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Sustainable Construction Materials

The American Association for the Advancement of Science (AAAS) met last week to discuss lowering carbon emissions by erecting skyscrapers, amongst other buildings, out of wood.

Populations of cities are expected to continue to rise but buildings constructed from steel and concrete, two of the most common building materials, generates around 8% of the world’s man-made carbon-dioxide emissions. If cities are to expand and become greener at the same time, they will have to be made from something else, reports The Economist.

Wood is one of the most promising sustainable alternatives to steel and concrete. Not every day wood, it's a material called engineered timber that's exciting architects. This is a composite of different layers, each designed to meet the requirements of specific components such as floors, panels, cross-braces and beams. Besides engineering the shape of a component, designers can align the grains in the layers to provide levels of strength that rival steel, in a product that is up to 80% lighter.

Engineered timber is, moreover, usually prefabricated into large sections of a building in a factory. That cuts down on the number of deliveries that have to be made to a construction site.

All this makes a big difference to carbon-dioxide emissions. Michael Ramage of Cambridge University told those assembled at the AAAS meeting of a 300-square-metre four-storey wooden building constructed in that city. Erecting this generated 126 tonnes of CO2. Had it been made with concrete the tally would have risen to 310 tonnes. If steel had been used, emissions would have topped 498 tonnes. Indeed, from one point of view, this building might actually be viewed as “carbon negative”. When trees grow they lock carbon up in their wood - in this case the equivalent of 540 tonnes of CO2. Preserved in Cambridge rather than recycled by beetles, fungi and bacteria, that carbon represents a long-term subtraction of CO2 from the atmosphere.

The current record for the world's tallest wooden building is held by the 85-metre-tall Mjostarnet building in Norway (see picture), completed in 2019. But this may soon be dwarfed by the River Beech Tower, a 228-metre edifice proposed for a site beside the river in Chicago.

If building with wood really does begin to take off, will there be enough trees? With sustainably managed forests that should not be a problem, says Dr Ramage. A family-sized apartment requires about 30 cubic metres of timber, and he estimates Europe’s sustainable forests alone grow that amount every seven seconds. Nor is fire a risk, for engineered timber does not burn easily. According to a report by the Potsdam Institute for Climate Impact Research, in Germany, large structural timbers are fire resistant because their inner cores are protected by a charring layer if burnt. It is therefore hard for a fire to destroy them.

All in all, then, it looks as if wood as a building material may get a new lease of life.


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