Rebuild or retrofit:
the environmental case
HOW SHOULD THE PRINCIPALS OF CIRCULAR ECONOMY AND WHOLE LIFE CARBON INFLUENCE OUR DECISIONS ON HOW WE IMPROVE RETAIL ASSETS?
WHOLE LIFE CARBON – THE BASICS
Traditionally, the property industry has measured the performance of buildings using compliance tools, such as Energy Performance Certificates (EPCs), because they’ve been the most widely understood and accessible metric, and the industry standard for comparison. The industry has focussed on understanding and reducing the operational carbon and cost without looking at reducing material use at the same time. Moving towards a zero-carbon future has clarified our thinking on different metrics and methodologies. The industry now looks at how buildings are made, how they are operated, and how they can be re-used before their disposal.
This is where Whole Life-Cycle Carbon (WLC) emissions fall into place as WLC provides a true picture of a building’s carbon impact on the environment. WLC emissions are operational and embodied emissions over a building’s entire lifecycle. Embodied carbon is the amount of carbon emitted during the construction, use, and end of life stages of a building, e.g. the extraction of raw materials, the manufacturing and refinement of materials, transportation, installation, and the use of a building over its entire life, including its demolition and disposal. Operational carbon is the amount of carbon emitted once a building is in use. Real estate is responsible for 39% of annual carbon emissions – operational emissions account for 28% and the remaining 11% is attributed to embodied carbon of new construction; or to put it another way embodied carbon accounts for almost 30% of property emissions.
Although both the refurbishment of existing buildings and the construction of new ones have the potential to significantly improve the life cycle impact of buildings, it’s not always a clear-cut choice between the two options. And this is applicable to any type of use, i.e. office, retail etc.
THE BENEFITS OF REUSE
When is it better to reuse and when is it better to redevelop? A major refurbishment can reduce operational carbon emissions considerably by upgrading the fabric and providing equivalent building services to newly built standards. At the same time, it can cut embodied carbon emissions significantly because a big part of the embodied carbon emissions of a new build are associated with elements such as the sub structure, upper floors, roof, and frame, which should be retained at a major refurbishment.
On the other hand, new buildings have a better potential for improving operational efficiency as the result of better design and less constraints, i.e. form factor, window-to-wall ratio, passive design measures, energy efficiency measures etc., while new standards and tools can reduce the embodied carbon emissions.
Carrying out a WLC assessment can be used as a tool for assessing the carbon impacts of design options, alongside other factors such as cost, to select which one is more carbon efficient. For instance, measuring the upfront carbon at each stage of the construction will involve breaking a building down into its elemental parts and applying carbon emission factors to the quantities of each element. Take, for example, a building’s superstructure: a conventional frame would result in emissions of 500 kgCO2 e/m2, with a frame that includes timber would result in 350 kgCO2 e/m2, providing significant savings. Following such a methodology, one can assess whether a refurbishment or a replacement is the more environmentally and economically responsible option.
A WLC study for a new build 320,000 sqft shopping centre in Hampshire, produced by Sturgis compared three scenarios over a 60-year period: