The idea was conceived in foundation Readania Byg who is the client. They had previously completed a project for conservation of the remarkable traditional seaweed-thatched houses on the island of Laesoe. This project is located on a site next to the modern seaweed-house. The idea is to re-introduce overlooked or disregarded organic materials to a modern industrialized technology at a time where low-carbon solutions are much called for. The objective is to demonstrate how a natural resource like seaweed can be integrated in a contemporary construction practice and an ordinary use. Also, the project is meant to inspire and encourage to further exploration into alternative materials by showcasing how architectural identity can be generated from these.
The focus is on the use of the seaweed material and how this, together with the wooden construction, can bring the carbon-footprint down to a very low level. In this, the strategy differs from low-energy concepts aiming entirely at minimizing energy use for operation. However, the energy used for operation is very low in the seaweed house due to passive measures such as high insulation thickness, airtight assembly, heat recovering system, heat-pump, and low-energy windows. The house lives up to the strictest standards for low-energy buildings in Denmark with an expected consumption of 20 kWh/year/m2.
Very much energy is saved by using seaweed and wood instead of materials like concrete, steel, aluminum, bricks and mineral wool. This was found in the lifecycle assessment provided by an external consultant, stating that there is a negative carbon-footprint of 8.500 kg CO2 in the building. This means that the building through its materials is 'ahead' of energy consumption for operation. How long it can be operated before the carbon-footprint obtains positive values depends on the kind of energy provided - in Denmark, at the present it is a mix of waste combustion, natural gas and wind power. There are three kinds of use of the seaweed: 1. For insulation (not visible): The house is constructed with timber-frame panels stuffed with seaweed as an alternative to mineral wool. 2. Exterior cladding: The roofs and facades are clad with pillows (firm cylindric cushions) of seaweed made as knitted hoses of wool, stuffed with seaweed. On the roof the pillows are thick and soft, on facades they are small and hard and arranged as 'battery packs' in prefab panels. It is important to remark that although the seaweed elements has been produced as a work of craftsmanship all processes can be performed as industrial production if the volume is sufficiently large. 3. Interior cladding: The picked ceiling is covered with panels stuffed with seaweed and upholstered with linnet fabric.
The house is supposed, and expected, to have the same lifetime as any other building. Having said that, the construction technique for the exterior cladding is unprecedented and hence its exact lifetime is not known so far. The seaweed material is however extremely robust as it does not rot, mold or attract pests. However, over time we expect plants and birds to inhabit the roof as part of its weathering. Like wood seaweed turn silver grey within a year's time. To ensure the technical quality of the roof there is a dens layer of roofing felt below the seaweed thatching. The house will be used as a holiday residence with a bed capacity for 8 persons. The building is used as an ordinary holiday residence or it might be used as a whole year residence due to the ambitious low-energy performance. There is no specific maintenance required as a consequence of the seaweed components.
The cultural heritage of Læsø: A resource in sustainable building
On the small island ofLæsø in Denmark, aseveral hundred-year-old building style has formed the basis on which a new holiday house has been built – the Modern Seaweed House. The house is designed by Vandkunsten firm of architects and developed by Realdania Byg as a holiday house built in wood, covered and insulated with seaweed. The Modern Seaweed House is carefully adapted into the landscape and has a wonderful interaction with nature, the historic buildings and Læsø's unique cultural history. The Modern Seaweed House is now to be sold – but the ideas live on.
The Modern Seaweed House is part of the Realdania Byg project 'Seaweed Houses on Læsø' that also includes 'Kaline's House' – a listedseaweed house from 1865, purchased and carefully restored by Realdania Byg in 2012. The seaweed houses on Læsø are an exceptional part of the cultural heritage of Denmark – and the world.Originally, several hundred of these seaweed houseswere found all over Læsø while only approximately twenty remain today. The traditional seaweed houses were built using a timber frame construction with robust seaweed roofing – an abundant resource in the small and modest fishing community. 'Kaline's House' is one of these houses.
'The seaweed houses on Læsø are physical testimony to the culture and the life that have characterised the building tradition on the island for centuries. The starting point of the Modern Seaweed House has been to explore this unique archive of cultural and architectural history and employ the past as source for contemporary architecture. It is our hope that others will embrace the experiences from this project and develop the ideas even further,' says Peter Cederfeld, managing director of Realdania Byg.
The Modern Seaweed House is not a replica of the building style of the past but a development inspired by the architectural history of Læsø. In contrast to the historic houses, on which the seaweed is stacked high on the roof, the Modern Seaweed House is more contemporary and tight in its expression. The visible seaweed has been stuffed into bolsters made of knitted nets attached to the façade in lengths. At the same time, seaweed is used invisibly for insulating floors, walls and ceilings enclosed in wooden cassettes.These prefabricated building modules comprise the framework of the house.
A sustainable resource When seaweed was used in the past as a building material it was due to the fact that seaweed was found just outside the door, it was free, had a long-term durability, was very effective as insulation, naturally protected against vermin and putrefaction, and,finally, there was lots of it. These very preconditions make seaweed of current interest as a building material, especially in the light of the present attention to the topic of sustainability. The Modern Seaweed House fulfils expected 2020 demands, and, thereby, will have extremely low energy consumption.
At the same time, LCA (life cycle analysis) calculations have shown that the house actually has a negative carbon footprint. The almost exclusive use of organic materials, including seaweed used as both insulation and roofing material,causes the amount of CO2 accumulated within the house to exceed that which has been emitted during the production and transportation of the building materials.
'By using seaweed in the construction, we not only secure the continued supply of seaweed for use on the historic houses, we also reintroduce a material to the modern building industry which is CO2-reducing, environmentally friendly and sustainable in a broader sense,' says architect and project manager in Realdania Byg, Jørgen Søndermark.
In a broader view With the'Seaweed Houses on Læsø' project,Realdania Byg wishes to focus on the unique tradition of Læsø using seaweed as a building material – both the immediate need to ensure the architecture of the past and the at least equally relevant need to develop the architecture in a sustainable approach.This way, seaweed is also ensured for restoring the historic houses.
Realdania Byg's project to develop and preserve seaweed houses on Læsø is one among a variety of existing projects that aim to secure the survival of the distinctive seaweed roofs on Læsø. The initiative is carried out in unison with enthusiastic inhabitants of Læsø, other foundations as well as the Danish Agency for Culture who are all involved in the effort to save this rather exceptional part of the cultural heritage of Denmark – and the world.
The Modern Seaweed House has shown that eelgrass has a lot of qualities. Besides its excellent insulating property and long-term durability, which in itself offer a lot ofpotential, it has been discovered through practical application that seaweedhas exceptional acoustic properties. This creates surprisingly comfortable rooms while the ability to absorb and give off moisture contributes to regulate a good indoor climate. The numerousqualities provide a wide rangeof applications in modern, sustainable building.
For additional information, please contact: Managing director, Peter Cederfeld, Realdania Byg, Phone: +45 70 11 06 06 / [email protected] Architect and project manager, Jørgen Søndermark, Realdania Byg, Phone: +45 32 88 52 65 / [email protected]
Facts
The Modern Seaweed House The Modern Seaweed House is built from prefabricated wooden cassettes that comprise the floor, façades and roof. Seaweed is featured as insulation within the cassettes themselves, as padding inside the acoustic ceiling draped in flax as well as for cladding both the façade and the roof. In contrast to the historic houses, on which the seaweed is stacked high on the roof in a tall, swelling, mushroom-like fashion, the Modern Seaweed House is more contemporary and tight in its expression. The visible seaweed has been stuffed into bolsters made of net knitted in strong wool. The bolsters are attached to the roof in overlapping runs and, in smaller scale, mounted on the façades using the same method.
The house is designed by Vandkunsten firm of architects and erected 2012-2013. The prefabricated elements have been made at Green House in Kongerslev who have also been lead contractor on the construction and assembly of the house on Læsø. The padded ceiling elements have been made at Brian Liebeck in Frederiksberg on frames by Fab Lab in Næstved, while Praktisk Service in Stege along with trained thatcher Helle Raknes have been in charge of the production of the seaweed cladding. The seaweed comes from the two manufacturers on Bogø and Møn, respectively, who can provide the crucial seaweed of a decent quality after the seaweed plague destroyed most of the larger natural occurrences, including those south of Læsø, back in the 30s.
The house is 100 square metres and is built for two families: Centrally located is a large family room with a kitchen, which is bounded to each side by a core containing technical installations as well as bathroom and toilet. Behind these cores, in each end of the house, there is a very large roomthat can be divided into two reasonable rooms – and above this, a bed loft is located allowing for more sleeping places. The house is heated via a high-efficiency heat pump placed in an adjacent shed that can also be used for storing the families' bikes, summer gear as well as a washing machine and a tumble dryer. The house is tight and effectively insulated and fitted with an efficient ventilation system with heat recovery. The effective insulation makes it possible in effect to live in the house year-round, or for instance maintain a constant temperature of minimum 10 degrees throughout the winter, making the house frost-free.
The Modern Seaweed House is situated on the northern part of Læsø at 6 Tangborgvej next to two other significant houses: Realdania Byg's listed seaweed house, 'Kaline's House', which was restored and refurbished prior to its inauguration in 2012, and today rented as a summer house, and Hanne Kjærholm's summer house for the Rude family erected 1985-1987.
The house is now to be sold at market price.
Seaweed houses on Læsø The seaweed houses on Læsø are an exceptional part of the cultural heritage, domestically and globally. Only very few seaweed houses still exist: approximately twenty in total, out of which eleven are listed. One of these houses is 'Kaline's House', which Realdania Byg purchased and restored in 2012. At the time of acquisition, the house still had its original seaweed roof. The house was built more than 150 years ago and has 80 square metres of floor space. Kaline is a contraction of Karoline, which was the name of aprevious inhabitant of the house. The house has now been carefully restored for posterityand remains as one of the few physical testimonies to the culture and the life, which have characterised the development on this beautiful island in northern Kattegat since the 1200s. 'Kaline's House' was the first leg of the Realdania Byg project 'Seaweed Houses on Læsø', while The Modern Seaweed House makes up the second.
Since the first registration in the 70s, inhabitants of Læsø and friends of Læsø's unique building style have fought to save the last remaining seaweed houses.With support from the Danish Nature Agency, a pilot project in the middle of the 90s revived the old techniques at an old seaweed farm, but it suffered from a lack of proper local seaweed.Within the past years, however, good and healthy eelgrass has surfaced in the Baltic Sea. This has coincided with people of Læsø resuming the struggle to attract outside attention to the cause, and, in 2008, support from several foundations has ensured that two local farmers on the coasts of Møn and Bogø have been able to take up the trade of their ancestors with systematic collection and drying of eelgrass. Previously, eelgrass from this area was – among other usages – used in mattresses, in Denmark branded as Getama – an acronym for Gedsted Tang Madrasser(Gedsted Seaweed Mattresses).
At the same time, support was given to another pilot project, this time with good seaweed laid on an entire roof of a smaller building. Thus, the work to retrieve skills and methods took a step further. As the first half of the third pilot project, the Danish Culture Agency has bought and restored one of the listed seaweed houses, 'Andrine's House' on 1 Alleen. The second half of pilot project number three is Realdania Byg's old seaweed house, 'Kaline's House', which was completed in the summer of 2012 following the full restoration and refurbishment. The Modern Seaweed House constitutes the fourth leg of the course.
