Seaweed as Building Material

Seaweeds are marine resources of non-flowering plants. It grows submerged in intertidal, shallow and subsurface water up to 100 m depth in the sea, brackish water estuaries. Most seaweed belongs to one of three divisions – the Chlorophyta (green algae), the Phaeophyta (brown algae) and the Rhodophyta (red algae). There are about 900 species of green seaweed, 4000 red species and 1500 brown species found in nature. Researchers at Fraunhofer Institute for Building Physics (IBP) found a way to utilize species of seaweed by using it as insulation material or as cladding in construction field. It has been reported that addition of sea weed can hold 20 percent more energy than wood or wood products. Some non-edible seaweed has gelling, thickening properties, binding capacity, and corrosion resistance properties. Many types of seaweeds have many uses, from direct use in dishes or as food supplements, pharmaceutical, fertilizer or biodiesel resource.

In Germany (Tunisia and Albania sea), the seaweed leaves from the Posidonia oceanica plant, more commonly known as Neptune grass seaweed, is virtually nonflammable, resistant to mold, and can be used as insulating material without the need for chemical additives. It can be used as insulation between the rafters of pitched roof, to insulate interior walls, or to reduce the amount of heat lost through building envelopes. Fibers act as a buffer, absorbing water vapor and releasing it again without impairing its own ability to keep the building insulated.

In United Kingdom, seaweed was used as a polymer in natural clay bricks. Bricks are made by the usual method, burning of bricks is not required due to the utilization of seaweeds. The un-burnt bricks made of seaweed resulted in compressive strength two times higher as that of ordinary clay bricks. Alginate is a natural hydrophilic polymer extracted from seaweed. Seaweed extract also used as a water repellent layer over the bridges.

How is seaweed processed into a building material?

Seaweed fibres act as a buffer, and with a salt content of just 0.5 to 2 percent, Neptune balls / Sea balls can be used to produce insulation material that will not rot away. Processing, Neptune balls into fibres is a difficult task, as it is not easy to remove adherent sand from the Neptune ball. In addition, individual fibres tend to catch easily on anything, including one another, and are quick to form new clumps both during processing and later when being blown into spaces in need of insulation. However, new methods for turning Neptune balls into viable insulating material have been developed by the Fraunhofer Institute for Chemical Technology ICT, in collaboration with other industrial partners. The project partners’ aim was to produce an insulating material capable of being stuffed or blown into the required space without difficulty.

“Shaking the Neptune balls proved the best way of making sure we end up with fibres that are as long as possible and free of sand,” says Dr. Gudrun Gräbe from Fraunhofer ICT. By carefully breaking up the clumps, Gräbe and her team were able to find the best way of acquiring fibres. Once all sand has been removed from the balls, a conveyor belt delivers them to the cutting mills, from where 1.5 to 2 centimetre fibres emerge undamaged and drop into plastic bags.

The Fraunhofer Institute for Building Physics IBP in Holzkirchen found that the loose insulating material produced is capable of holding a considerable amount of energy – 2.502 joules per kilogram kelvin (J/kgK) – which is 20 percent higher than that of wood or wood products. This means that the fibrous material can keep buildings cool in hot weather, and shielding them from the heat during the day. An analysis was done, confirming how well Posidonia fibers insulate heat.

Finally another advantage of Neptune balls is that they are environmentally friendly – the entire manufacturing process requires very little energy.

The Modern Seaweed House by Vandkunsten and Realdania Byg

Seaweed pillows were used as cladding for this holiday house on the Danish island of Læsø by architecture studio Vandkunsten and non-profit organisation Realdania Byg.

The Modern Seaweed House revisits the traditional construction method in Læsø, where for many centuries trees were scarce but seaweed has always been abundant on the beaches. At one stage there were hundreds of seaweed-clad houses on the island but now only around 20 remain, which prompted Realdania Byg to initiate a preservation project.

Insulation like Mineral Wool

Eelgrass insulates and its insulation value is close to comparable to mineral wool. Rather than just piling the seaweed onto the roof, the designers stuffed the material into netted bags and attached it in lengths across the timber-framed walls and roof of the house. More seaweed was enclosed in wooden cases to use as insulation behind the facade and beneath the floors. The eelgrass is also used as facade cladding.

Keeps CO₂

Lifecycle analysis indicates this house is actually ‘carbon-negative’ as the amount of C02 accumulated by the seaweed walls and roof exceeds the C02 emitted during transportation and production of its building materials. 

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.

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 of potential, it has been discovered through practical application that seaweed has 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 numerous qualities provide a wide range of applications in modern, sustainable building.


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