Balancing embodied and operational carbon in building envelope design

The material and products used within building facades contribute directly to the embodied carbon of a project. Furthermore, the facade system plays a key role in the regulation of the building’s energy use and associated operational carbon. As a result, today’s facade engineers must balance both the embodied and operational carbon of their design decisions in the pursuit of minimising whole-life carbon. To this end, this article introduces the idea of a ‘carbon payback period’ (CPP) as a metric for assessing the net carbon emissions of design decisions whose scope spans both the embodied and operational carbon. An approach for calculating the CPP is presented, and the need to account for the building performance gap and decarbonisation is highlighted. The article also introduces the concept of the ‘time value of carbon’ with a short discussion on how this may be accounted for within the assessment of the CPP. Note that the CPP should not be used blindly and should inform design decision-making as part of a holistic approach. Engineers should be aware that benefits of climate resilience measures are not quantified in the CPP.