In construction, ‘net zero carbon’ means that a building’s carbon emissions are zero, or even negative. It does not necessarily relate to emissions of carbon dioxide only. The impact of other greenhouse gases (such as methane) is measured as a carbon equivalent, so ‘carbon emissions’ can refer to all greenhouse gases.
The UK Green Building Council (UKGBC) defines net zero in construction as, “When the amount of carbon emissions associated with a building's embodied and operational impacts over the life of the building, including its disposal, are zero or negative.” This is ‘whole life’ net zero carbon, but there are alternative definitions.
Whole life carbon as defined by the UKGBC comprises two different types of carbon: operational carbon and embodied carbon.
Operational carbon, as the name suggests, is the carbon emissions that result from the building’s use. This includes regulated emissions, which are controlled by the Building Regulations and are associated with, among others, a building’s heating and hot water systems.
It also includes unregulated emissions, which result from the activities of the building users. Unregulated emissions are not accounted for in compliance calculations.
Embodied carbon includes emissions due to the production and transport of building materials, the processes on site during construction, and the way in which components are reused, recycled, or demolished at the end of a building’s life.
For a given construction project, ‘net zero carbon’ could mean the reduction of any of these types of emissions to zero.
For some buildings, it might only be viable to address regulated emissions. On other projects it might be possible or desirable to look at whole life carbon, addressing emissions across the building’s complete lifecycle.
The key is to establish what net zero carbon means for the specific project from the earliest possible stage of the process. If the definition is made and understood during the preliminary design stages, it can inform all the decisions that come after and save time and money.
The alternative is to set the definition at a later stage and then overhaul the design and specification because net zero carbon was never accounted for in the first place.