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Algae, a new eco-material for construction?

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Crucial elements of biodiversity and source of food, algae suffer from a somewhat negative image, especially during the great green tides which are particularly troublesome in summer. However, their usefulness is declined in multiple fields, and especially that of construction. An excellent natural insulator known for several centuries, seaweed is a first-class “eco-material”, with a negative carbon footprint, which in the current context of sustainable development could finally benefit from renewed attention.

Seaweed, an insulating material and a powerful source of energy

Often regarded with disgust during the great green tides and deemed unnecessary, seaweed nonetheless offers multiple advantages in a large number of fields, and particularly that of construction. Algae are practically non-flammable, and do not rot.

Once cleaned, dried, chopped and compacted, they give the appearance of a kind of vegetable wool whose fibers cling to each other by themselves without any chemical additives, and are an excellent thermal insulator. This insulating performance is even 20% better than that of wood, which is already one of the best thermal insulators, nearly eight times more effective than concrete.

A French star-up, Ennesys, even pushed the ecological potential of algae even further, by developing the concept of buildings with walls of energy-producing algae. Inside these walls are transparent tubes housing very living microalgae, continuously fed by injections of CO2 and wastewater. Organisms both capture CO2 to produce oxygen, but also feed on dirty water. Once the phytoplankton has developed, it is removed from the tubes to in turn serve as gas or vegetable oil.

The walls also benefit from the naturally insulating capacities of algae, which ensures that the entire building produces energy that is much higher (and more important than solar panels) than its own needs. The building is then a Positive Energy Building (BEPOS), which will ultimately be the legislative objective sought by RT2020 for all new buildings. Ennesys technology is already actively tested at La Défense.

Seaweed houses in Denmark

On the Danish island of Læsø in the North Sea, the use of seaweed in construction is the main element of habitat. This is an ancestral technique mastered for several centuries by the inhabitants of the island, based on the abundance of algae present on the beaches, which compensated for the low availability of wood on the island.

These inhabitants, mainly from a fishing community, had already perceived the remarkable insulating power of the algae, while offering the advantage of not rotting. These hundreds of Læsø until the 19th century, these houses while algae saw their numbers drop to only 20 before receive protection mission.

The new houses are now made with contemporary methods, and benefit from a wooden frame, more solid and just as ecological. The seaweed remains nonetheless a major material in construction; collected as originally from the beaches surrounding the island and dried, it is compacted in knitted nets which leave it clearly visible. These nets are then fixed on all the facades of the houses, as well as on the roofs. Seaweed is also used invisibly to reinforce the insulation of wooden walls and ceilings.

In the end, these houses constitute totally ecological habitats, with a negative carbon footprint: the greenhouse gases trapped by algae and wood greatly exceed the total amount of energy required for construction. The thermal and acoustic insulation is exceptional, considerably reducing the energy expenditure of residents. Even in terms of durability, these houses don't have to be ashamed of concrete: according to the builders, the inhabitants and their descendants are at least a century and a half away.

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