What alternatives to "all concrete" in the Indian Ocean?

Historically, the traditional Creole hut was "geo and biosourced".

In Reunion Island, as in the rest of the Indian Ocean, the building materials used by men have always been historically coming from a close environment: Traveller's tree, Latanier, Vetiver... It is only since the years 1950/60 and the arrival of "all concrete" constructions coming from the post-war reconstruction in Europe that the Indian Ocean territories started to change their construction mode: the traditional Creole wooden hut was slowly lost to be replaced by imported building materials (particleboard, concrete, etc). It is only since the 1950s/60s and the arrival of "all-concrete" constructions from post-war reconstruction in Europe that the Indian Ocean territories have begun to change their construction methods: the traditional wooden Creole hut has been slowly lost and replaced by imported construction materials (cinder block, cement, sheet metal). This radical change in construction methods and principles is mainly due to the strong demographic growth and the need to house the growing population of our territories.

Exemple de case créole en bois

The manufacture of 1m3 of concrete emits more than 270 kgCO2 eq in Réunion*.

In a context of climate change, it is necessary to reduce the carbon impact and the use of resources of our constructions. The building sector (construction and operation) is responsible in France for :

  • 40% of energy consumption
  • 50% of the consumption of natural resources (quarries, wood, water, oil, etc)
  • 40% of CO2 emissions
  • 50% of waste production

In Reunion Island, the construction phase represents up to 30% of the building's CO2 emissions over a 50-year life span. To reduce the environmental impact of the building sector, alternatives to the current construction methods exist, in particular through the integration of bio-sourced materials. The different territories of the Indian Ocean offer a wide range of alternative construction solutions.  

School Rue Pothier in Saint-Paul, Photograph : Frédéric Lancelot

Wood, a carbon sink

In Reunion Island, wood is used for solar protection, for the framework, and more and more in the envelope as a load-bearing element (wood-frame wall, wood floor, etc.). Wood contains carbon that has been removed from the atmosphere during the growth of the tree, thus creating "carbon sinks". The use of a wood floor (CLT) compared to a concrete floor allows, for example, to reduce the carbon emissions of the project by 170kgCO2 eq/m² SU according to the TEC-TEC tool. In addition to the carbon aspect, wood has many advantages. On the thermal level, wood is an effusive material that stores little heat. Concerning the building site, prefabricated wood elements are faster and cleaner to implement.  

Subject to respecting the good practices on the choice of the essence, of protection against moisture or the attacks of insects, the use of wood is perennial in Reunion.

The expansion of BTC in Mayotte

The BTC (Compressed Earth Brick) is mainly used in traditional constructions in Mayotte. The compressed earth brick is a derivative of adobe, one of the first building materials used by man. It is made from sifted clay, moistened and then compressed in molds by a mechanical press. It is used in the shell (base), as a filling wall (wood frame for example) or as a partition.

BTC is a circular material that can be recycled without much energy input. The earth resource is abundant and can be used directly on the construction site while avoiding the depletion of quarries. The overall carbon footprint of the BTC is low: less than 20kgCO2/m² of façade. Indeed, the BTC requires little transformation and very little transport compared to other materials coming from a more carbonated sector such as cemented / tarred products.

The BTC sector and the technical rules are being structured in Mayotte. Many ambitious projects use this material.

Example of a project in Mayotte using BTC, LYCÉE DES MÉTIERS DE LONGONI, Vice rectorat de Mayotte

Encore Heureux associated with Co-Architectes

Towards biosourced and geosourced insulation?

There are a number of biobased insulating materials available, including straw, cellulose wadding, wood fibers and hemp wool. On Reunion Island, bagasse, guava, cryptomeria and vetiveria have been identified as potential sources of insulation. However, it remains to be seen how to develop and structure these products.

In order to be deployed effectively, plant fiber-based insulation products, like traditional products, must meet a certain number of conditions for use: suitability for use, resistance to fire, humidity, insect and mold attack, etc. The incorporation of antifungal substances, insecticides or other biocides may be necessary to ensure the long-term performance and durability of such insulation products.

Numerous other local initiatives exist to reduce the environmental impact of construction in the Indian Ocean: development of the bamboo sector, plant-based concretes, recourse to reuse, etc. Since 2004, INTEGRALE Ingénierie has been helping owners and contractors in the Indian Ocean to reduce the environmental impact of their buildings.

*equivalent to 1.5 flights Réunion / Mayotte.
  • BioRev'Tropics - The use of local materials by construction in the tropics, 2018, Nomadéis, BioBuild Concept, LEU,
  • ISOBIODOM - Biosourced insulation in overseas departments, CIRBAT, FCBA, CSTB
  • Professional rules for compressed earth blocks Mayotte, 2022, A.MISSE, CRATERRE, ART.TERRE, DEAL MAYOTTE
  • TEC-Tec and MAY-Tec tools
  • TROPIKACV, University of Reunion, LAB PIMENT, Integrale Engineering, CSTB

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