Circular Economy (CE) is a philosophy that has gained a good deal of momentum within sustainable construction recently.  We have seen the new draft London Plan requiring consideration of Circular Economy (as well as embodied carbon) on all major London developments.  eTool also recently contributed to the UKGBC guidance on Circular Economy (a copy can be viewed here) and there is a definite feeling of ground-shift within the industry which is exciting to see.

The key concept behind building circular is that waste is simply a design flaw and that if we can remove it entirely then we will see improvements to the environmental, cost and social performance of our projects.

A circular economy is a global economic model that decouples economic growth and development from the consumption of finite resources. It is restorative by design, and aims to keep products, components and materials at their highest utility and value, at all times (Ellen MacArthur Foundation)

Many aspects of circular principles currently have a qualitative focus.  A quantitative approach, however, can go hand-in-hand with this through LCA. By analysing the environmental and/or economic impacts of the potential circular strategies over the life cycle we can prioritise those that provide the greatest benefit.  There is a lot more that can be drawn from an LCA study than embodied carbon data.

In eTool we measure full impacts over the building life cycle from cradle-cradle and have numerous other environmental indicators that help measure environmental performance beyond Embodied Carbon and life cycle GWP.  One group of indicators now measured in eTool LCAs has been developed by HS2 to help quantify circular principles, see materials efficiency metrics for further details.

Quantifying Benefits

There are numerous circular principles that may produce good environmental outcomes.

• Refurbishing/repurposing/recovering existing buildings or materials
• Specifying materials with high recycled content
• Designing for disassembly and end-of-life reuse
• Designing for longevity/adaptability/reusability where its appropriate.

However, without full life cycle quantification of the strategies under consideration, there is no way of knowing the relative benefits, which ones to prioritise and which ones produce perverse outcomes. For example, recycled aggregate trucked from 70km away actually has much higher impacts today than locally sourced virgin aggregate.

Global Warming Potential (kgCO2e) for product and transport stage (A1-A4)

Recycled metals, on the other hand, have relatively minor transport impacts (see figure below). eToolLCD contains a growing list of “Recommendation” strategies that users can apply to their LCA work.  We have a tagging system with a new “circular economy” tag for any that relate to refurbish/recycling/deconstruction/longevity.

Module D

Module D of EN15978 relates to “benefits and loads beyond the system boundary” and has particular relevance for circular strategies,

• D1 – Operational Energy Exports
• D2 – Closed Loop Recycling
• D3 – Open Loop Recycling
• D4 – Materials Energy recovery
• D5 – Direct Re-use

Under Module D where materials will be recycled at the end of their life, a benefit credit is given in the LCA. For example, if a cladding system is designed for deconstruction the materials are more likely to be recycled at the end of life we will see an improved performance in the LCA from module D (product reuse).

1 Tonne of Virgin aluminium shipped 1500km

Allocating recycling loads and benefits can get a little tricky when trying to avoid any double counting of impacts, more information on Module D can be found at this blog post.

Longevity and functional units

Buildings that can last for very long periods are clearly a better use of resources than buildings that get knocked down after 20 years.  The life expectancy of many low-density inner-city commercial buildings is unlikely to reach far beyond 20 years due to redevelopment pressure. However certain high-density megastructures (such as the Shard) will likely still be standing for 100 years or more.  Its going to be a long time before someone thinks they can replace the Shard with a building that will create more value from the real estate. To capture the relative benefits and savings of a buildings life expectancy it is important to apply an appropriate functional unit to the LCA. It is common in the industry to measure impacts in absolute terms over a 60 year period – kg CO2e/m2.  Applying a realistic life expectancy based on building location and density relative to its surroundings and presenting impacts in temporal terms – kg CO2e/m2/year the LCA will present a truer picture of the results.  This is particularly important when considering Circular Economy principles.  Materials going into a building that lasts twice as long before being demolished and sent to landfill will have half the life cycle impacts.

Circular Economy Philosophy

Whilst there are often clear quantifiable benefits of applying circular principles it is important that we do not lose sight of the bigger picture. It makes sense to rely purely on circular economy principles when trying to reduce finite resource exploitation, however, many building materials today actually have an abundance of supply – see our “Are we running out of materials blog post”. When we are trying to optimise for a different environmental problem, for example, Global Warming, purely focussing on the circular economy principles may not necessarily result in a net positive outcome (as shown above).

Circular economy represents one of the many “means” to the end goal of true environmental sustainability. We must be careful to quantify our strategies and avoid applying circularity simply for the sake of circularity which may sometimes be more detrimental to the planet than a linear strategy. We will need tools such as recycling and re-use to achieve a zero carbon future but material consumption is not in itself always a bad thing if done sustainably relative to the alternatives.