Why cutting operational carbon is the priority

The Green Construction Board’s Low Carbon Routemap model shows that in 2010 operational carbon represented around 80% of the built environment’s emissions, with embodied or “capital” carbon representing a further 18%. The model shows a trajectory where capital carbon comes to represent nearly 40% of the built environment’s emissions by 2050. The required reduction in operational emissions, and the relative increased importance of embodied, demands zero-carbon new build in line with current proposed timelines, as well as decarbonisation of the grid, and the Routemap shows how meeting 2050 targets will require 95% of easy to treat homes and 70% of hard to treat homes to be retrofitted with “insulation, draughtproofing and superglazing”.

Given slow progress on energy efficient retrofit these targets look ever more challenging – but are now enshrined in the UK construction strategy within the aim of 50% greenhouse gas reduction by 2025. In the face of other potentially competing construction strategy targets (cost and time reductions) some in the industry have leapt to recommending, for example, that operational energy improvements should be shelved in favour of a focus on embodied or capital carbon.

It is unlikely that a reliable methodology for assessing the whole life emissions of building components and products can be required in regulation before 2019

Of course, when operating energy is effectively minimised, embodied energy will become a large part of the remaining problem (as the Routemap clearly shows). However, I would argue that energy demand reduction is the priority and the calculation of the embodied energy of a building, and its whole life implications, is neither straightforward nor ready to be applied across the board, especially since an increasing number of products are imported. In a recent report on the UK carbon footprint, the Climate Change Committee considered that there is “a high degree of uncertainty around (non-EU) emissions given different methodologies, data sources and gaps”, and they quote an example showing how embodied emissions of insulation for a typical house are far outweighed by the whole life operational carbon saved (at a 1:35 ratio!), concluding that solid wall insulation therefore saves significantly more emissions than are produced during manufacture and installation.  

Although some have suggested that embodied carbon should be included in the zero-carbon definition for 2019, I believe that it is unlikely that a reliable methodology for assessing the whole life emissions of building components and products can be required in regulation before 2019. In the meantime, designers can do a great deal to minimize embodied carbon by understanding how building form and massing can influence energy usage. Inefficient building forms, and excessive use of the high-embodied structural elements, will struggle to meet Near Zero Energy standards, and rationalised forms result not only in less surface area (and therefore less heat loss), but also, as a consequence, less building material and thus less embodied energy and cost. The WRAP Embodied Carbon database, due to be launched this spring, will expand our knowledge of embodied energy and provide benchmarks for different building typologies, but (as with the Green Guide) will largely be based on generic product values which can vary significantly from one manufacturer to another. Moving from those values to project-specific data requires investment from the manufacturer which to date has produced only a handful of detailed Environmental Product Declarations on a voluntary disclosure basis.

Lynne Sullivan is a founding partner of Sustainable By Design