Natural building materials. Smaller environmental impact, greater opportunities for sustainable construction.

Natural building materials are somewhat fashionable these days but are often used to veneer otherwise conventional buildings to make them look "greener", or even to compensate the greenhouse gases emissions of high-impact materials thanks to their negative embodied CO₂. Against such shallow and sometimes dishonest behaviours, a much more radical approach needs to be taken.

One first relevant point is that we don’t actually know much about natural building materials as such, that is, in their untransformed state. A die-hard prejudice exists, that postulates that materials need to be transformed or improved (e.g. by engineering them) in order to obtain acceptable performances, for instance in terms of reliability, durability. A better understanding of the natural materials available, and a knowledge of how to maximise the results that can be obtained from their properties, are much needed. Often these materials are not covered by standards, and when they are, their characteristics are underestimated or only partially recognised; they do not function as predictably as industrial materials.

Organically grown, little processed materials of natural origin should attain brilliant assessments in terms of environmental impacts, but again, they are seldom covered by LCA databases, which tend to provide values for conventional manufacturing. Sometimes the values are dazzling: for instance, in ÖkoBauDat (ÖBD) the embodied energy (EE) value for straw is seventy times higher than that found in the Inventory of Carbon and Energy. In ÖBD, the EE value for straw is higher than that of structural steel and more than three times higher than that of fired, solid bricks, whose production must require much more energy.

Materials of natural origin are not dangerous to inhabitants and other living organisms, provided no toxic chemicals are added. Preservatives and other chemicals encourage inhabitants to behave irresponsibly and architects to make bad design choices. The addition of substances such as glues and paints makes plant-based materials special waste, which cannot even be burnt at the end of their use life. In contrast, careful selection and processing of raw materials, competent design and maintenance, and frequent replacement of parts can produce very durable buildings. Food labels must state the ingredients, but it is not compulsory to state what is in building products, despite the health risks they may pose, e.g. to indoor air quality.

The two guest lecturers will focus on some of the options offered to environment-committed designers and builders by some natural materials. Their research and design experience shows, among other things, that the use of low-energy building products can be maximised and the use of energy-intensive products can be minimised, without diminishing the living quality of buildings.