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INTRODUCTION

Derwent London has championed the reduction of embodied carbon (EC) in its projects and as a result, now has a reputation as a progressive organisation. This is demonstrated by significant reductions in the amount of EC at several key buildings, such as White Collar Factory (Old Street).

As part of Derwent London’s sustainability programme, mapping and understanding the carbon footprint is a key priority. Through the assessment of several of its buildings, it has amassed knowledge on the most effective ways of reducing EC and has formulated an approach in how its new developments must consider and understand the EC question.

However, in order to reduce EC, there are many challenges around how at buildings level, portfolio level or across the whole of the industry, EC is measured in a consistent way. Another challenge is building the business case for EC and understanding how it can impact on value.

White Collar Factory © Derwent London

UK-GBC CASE STUDY DERWENT LONDON’S ORGANISATIONAL APPROACH TO EMBODIED CARBON

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80 Charlotte Street © Derwent London

Currently, there is no local or national level policy or regulation that requires EC assessment. However, Derwent London is clear that this is an important issue for the organisation and is committing to sustainable urban development which includes low EC buildings.

Derwent London is keen to set the standard for EC and create a marker for industry to follow. As it has familiarised itself with EC through constant measuring and reporting, and learnt what low EC decisions look like and located the intervention points, it has discovered the opportunities and leveraged as many as possible to its advantage. Rather than requiring all Derwent London buildings to be low EC, it has become one more factor to be considered when asset planning and designing. With each iteration, it has become easier to make strategic decisions that can help to lower the final EC figure. Derwent London is now in a position where it can wield EC data at different stages in the building value chain, including investment, planning, design and construction, to its advantage.

Decision-making that includes EC has given rise to lessons in effective concrete mixes including how and when to deploy it, how to texturise it and subsequently, the impact on thermal mass and the operational carbon. Derwent London has also been able to spot similarities across buildings especially in the structural engineering. This is not always a win/win situation in terms of low EC and cost, and there have been trade-offs between low EC wins which have led to a cost uplift. However, by including EC in the range of criteria, the payoff for Derwent London has been getting what they want from their buildings.

DRIVERS

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There is currently not enough knowledge about how swapping out high EC materials and the huge range of building solutions available may affect the EC and the overall whole life carbon of a building. The built environment industry needs to be able to characterise and standardise many more materials and solutions and share information on this issue in order to decrease this risk.

Using a wide ranging materials palette can make EC decision making much more complicated requiring knowledge of one-off solutions. Derwent London has simplified the materials palette which means that it is easier to engage, and understand with the EC agenda.

RISKS

CHALLENGES

Consistency in EC measurement has been a constant challenge for Derwent London. Although industry now has two major standards (BS 15804 for products, BS 15978 for buildings), Derwent London found that each assessment could adhere to the standards, but a different set of assumptions and cut offs would be applied. This was further complicated by the fact that a lot of EC assessments are done on iconic or trophy buildings which can skew the data. Derwent London wanted to drive a universally accepted way of measuring EC in their buildings and developed a brief for EC assessment in order to simplify the process and give clarity to EC assessors. The brief was based on the RICS methodology to calculate embodied carbon and aligned to its development approach. It gives clarity on the markers to be used, boundary conditions, but also the required information points and break downs e.g. structural elements, and material types. This allows comparing like-for-like within the portfolio.

White Collar Factory © Derwent London

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DESIGN STAGE DECISION-MAKING

Even though measurement of EC is essential, the critical part is using the data and changing the decision making process to reflect key intervention points that will affect a building’s EC footprint. EC graphs at the design stage will only ever be snapshots and cannot tell the full story. Using the data to create and inform the next project is key to changing how EC is considered by clients.

From the assessments carried out, Derwent London has found setting the target start point for considering EC at RIBA Stage 2 (concept design stage) and continuing through to Stage 3 (developed design stage) as being the most effective for their approach to development. Undertaking the EC assessment at this early in the design process allows the design team to benchmark the design, and study alternative design options for reducing EC. All too often, EC is considered, at best, too late in the process to be able to change anything or at worst, only as a measurement and reporting exercise.

ADOPTING A WHOLE LIFE CARBON APPROACH

Rating tools such as BREEAM and LEED tend to prioritise operational benefits which, when taking a whole life view, may not impact EC levels. EC can account for a large proportion, anywhere between 30%-60%, of the whole life carbon of a building over the course of its lifetime. This further emphasises the importance of adopting whole life carbon early in the design process i.e. at Stage 2 as well as further decisions taken in Stage 3 and within procurement.

Whole life carbon could also be studied in tandem with whole life costing to further the knowledge around the link between carbon and cost. However, there are far too many variables and the relationship between carbon and cost isn’t always linear. When considering the EC across the whole life cycle of a building, Derwent London takes the approach that there are too many uncertainties beyond a certain point to be able to take meaningful decisions. A practical solution is to draw a boundary around the life cycle in which it is able to influence and control and take EC decisions based on this.

BEYOND DESIGN

Derwent London’s brief is not limited to the design stage and the assessment window continues beyond Stage 3 to capture other aspects. The next stage is to engage the contractors to measure EC through to delivery and Derwent London would like the value chain, both upstream and downstream, to collaborate in reducing EC at every stage.

APPLICATION

Page Street © Der went London

Page Street © Derwent London

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BIG WINS

Throughout the assessments carried out on refurbishment projects, the overwhelming savings made in EC was through retaining existing structures. Derwent London always considers retaining the structure and there is no automatic decision to raze buildings to the ground. This approach has proven to be quicker, cheaper and easier in some cases.

The Page Street refurbishment project retained the existing frame, columns and beams, the substructure, the staircases, the boundary walls and some sprinkler tanks and pipework. Compared to a notional rebuild scenario, Page Street achieves a 48% reduction in whole life carbon emissions. The EC footprint of the refurbishment is 6,650 tCO2e (0.426 tCO2e/m2). The total saving of approximately 15,500 tCO2e is equivalent to the annual energy related carbon emissions of about 3,000 UK households. The cladding of the superstructure and the main frame for an additional floor were responsible for more than 50% of the embodied carbon emissions.

At 80 Charlotte Street, the assessment confirmed that the structure accounts for almost a third of the total EC of the development and a large proportion of this is steel as well as the concrete within the structure and substructure. Concrete and steel offered the greatest potential for improvement. By tweaking the design and procurement decisions relating to steel and concrete, Derwent London can have a direct effect on almost half of the total embodied footprint.

Additionally, by using a “re-skinning” approach using brick gives identity and character back to the area which combined with extra floors and terraces increases the net lettable area (NLA).

Other methods of reducing the EC which Derwent London is now exploring are:

1. Greater resource efficiencies during construction: Examples include reusable formwork and sourcing concrete within 20km. This can also be addressed at early design stages through workshops to identify opportunities for designing out materials and redesigning processes in order to minimising waste. Additionally, during construction, the EC during steel reinforcement is affected by the amount of wastage due to bulk ordering and cutting to size required on site. Transport is also an issue due to the high mass of materials and volume of transport needed.

2. Use of natural and renewable materials: materials that have inherently low EC due to minimal processing

impacts would also be another big win e.g. timber.

3. Use of reclaimed or high recycled content in materials: there are now a variety of products in the marketplace that can be used at different stages of construction that lower the embodied carbon impacts through high recycled content. Rates of recycled content that can be achieved are as follows:

• GGBS in superstructure (50%) and in substructure (50-70%)• 100% recycled aggregate if available locally and 100% steel rebar from distribution centres• Recycled content steel frame (95%)1

• Recycled screed board (50% minimum)• Recycled content of façade aluminium (30%)

4. Circular economy design: Whilst design for 100% deconstruction and reuse is still aspirational, Derwent London can consider how to innovate around this issue and attempt to close loops within its own portfolio.

80 Charlotte Street © Derwent London

1 Specifying recycled steel must also specify the source. In order to maximise the sustainable outcomes, recycled steel should be sourced as locally as possible.

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SHARING DATA

Derwent London is also a supporter of EC industry initiatives and would like to see greater knowledge sharing by other practitioners. All of its EC data is shared on the Embodied Carbon Database, set up by UK-GBC & WRAP and soon to be managed by RICS.

CONCLUSION

Derwent London has started to incorporate EC into its criteria for investing in, designing, planning and constructing buildings to the point where it can now use EC as part of the Derwent London brand. By measuring EC on a variety of projects and using a simpler materials palette, Derwent London has learned the critical intervention points and the structural elements that can be used to lower EC. Additionally, retaining the foundations and structure of an existing building is now one viable approach to lowering EC, increasing the value of the building but also delivering a uniquely Derwent building.

There are many examples of innovations in products as well as processes that Derwent London is exploring to help deliver a low embodied carbon building:

• Identify early the potential for using salvaged materials from the local area from own estate or from local knowledge of the area

• Ensure that risks surrounding using recycled content and higher amounts of reuse are overcome through project insurance

• Contractors during the delivery phase should actively seek to improve on the embodied carbon and recycled content of materials

• Significant reuse of piles• Structural grids that are relatively small with areas at either 6 or 4.5 m, reducing the need for structural steel • Cement substitutes such as PFA and GGBS2 • Biomaterials for insulation• Recycled board for internal divisions• Downcycling

EMBODIED CARBON AND INNOVATION

APPENDIX: PROJECTS ASSESSED

Embodied carbon assessments have been carried out on the following Derwent London properties:

1. White Collar Factory and 2-6 Old Street Yard buildings (Demolition & new build commercial offices)2. Page Street (Refurbishment of commercial offices)3. 80 Charlotte Street & 65/67/69 Whitfield Street (Part new build mixed use, part refurbishment with major

retention of core)

2 Pulverised fuel ash (PFA) and ground granulated blast-furnace slag (GGBS) are cementitious materials that are used to bind concrete together. PFA is a by-product of coal-fired power stations and GGBS is a by-product of iron production. Both can replace some of the cement content of traditional concrete.