“If our global goal is not to release any emissions to the atmosphere, we need to design buildings to be as energy efficient as possible, and to use clean, renewable sources of energy, and stop using fossil fuels,” says Martin Sing, energy and sustainability lead for WSP in Canada.
But, he adds, this only addresses operational carbon emissions. It doesn’t take into account the carbon that’s emitted during the process of constructing a building: extracting the raw materials, processing them and manufacturing building components, transporting all of that to site and assembling it together. This “embodied” carbon has received less attention to date, but it can account for half of the total carbon footprint, and the proportion is rising as buildings become more energy efficient in operation and electricity grids are decarbonized.
“It is technically feasible and realistic to deliver a building that is net-zero in operational terms today, and it’s been done multiple times,” says Sing. “But when it comes to delivering a net-zero embodied carbon building, we're not there right now because the manufacturers of materials aren't there. So that’s where we need to focus our efforts.”
Some of this can be achieved by more material-efficient design, and some by embracing nature-based materials that sequester carbon as they grow, rather than materials derived from or produced using fossil fuels. “On smaller, low-rise building typologies – housing projects up to three or four storeys high, community hubs, visitor centres – you can use timber, bamboo, hempcrete,” says Leversha. “Then you can design them to Passivhaus standards to reduce energy consumption, and use renewables, and they will be net-zero in their build and probably net-zero in operation too.”
For other buildings, there will still be some residual emissions, until we succeed in completely decarbonizing industry, energy networks and transport.