Changing the materials we use to build our houses and commercial buildings can help us reduce emissions

There are two main avenues of exploration. Either we reduce - or eliminate - the emissions associated with existing materials, or we use different materials. Such alternative materials can be either carbon reducing or carbon negative.

Between them, steel and cement production account for about 8-10% of global carbon emissions. Both industries are expected to grow significantly over the coming decades in line with rapid urbanisation.

  • Traditional steel fabrication emissions come from the energy used in the furnaces but also because carbon (usually in the form of coke, derived from coal) is used as a reductant to remove the oxygen from the iron ore. To achieve low (or zero) carbon steel an alternative reductant has to be found: one alternative is hydrogen, another is electrolytic steelmaking - transforming steel through electrolysis.

  • Cement is the primary ingredient in concrete. Like steelmaking, cement production releases greenhouse gas emissions both directly - through the calcination of limestone to produce calcium oxide and CO2, accounting for 60-70% of its emissions - and indirectly from the fossil fuels used to heat the kiln. Indirect emissions can be reduced through reducing the temperatures required, decarbonising the fuel supply and capturing / storing the carbon produced.

  • When it comes to direct emissions from cement production, there are two forces at work. Carbon dioxide is released in cement manufacture but from this point on cement naturally sequesters CO2 from the atmosphere in a process called carbonation. Carbonation rates vary. One solution in this area is to reduce the limestone used as an input. Another is to increase the volumes of CO2 absorbed in carbonation by exposing cement to concentrated CO2. An even more ambitious approach seeks to make cement a negative carbon product by curing the cement with alternative materials which may allow more than one carbon atom to bond with each calcium atom.

Another way in which buildings can become carbon sinks is if they are built of wood (or other organic materials, including hemp and straw), not cement and steel. Producing engineered timber construction materials is a much less carbon intensive activity than producing steel and cement. Additionally, wood is itself a carbon store. It is estimated that timber products lock approximately 1 tonne of CO2 per 1 m3 of wood.