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But how can this new concept be measured? In short, it can be analysed as a measure which will help select them correctly, and it can be studied based on the environmental impact the materials may generate during their life cycle in each of their groups. 

Natural stones

The materials originating from natural stones require high energy consumption in their extraction and transport phases due to their excessive weight, although their great durability works in their favour. In addition to this, metals cause considerable environmental impact in the recovery stage, but are highly recoverable throughout the process (scrap is the treasure of work sites).

Plastics

Plastics demand high energy consumption in the recovery phase, but in compensation they are light, tough and greatly appreciated as insulating materials, which has a positive effect on the energy efficiency of the home. 

Wood

And finally, wood is one of the most sustainable of the conventional materials and is the only one which combines two essential aspects in bioclimatic architecture - it is renewable and recyclable at the same time.

In this way, and by virtue of the different phases of their life cycles, the sustainable construction materials would be those which combine most of the following characteristics: coming from renewable sources, abundant and produced fairly; durability; lightness; recoverable and cheap; and of course, they must consume little energy. 

Regardless of the others, the three final points must be achieved if conventional, local materials are used, a choice which will directly contribute to reducing the environmental impact through the energy saving attributable to transport.  

Building with recycled or "scrap" materials

Among the sustainable construction materials, a separate chapter must be opened for all types of product whose original function was something other than a building medium, but which in the final phase of their life cycles, the waste phase, have been recovered for this purpose. 

This is building with recycled materials, an initiative which stemmed from the inventiveness and imagination of architects and ecologists all over the world, who have taken advantage of the abundance of some specific waste in their environment in order to build "eco-houses" and "eco-environments", by creating structural and decorative elements for them. 

The scrap materials most used for this type of building, which usually combines bioclimatic principles with the use of renewable energies in the projects, include wheel rims and tyres, tins, bottles, wood waste, pallets, containers, train rails, ship rubble and industrial rubbish, to quote some of the best-known ones. 

However there are no limits to building with scrap materials and any new waste is always welcome. In fact, many of these initiatives have the approval of local and regional government due to their contribution to sustainability and the reduction of the environmental impact in their operating areas, and because they provide an unbeatable way of having decent homes for disadvantaged people. 

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