With sustainability and ESG considerations increasingly driving the agendas of developers, investors, finance, pension funds and many occupiers, the question of whether to refurbish existing stock or to demolish and rebuild entirely is not an easy one. The difficulty in these decisions can be seen with M&S's controversial recent proposals to demolish their Oxford Street premises and rebuild which was backed by Westminster City Council and the Greater London Authority but subsequently called in by the Secretary of State.

There is of course an inherent contradiction in construction of new buildings. If designed and built to a high standard, new buildings have far superior environmental operating performance and energy efficiency and lower running costs than older building stock. However at the same time, they need a huge investment of carbon in the materials and processes used to build them and can be expensive in terms of the carbon lost in the form of the embodied carbon within any existing buildings which are demolished.

The rush to achieving operational excellence of buildings is no longer a headlong rush to build new though, retrofitting and refurbishing assets has been gaining significant momentum. The circular economy is gaining ground in the construction industry with the reuse and repurposing of building materials and works on site which can lead to significant reductions in carbon emissions when compared to a new build.

The choice is not simple. While the most environmentally friendly construction option is often to retrofit existing buildings using sustainable materials and maximising energy efficiency, there has been much debate about whether that can achieve the same standards as a new build designed with energy efficiency at the heart of all aspects and to incorporate new technologies. Clearly it is more difficult to work within the constraints of an existing structure than with a blank page which can be designed more freely to produce exactly whatever type of space a developer wishes to create. Some have questioned if retrofitting can achieve future proofing within the confines of an existing structure and have as long a life cycle as a new building constructed of more modern and in some cases superior materials.

The lifecycle of the building is important and key when assessing the potential for losing or breaking even in terms of embodied carbon. If the building lifecycle is sufficiently long, the carbon efficiency in operation will counteract the loss of embodied carbon in demolished structures. On the other hand, where buildings have short life cycles and require to be demolished entirely and replaced with entirely new buildings, large amounts of embodied carbon which have already been spent are potentially lost.

It is critical to look at the whole of life carbon footprint of the buildings but design and material choice also plays a part in this, where buildings are designed to allow them to be repurposed more easily and to allow flexibility and adaptability in future use. A move to this long term thinking approach is the key.

Ultimately, there is no "right" answer here. The views are often polarised and whilst carbon is a key consideration, it is not the only sustainability consideration: health and wellbeing, biodiversity, climate resilience and social value should also be considered. There is a clear direction of travel here though from the Government who have committed to looking at embodied carbon as part of their Net Zero strategy. It seems likely therefore that it will only be a matter of time before reporting on embodied carbon and seeking to set standards for new construction comes forward in some form. And, while a number of organisations are ahead of the game and have already been actively looking at or incorporating this as part of their own reporting and metrics, it may become mandatory and not optional for all.