What is embodied carbon?
Embodied carbon is the term used to describe the various greenhouse gases (GHG) emitted to provide the materials to make anything, in our case a building. The various GHG emissions, some nastier than others, are converted to CO2 equivalents, and are usually described as “carbon emissions”. Carbon emissions occur during the life cycle of the material, and Life Cycle Assessments are used quantify all carbon emissions from raw material supply to demolition and disposal.
The carbon emissions from raw material supply (known as Stage A1), to construction (Stage A5), are termed “up-front” emissions, and can represent up to 85% of life-cycle emissions.
The example below is a detailed look at the up-front emissions for structural steel.
Stage A1 - Raw Material Supply: The life-cycle of steel starts in an open-pit iron ore mine, and the source of the carbon emissions is from burning diesel and gasoline in the equipment used.
Stage A2 - Transport: After the iron ore is extracted from the mine, it is transported by truck to a rail line or ocean shipping terminal for transport to a smelter. Carbon is emitted from the fossil fuels used in this stage.
Stage A3 - Manufacturing: The ore is received at a smelter where it is melted in a furnace, poured into billets, and rolled into structural steel shapes. The furnace is heated to 2,500 degrees Fahrenheit, and emits a large portion of the carbon emissions in the manufacturing process. The raw steel is then sent to a fabrication shop for final processing for construction.
Stage A4 - Transport: After fabrication of the steel beams, they are transported to the construction site. This could involve trains, ocean ships, and trucks, and the fuels used in this process are evaluated for carbon emissions.
Stage A5 - Construction: The steel beams are offloaded at the construction site and erected to create the structural frame of the building. The erection equipment uses a mixture of electricity, diesel, and gasoline, all of which are fossil fuels that emit carbon.