Concrete roof tiles have green credentials

Finding environmentally friendly building materials is not always as straightforward as you might think. There are different ways of looking at the issue.  One way is to consider the energy used in manufacturing a product – its embodied energy.

The purpose of controlling energy use is to reduce emissions of carbon dioxide and other greenhouse gases.

Redland, which has traditionally manufactured both clay and concrete roof tiles, commissioned engineering consultants Ove Arup and Partners Ltd to analyse the carbon dioxide emissions of its operations.

The study was reviewed by independent organisations: the Carbon Trust and the University of Bath.

It looked at the whole manufacturing process – from extracting the raw materials, through transport to the manufacturing plant and through production.

The results, in terms of carbon emissions, confound the school of thinking that automatically assumes natural products such as clay are necessarily more environmentally friendly than concrete.

When looking at manufacturing, the key factor is the firing process: clay tiles must be fired at very high temperatures (around 1,000oC) – an energy intensive process.  In contrast, just adding water and curing at less than 100oC achieves the necessary strength for concrete tiles.  And while the cement used in concrete tiles has high embodied energy, it represents less than 20% of the tile by weight, the remainder being mostly natural materials such as sand and limestone.

The figures in the Arup report show that the embodied energy of concrete tiles at 91-146MJ/m2 is half that of equivalent clay tiles at 240-478MJ/m2, which broadly agrees with previously published independent data.

Redland, as a manufacturer of both clay and concrete tiles, clearly has an interest in understanding the future demand for different material types, and is convinced that reducing the embodied energy and carbon of building materials will be the next major challenge for the sector.

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