The definition of “zero carbon” in the building space is somewhat subjective.  At eTool we have always held the view that any zero carbon claim must be the net result of a life cycle carbon assessment.  Unfortunately many of the industry labels and definitions fall short of this and only capture parts of the life cycle.  Most common and widely adopted in definitions only amount to Net Zero Carbon Operational Energy.  The recognition of Net Zero Carbon Construction commitment is increasing with the higher recognition of embodied impacts and although this is good news for eToolLCD commercially, we would like to see life cycle performance measured which is aligned with our mission to improve the environmental performance of building and infrastructure.  Net Zero Carbon Whole Building Whole Life Cycle is the ultimate goal.  Below we have summarised some of the efforts to define zero carbon.  Despite the varying viewpoints eTool continue to hold fast on the view that the definition of zero carbon is when the life cycle global warming impact of the building is zero (or negative) so reports and/or marketing materials flowing from eToolLCD software will follow this definition.

UKGBC Net-Zero Framework

The UKGBC Net-Zero Framework is a great document for clarifying the definitions of net zero carbon.  Below is an extract which summarises things very well.  There are three main definitions covering “Construction”, “Operations”, and “Whole of Life”.  The details of the whole of life definition are yet to be determined but there certainly seems to be heavy references to EN 15978 in in the naming of the life cycle modules so we would expect to see that standard forming the basis of the Whole Life definition.

eTool were involved in the development of this framework and Pat Hermon ran a webinar summarising the framework which can be viewed below:

Defining Zero Emission Buildings – Review and Recommendations 2011

Although now quite dated, the Australian Sustainable Build Environment Council released this report in 2011 with recommendations on definitions of zero carbon.  They recommended a number of definitions based on the below diagram.  The definitions are summarised as follows:

• Zero carbon building, which includes the ‘building emissions’ shown in Figure ES1
• Zero carbon occupied building, which includes the ‘building emissions’ and ‘occupant emissions’
• Zero carbon embodied, occupied building, which includes the ‘embodied emissions’, ‘building emissions’ and ‘occupant emissions’
• Zero carbon life-cycle, which includes all emissions shown in Figure ES1

Summary Advice

When making a Low Carbon, Zero Carbon or Carbon Neutral claim it’s important to ensure that there’s no risk to your reputation by ensuring you clarify the scope of the claim and make the underlying study public.  Another factor is honouring the intent of the claim.  If the stakeholders intent is to stabilise the climate then it naturally follows that the scope of the study should be “life cycle”.  The other definitions miss significant potential emissions and are unlikely to actually be ensuring a stable climate despite the claim.