgrass alone proved to be extremely successful. Although traditionally thatched dry on LĂŚsĂ¸, the rehydrated eelgrass was strong and easier to manipulate than dry. The dry seaweed was easily crushed. Using just water, the strands of eelgrass did not stick to one another, however it did hold its shape in the rope well. After being attatched to the loose sketch panel, the ropes unraveled, however at the attatched end, they stayed firmly fastened to the structure. The mixture of homemade casein glue, when added to the eelgrass, allowed for the seaweed rope to be twisted tighter, but the strands stuck to one another as well, which made it tricky to maneuver into the right place on the structure. Also, the casein glue foamed when interacting with the eelgrass. The bone glue, hide glue, rabbit glue, and bookbinding glue all reacted relatively the same with the eelgrass mixture. They are all bone and hide-based glues, but with different bloom strengths and animal sources. All of them seemed to increase the brittleness of the eelgrass, as the rope began to snap more often, and the oily texture affected the strength of the eelgrass ropes twisted. 41
After drying, the brittleness of the eelgrass seemed even more apparent, as the eelgrass snapped easily under pressure. The eelgrass dried with a glossy texture, and kept a solid shape. Fish glue was the easiest of the glues to work with in a mixture with eelgrass although like the homemade casein glue, it foamed upon contact. However, it did not make the eelgrass more brittle while wet. It, like the other animal-based glues, also added a shiny texture to the eelgrass, and after drying, became brittle. Two of the binders, agar-agar and powdered casein glue, clumped so thickly when applied to the eelgrass, that chunks of solid binder added huge amounts of weight to the eelgrass mixture. It was almost impossible to disperse the binder evenly using these binders, and they were not ideal for the method of thatching used because the clumps got in the way of thatching and weaving. After several months of being indoors, the agar-agar began to mold the eelgrass on the sketch models. This means that if agar-agar was to be used as a binder, it would need a preservative to prevent the growth of mold. The concentrations and weights of all the sketch models were recorded, and can be seen in Figure 1 in the appendix.
5.3 Building the Larger Panels Based off these smaller sketch model experiments, it was decided that the best mixture to go with would just be eelgrass and water. As soon as the eelgrass was rehydrated it was useable. Four medium sized panels were made, roughly 50 cm by 24 cm, as well as two larger panels that were 88 cm by 45 cm. The underlying structure was wood, which was notched and glued using wood glue. The spacing and gridding for each structure was different. This was to explore different tectonic varieties. One large panel and one medium-sized panel were based on “loose” thatching, where small-scale vasks were wound around the structure. The other panels relied more on the eelgrass being woven and tucked into the structure, inspired by the Studio Seagrass Væve installation. The panels were so big that it was not possible to weigh them at the school, as there was only a food scale as a resource. However, a mistake in communication meant that a water-based Danish indoor wood glue was used, instead of one more suitable for outdoor use. This would later cause some issues, as the panels were exposed to rain.
5.4 Installing Outside The finishing of the large panels coincided with Danish summer vacation, so it was not possible to complete the installation structure before September. To expose the panels to as much of the weather as possible, the large panels were placed outside on July 27, 2018, on the terrace of Håndværkergården at Copenhagen School of Design and Technology. July was an extremely dry month in Denmark, with fire warnings, and it was not until August that rain began falling regularly again. After about a month, the school reopened for Autumn semester, and the panels were moved to the roof terrace of Guldbergsgade 29N. The exposure to rain dissolved a lot of the water-based glue holding the wooden structure together. In the move, the two large panels that were “loosely” thatched both broke at the top of the structure, removing the top layer of eelgrass. It had rained all day, but where the top layer of thatch met the next layer, it was completely dry, showing that the construction was thick enough that rain could not penetrate the eelgrass entirely. However, using a damp proof membrane in a construction would still be necessary, as the eelgrass on the backs of the panels were wet from the absorption of rainwater. 43
The broken panels were repaired on September 3, 2018, September 7, 2018 and September 14, 2018. A non-water based contact cement was used to fix the top part of the structure, and the notched parts were reinforced with nails. The top layers of both broken panels were then re-thatched. At this point, the newer thatch was different in color than the two month-old thatches, which had begun to turn silver.
The contrast between the sketch models, and the outdoor panels was very visible. The sketch models, which had been inside the whole period, were green and dark brown. The color change appears to happen quickly if the weather is rainy enough. In week forty, the structure for the installation was finally moved to the roof of Guldbergsgade. The panels were installed on boards to be fastened to the installation. The largest panel was screwed into the board, and the structure gave appropriate spacing for the eelgrass to have ventilation and drainage. The other panels and sketch models were fastened to the board by zip ties, again, in order to aid in ventilation and drainage. Once arranged, the installation boards were kept inside until the installation in October. INSTALLATION 3D PLAN by Anke Pasold
5.5 Conclusion Based on Present Data After two months, the eelgrass began to turn silver and solidify. The biggest issues with the thatch panels was poor craftsmanship of the underlying structure, which failed and had to be reinforced, not the eelgrass thatching itself, which remained firmly attatched to the parts of the structure that broke. The eelgrass shed in little pieces off the panels, however, overall, the thatch was well attatched to the structure, and could withstand movement very easily. If the panel structures were better crafted, there would likely be no issues with making large-scale productions of the panels, transporting and moving them around site. Kirstin Lynge, a seaweed thatcher for eight years, visited the panels on September 10, 2018. She noted that if the eelgrass used on the panel was thick enough, it could be factored into the u-value calculation of a wall or roof construction. It would also require the panels to be tightly thatched enough, to prevent cold bridges. This means that if they were properly constructed, the panels could function as supplementary insulation on a building. 45
The next steps in the exploration process are to determine how the seaweed handles the weather in Denmark, especially the different binders with seaweed over time. The strength of the thatching when exposed to the wind is also something that needs to be explored, as well as determining when, if at all, the panels become watertight. Maintainence for the panels also needs to be determined, as well as how long it takes for plants to begin to grow on them. For a traditional seaweed roof, the first maintenance check is after six months, and it will be interesting to see if it is similar for the panels. On the basis of the results so far, with refinement, this method of using prefabricated seaweed thatch could be replicated on a larger-scale on buildings, with different substructures, thicknesses of eelgrass and spacing. A small building mock-up could eventually be built, testing the feasibility of the material in a construction, and the possible affects on indoor climate.
Photograph by KEA Communications
Architecture is often precedent based. Architects often turn to the past, to justify their design and concepts. This creates a circular economy of ideas, as feasible concepts are recycled and refined over time, much like how using eelgrass instead of letting it be waste on the shores creates a circular economy, and supports the material’s own growing environment. The seaweed houses on Læsø are a very strong precedent for eelgrass architecture. They show the feasibility of seaweed as a material, standing for hundreds of years. Vernacular architecture often solved issues related to the local climate, in a low-tech way, with local building materials and techniques. In the case of the seaweed homes, they were able to replace straw and timber that did not grow on the island. Modern construction has distanced itself from this, with the rise of globalization and industrialization. However, as more and more environmental issues arise from our consumption of materials and energy, the industry should once again revisit these old techniques with a new lens. Choosing eelgrass as a material means choosing sustainability. When locally harvested and used, it can create carbon neutral or carbon negative buildings.
Harvesting it can also help reduce nutrient loading in the seas, and contribute to better water quality. It can also help provide extra revenue, if it is seen as a potential material instead of waste. The salt content of the eelgrass means that it does not rot, and that it can act as a fire retardant. History shows, as well, that it performs well as an insulator, and can compete with modern rockwool. Zostera’s insulation product, although more expensive than rockwool, is also a sustainable investment. It is non-itch, as well as non-toxic; this makes it easier to handle than more modern insulation materials. In an era where demonstrably harmful materials like asbestos are being allowed back into building materials in the US, alternative-building materials like eelgrass should be seriously considered as a better alternative (Franklin, 2018).The largest challenge to face eelgrass as a building material will be to convince professionals worldwide to consider investing in it. There is enough to supply the market, but there is little demand at the present. Aesthetically and construction-wise, eelgrass has many possibilities beyond insulation. The traditional method of thatching creates a large, volcanic shaped form of loose, organic eelgrass, which supports many different species of plant life.
Vandkunsten decided to add a degree of order, by netting eelgrass in soft nets, which were then applied to the façade and roof of their Modern Seaweed House. They also used the eelgrass as padding in the inside of their homes, and as insulation in the timber-constructed wall, roof, and floor elements. Ultimately, their construction solution failed, however it successfully influenced other architects to work with the eelgrass and put the Læsø houses in an international spotlight. Studio Seagrass has shown that eelgrass can be weaved neatly into a gridded structure to create playful shapes, and defy gravity. They have also shown that it can be firmly compressed into plates, or pressed into soft, flexible shapes. The prefabrication of Vandkunsten and the experimentation of Studio Seagrass inspired the prefabricated eelgrass thatch panels. The refined technique shows that it is possible to create a product inspired by the original seaweed thatch, but without requiring as much labor or time used. It can be customized with binders, if needed, or without. It can use a variety of substructures to achieve different aesthetics: ordered, or loose like the original houses. Overall, it is a practical solution for modern-day construction. These different uses and applications demonstrate the flexibility of eelgrass in architecture, and hopefully can inspire a new era of experimentation. 49
7.1 Interview with Søren Nielsen, Vandkunsten March 20, 2018 1. Do you think that eelgrass could be used as insulation in different types of buildings- for example, masonry construction? Possibly but measures should be taken to ensure ventilation behind the masonry as masonry is not watertight. 2. Does it have any odor in construction? Not if treated correctly, ie washing off micro algae and properly drying afterwards. Eelgrass cannot rot itself. 3. What are the benefits, in your opinion, of using eelgrass over other insulation methods, like fiberglass or mineral wool? The extremely low environmental impact and the better indoor climate due to its moisture regulating capacity. Constructions without vapour barrier are enabled. 4. Were their any construction alternatives or ideas other than the wool pillows tested for Det Moderne Tanghus? If so, what were they and what were the results? Numerous including braiding and twirling, but we chose the pillows as a way to balance the unruly material with a ‘form-binder’ - the wool-rouse. Attempts to compress the material into straight geometric shapes was not tried as it was against our ideas of designing in respect for the nature of the material. 5. Do you think it is possible to use as a facade/roofing material in buildings throughout Denmark? If so, please explain why. No, 1. there is too little of it, 2. It is somewhat expensive, 3. More experience should is needed before upscaling, 4. Possibly to much maintenance. 6. Are there any challenges that come with using eelgrass, either as a cladding or insulation material? See above! Thank you so much for your help. I will try to take a trip to Læsø at some point and see the house in real life, as well as the viking houses. You should do it for the traditional houses. The modern Seaweed had recently the roof replaced with a wooden roof due to a construction damage; there is no more seaweed on the roof. Perhaps you just need to go to the Open Air Museum in Sorgenfri 10 km north to Cph. where there is a perfect Læsø farmhouse.
7.2 Interview with Tobias Øhrstrøm, Studio Seagrass September 7, 2018 1. What made you interested in eelgrass? The ecological angle, not from an architectural perspective actually. Eelgrass is a fertilizer and can grow plants. 2. What sort of projects has Studio Seagrass been involved in? Installations, like Væve, and products like the eelgrass plates and “pillows”. 3. Regarding the Væve project, what was the substructure? They were individual steel substructures, with the eelgrass woven in. They were separately attatched to the main wooden structure. 4. Was any binder used in the Væve project? No, just dry eelgrass like on Læsø, woven into the steel structure 5. Are you creating any products for the market? Yes, we are looking into having the “pillow” panels manufactured in Jutland We are working with Zostera to create a façade type system with their eelgrass insulation with Convert Factory. 6. That’s the insulation that was made with Advance Nonwoven, right? Yes, it is cradle-to-cradle certified. But it is only fire rated E, which is the second-to-worst fire rating. Our panel is fire rated B. It depends on what binders you use. 7. What binder did they use? They used a plastic-based binder, which isn’t the best. 8. But you use only natural binders? I saw that in your Masters Thesis you had experimented with it. Yes, but only a little bit then, and to see if it could make it a structure. For the last 2.5 years we have experimented with 20-25 different binders, for example, starch, and soy binders. 9. How much eelgrass goes into one of these plates (roughly 20x20cm in size)? Are there any issues that come up with the plates? And how much binder-per-plate is there? Eelgrass is very moisture absorbent, so the binders have to be strong. I think it can absorb up to ten times its weight in water. We use about five to tenpercent binder. There is 1 kg of eelgrass in a plate.
7.2 Interview with Tobias Øhrstrøm - Cont. 10. What are the downsides and benefits of using eelgrass as insulation (Zostera)? It is roughly seven times more expensive than rockwool. But you can handle it without gloves and manually cut it to the right size, because it is non-itch. And it can absorb and release water. 11. Are there issues with getting a supply of eelgrass in Denmark, because it is endangered? Is the dry eelgrass protected? There aren’t really any issues with the supply. There are three farmers that sell it in Denmark, from Møn and Bogø. They are mostly selling it to Germany where it is used in insulation. It is not protected here; you can pick it up on the shore. But it is in other places like in Barcelona. You cannot pick it up from the beach; it’s illegal. Novagrass has also developed a way to farm eelgrass. You can harvest from the plant once a month, without harming it. 12. Are there any other architects at the moment, experimenting with eelgrass? No, to my knowledge we are the only ones.
7.3 Interview with Kirstin Lynge, Zostera September 10, 2018 1. How did your father, Henning Johansen, learn to seaweed thatch? He was a regular thatcher, and often was removing the older seaweed roofs on Læsø to repair them with regular straw thatch. From removing them, he learned how they were constructed, and ten years ago decided to repair one. He had an issue getting eelgrass since there is no more on Læsø, and since no one was collecting it off the beaches at the time or farming it. He found out that it used to be farmed at Møn and Bogø. He ended up contacting the children of the original seaweed farmers, who remembered picking up the seaweed when they were young, and restarting the process of farming seaweed. 2. How long have you been seaweed thatching? For seven or eight years. When I go home on holiday, I help thatch some of the roofs. 3. What is the process of thatching a traditional seaweed house? Two women would twist the seaweed so that one end is thin, and the other thick. Then they are attatched to the house’s roof rafters, up to the third rafter. Pine branches are laid down, and then the rest of the seaweed is piled on top. 4. How did this technique for twisting the seaweed come about? It is very similar to spinning wool, and two women did it by hand. The men were sailors at sea, and the women were left at home on the farms, so it is likely the women came up with the technique. There was no straw because it was all used for animal feed, so they used the seaweed that washed up on the shore. 5. How much seaweed is roughly used in a roof? It is about 80 tons. 6. What is different about the thatching process today? Today we use a machine, which consists of a large spindle connected to a motor on one end, and a drill on the other. One man works the spindle end to spin the large “gumlinger” side, and another on the drill to twist the thinner vask end. After the vasker are attatched to the rafters, a crane drops more bundles on the top of the roof, where people help spread it out and stomp it down. We cut out the doors and windows soon after we make the roof using a chainsaw, and after 6 months, recut as needed. We use about 4 to 7 people to make the roof. 7. Do you think that there is enough eelgrass to supply the industry? Yes. The three farmers from Møn and Bogø alone harvest 400 tons from 2km of coastline. And in the south of Denmark in kommunes like Solerød where they are regularly cleaning the beaches for tourists, the eelgrass is just thrown onto a field and not harvested for use. So there is a huge potential for supplying the industry, if we can convince them to slightly change how they clean the beach. 54
7.3 Interview with Kirstin Lynge - Cont. 8. What are the challenges of using eelgrass in your insulation? It is expensive. It is close to 150DKK per square meter for 100 mm insulation batts 9. What are the benefits of your insulation? It is the only insulation product that is classified as gold with Cradle to Cradle. It is sustainable, because eelgrass helps absorb CO2 and we only heat it to 130 degrees, without using any water in the process. It is a natural fire retardant- we do not need to add any chemicals to make it fire resistant. It is also 100% reusable, we can take the old insulation back, re-mill it and re-process it into a new insulation batt. 10. How much eelgrass is there in a batt? For ten centimeters of thickness, it is roughly 5kg of eelgrass per square meter.
7.4 Table 1
8. References and Works Cited Advance Nonwoven A/S (2016). Måling af lydabsorption ved vinkelret lydnindfald på to materiale - Frearson, A. (2013). The Modern Seaweed House by Vandkunsten and Realdania. [on varianter af hampeplader og en tangmåtte. Hørsholm: DELTA. line] Dezeen. Available at: https://www.dezeen.com/2013/07/10/the-modern-sea weed-house-by-vandkunsten-and-realdania/ [Accessed 14 Sep. 2018] Advance Nonwoven A/S (2017). Test Report. Taastrup: Det Teknologisk Institute, pp.1-4. Initiafy. (2018). How Does Construction Impact the Environment? | Initiafy. [online] Archello. (2018). Modern Seaweed House | Vandkunsten | Archello. [online] Available at: https:// Available at: https://www.initiafy.com/blog/how-does-construction-impact-the-environ archello.com/project/modern-seaweed-house [Accessed 14 Sep. 2018]. ment/ [Accessed 2 Sep. 2018]. Bedre varmeisolering er billigere. (1950). København: Teknisk Forlag, pp.8, 9. Cabot, S. (1923). Heat insulation. Boston, Mass.: Samuel Cabot Inc., pp.1-9.
Iucnredlist.org. (2018). Zostera marina (Eelgrass). [online] Available at: http://www.iucnredlist. org/details/153538/0 [Accessed 2 Sep. 2018]. Jensen, J. Kaarup (2012). Tængemænd og vaskerpiger. [Randers]: Projektmageriet.
Cradle to Cradle. (2018). Seaweed Insulation | C2C-Centre. [online] Available at: http://www.c2c-cen tre.com/product/building-supply-materials/seaweed-insulation [Accessed 14 Sep. 2018]. Jensen, J. Kaarup (2014). Naturens eget tag. Dennis, F. (2018). FireWise Plant Materials. [online] Static.colostate.edu. Available at: https://static. colostate.edu/client-files/csfs/pdfs/06305.pdf [Accessed 14 Sep. 2018].
Kaushik. (2018). The Seaweed Houses of Læsø Island. [online] Available at: https://www.amus ingplanet.com/2018/02/the-seaweed-houses-of-ls-island.html [Accessed 14 Sep. 2018].
Dollerup, H. and Skov, C. (2004). Forsøgsplatform og imprægnering & Lane, T. (2010). Embodied energy: The next big carbon challenge. [online] Building. Substitution af Bor- afprøvninger. [online] Skanderborg: Energistyrelsen, pp.19, 20. Available Available at: https://www.building.co.uk/technical/embodied-energy-the-next-big-car at: http://www.alternativisolering.dk/download/Substitution%20af%20bor%20-%20af bon-challenge/5000487.article [Accessed 14 Sep. 2018]. pr%C3%B8vninger/rapport200575664000064.pdf [Accessed 14 Sep. 2018]. Lynge, K. (2018). The Historical Thatching Method on Læsø and Zostera Insulation. Ecochunk.com. (2018). ‘Neptune Balls’ finally find some use as environmentally friendly insu lation. [online] Available at: http://www.ecochunk.com/6777/2013/03/09/neptune-balls-final Miles, P. (2008). The Danish revival of seaweed thatching | Financial Times. [online] ly-find-some-use-as-environmentally-friendly-insulation/ [Accessed 2 Sep. 2018]. Ft.com. Available at: https://www.ft.com/content/88e55922-749f-11dd-bc91- 0000779fd18c [Accessed 14 Sep. 2018]. EPA. (2018). The Sources and Solutions: Agriculture | US EPA. [online] Available at: https://www.epa. gov/nutrientpollution/sources-and-solutions-agriculture [Accessed 14 Sep. 2018]. Naturalhomes.org. (2018). Seaweed Thatch. [online] Available at: http://naturalhomes.org/seaweed-house.htm [Accessed 14 Sep. 2018]. Fabrin, P and Øhrstrøm, T. (2018). studio seagrass. [online] Available at: https://studioseagrass.cargo collective.com/ [Accessed 2 Sep. 2018]. Nielsen, S. (2018). The Modern Seaweed House. Fluencecorp. (2018). Denmark Policies Balance Water Quality, Food Demand | Fluence. [online] Available at: https://www.fluencecorp.com/denmark-policies-balance-water-quality-food-de mand/ [Accessed 14 Sep. 2018].
Nielsen, S., Klebak, A. and Søndermark, J. (2013). Det moderne tanghus på Læsø. [Odense]: Realdania Byg.
Novagrass.dk. (2013). Novagrass | Ålegræs | Eelgrass. [online] Available at: https://www.nova Franklin, S. (2018). EPA is now allowing asbestos back into manufacturing. [online] Archpaper.com. grass.dk/en/ [Accessed 2 Sep. 2018]. Available at: https://archpaper.com/2018/08/epa-asbestos-manufacturing/ [Accessed 14 Sep. 2018]. Øhrstrøm, T. (2015). bio-concretion. Masters. Advanced Architecture of Catalonia. Øhrstrøm, T. (2018). Studio Seagrass. 57
8. References and Works Cited - Cont. Plawecka, A. (2015). Seaweed insulation. Undergraduate. VIA University College, Horsens. Realdania Byg (2013). The Modern Seaweed House. [video] Available at: https://www.you tube.com/watch?v=quyrglWd7vw&t=379s [Accessed 14 Sep. 2018]. Schrieber, R. and Gareis, H. (n.d.). Gelatine handbook. Wiley. Tangtag (2018). [online] Available at: http://www.tangtag.dk/glbeskrivelser [Accessed 2 Sep. 2018]. Vejr.tv2.dk. (2018). [online] Available at: http://vejr.tv2.dk/2018-05-30-ekstrem-varme-koeben havn-ramt-af-tidligste-hedeboelge-i-145-aar [Accessed 2 Sep. 2018]. Visitlaesoe. (2018). Seaweed houses on Læsø. [online] Available at: https://www.visitlaesoe.dk/ ln-int/laesoe/museums/seaweed-houses-laeso [Accessed 2 Sep. 2018]. Widera, B. (2014). Possible Application of Seaweed as Building Material in the Modern Sea weed House on Læsø. [online] Wroclaw, Poland: 30th INTERNATIONAL PLEA CONFER ENCE. Available at: http://www.plea2014.in/wp-content/uploads/2014/12/Pa per_8A_2158_PR.pdf [Accessed 14 Sep. 2018]. Wittchen, A., Linnet, L., Devantier, A., Knudsen, L. and Zibrandtsen, A. (2018). Eelgrass - a socio-technical material study. Masters. AAU-CPH.
7th Semester Dissertation on seaweed as a building material in Denmark: the history, benefits, past and possible future applications.
Published on Oct 7, 2018
7th Semester Dissertation on seaweed as a building material in Denmark: the history, benefits, past and possible future applications.