The many different materials used in the construction of a building are not all equal in terms of environmental impact.

• At the start, these construction materials are made from raw materials such as ores, oil, wood, or plant origin.
• Then, these materials require energy consumption, first to transform and process them, then to transport and use them.
• And, in the choice of materials, you have to also look at the impact from dismantling them and their end-of-life impact (recycling, destruction).

As the environment takes on increasing importance and demands our attention, GSE has prepared an analysis of this impact, on a material-by-material basis… and the results can be surprising.

		The different raw materials
		The mineral products which are at the source of building materials are generally abundant in nature. The resources themselves – iron, aluminium, silica, limestone, clay… - generally do not cause environmental problems. However, we particularly need to focus our attention on their management, as processing these materials requires a great deal of energy.     Oil is a raw material, the main component in many insulation materials, plastics, road toppings and other. Production of these and other materials uses a non-renewable natural resource – oil – and, the energy required to make these materials is fairly low, and this is a worthwhile use of oil resource – much more so than simply burning oil to produce energy.   Some materials – in particular PVC – create problems when they are being dismantled, and must be studied on a case-by-case basis. Polyurethane foam insulation used a CFC gas as an expansion agent for several years. When constructions built with these materials were dismantled, CFC gases were released and had impact on the ozone layer. Today, the expansion agents used in foam insulation are CFC-free gases.   Materials of plant origin, in particular wood, have a positive impact on the environment and on CO2 emissions. Everyone knows that plants absorb and sequester the CO2 in the atmosphere for their growth and for photosynthesis. Growing trees are the greatest absorbers of CO2, whereas adult trees considerably reduce their intake of CO2. Good forest management entails logging adult trees and replanting new trees to regenerate the forest. In essence, this creates a large-scale CO2 absorbing and sequestering machine.     In nature, nothing is lost, nothing is created, everything is transformed… Thus the CO2 absorbed and sequestered in the wood returns to the atmosphere at the end of life, either through burning or through rotting. However, given that a building’s life is approximately 30 years, when the wood is destroyed after the 30-year (or longer) lifetime, we can hope that we will have gone beyond the critical threshold of the C02 impact on the greenhouse effect. For in 30 years, oil and coal should no longer be a major source of energy. Thus, the materials research with respect to their environmental impact undertaken here concentrates on the CO2 impact created by manufacturing, transporting and using these materials. Analysis of this impact, on a materials-by-materials basis, can come as a surprise and diverges from what may be commonly thought.

		Here is a list of CO2 impacts for some of the commonly used building materials
		(values expressed in C02-equivalent kgs) 60 kg : 1 m² of concrete roadway.  22 kg : 1 m² of asphalt topped roadway.      21 kg :   1 m² rock wool thermal insulation (K = 0.40 w/m2/°C).   10 kg :   1 m² polyurethane foam thermal insulation (K = 0.40 w/m2/°C). 8 kg :     1 m² expanded polystyrene thermal insulation (K = 0.40 w/m2/°C). 2.6 kg :  1 m² hemp wool thermal insulation (K = 0.40 w/m2/°C).    85,800 kg :   steel structure for 1,000 m² warehouse. 37,530 kg :   reinforced concrete structure for 1,000 m² warehouse. - 45,825 kg : wood structure for 1,000 m² warehouse.     80 kg :     1 m² of roofing, sheet metal underside, rock wool insulation (K : 0.40),                 asphalt sealing. 32 kg :     1 m² polyurethane foam sandwich panel roofing (K : 0.40). - 136 kg : 1 m² wood supported roofing, hemp wool insulation (K : 0.40),                  PVC sealing.     7,040 kg : 100 m² double glazed windows on aluminium frame. 5,000 kg :  100 m² double glazed windows on steel frame.   40 kg :      100 m² double glazed windows on wood frame.      47 kg : 1 m² double skin cladding, rock wool insulation (K : 0.40).  32 kg : 1 m² sandwich panel cladding.

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		This shows that an asphalt topped roadway is more acceptable than a concrete road. Insulation using oil products such as expanded or extruded polystyrene are, quite surprisingly, more acceptable than rock wool insulation, due to the fact that the manufacturing of rock wool requires a great deal of energy. New plant fibre insulation such as hemp, cork, cellulose, sheep wool and others are all acceptable. Production of such fibres is reaching the industrial scale and prices are becoming competitive. The future will see increased use of such materials. Lastly, aluminium is a material which requires enormous amounts of energy. It appears necessary to reduce the use of aluminium to the greatest extent possible.