Embodied Carbon Emissions: Sustainable Building Materials

Posted by: SusCon

When architect Stephen George and Partners was asked to specify a range of sustainable building materials for an innovative new construction academy in Dartford, Kent, the research it carried out would force it to challenge many long-held preconceptions.

The building was designed for a public/private partnership led by Dartford Borough Council, Prologis and North West Kent College. It is intended to promote excellence in construction skills and learning, the recently opened £5m Sustainable Construction (SusCon) Academy, built by main contractor Winvic Construction, also functions as a demonstration project that incorporates a range of sustainable construction methods and technologies.

Architects Jo Denison and Chris Halligan were keen to justify the materials choices they made for the building, so they examined the green credentials of a range of products. But here they ran into a problem that is likely to dominate the green agenda in the coming years, namely how are those sustainable credentials to be calculated? As we illustrate here and overleaf, that question resulted in some surprising choices at the academy.

Sustainable talk today is all about reducing embodied carbon, that is, a product’s impact on the atmosphere in terms of CO2 emissions generated during the manufacture, transport and construction of its various materials. But as the Stephen George team’s research intensified, they found a lack of consensus on exactly how embodied carbon was defined and calculated.

“Trawling through all the technical literature was extremely time consuming,” says Denison. “It’s a minefield out there, every manufacturer wants to be perceived as being green and will grasp at any vague evidence to gain that accolade.”

Denison and Halligan found some products that were not marketed as sustainable had, in fact, very low embodied carbon, such as concrete blocks, which can include 80% recycled content. Aluminium is often considered to have high embodied carbon because it is energy intensive to produce, but the team found it is also highly recyclable, possibly making it a viable sustainable option.

“It’s really difficult when you’re writing a specification to know where the a product will come from and its recycled content,” adds Halligan. The team also realised that knowing a figure for embodied carbon did not give the whole picture, as a product might still be toxic to humans or the environment or have no options for recycling.

Confused by these findings, the gaps in the available knowledge and a lack of effective guidance on the right specification choices to make, Stephen George opted to draw up its own, personalised materials selection criteria.

The architect’s dilemma is typical of many practitioners struggling to make sense of a shifting environmental landscape. Although the industry has become very efficient at cutting the operational carbon emissions of new buildings, through a combination of efficient design, renewable energy sources and carbon offsetting, the science of measuring and reducing the impact of embodied carbon is still in its infancy. That situation is about to change.

As operational emissions reduce, the embodied carbon component of a building’s total carbon footprint increases. The RICS carbon profiling tool Redefining Zero, developed by Sturgis Consultants, has calculated the embodied carbon component of a supermarket as 20% of its lifetime carbon footprint, and that of a house is around 30%. But by 2019, when all new buildings must have zero emissions, embodied carbon will account for 100% of the total footprint.

In Europe new legislation is set to bring embodied carbon to the top of the green agenda. European Directive CEN TC 350 will require member states to legislate so that all new buildings are designed from a whole-life perspective, which takes into account both operational and embodied carbon emissions. As such, designers will have to complete whole-life assessments, which take into account emissions associated with the production of all materials used in a building’s construction, including their manufacture, transport to site, and possibly also their subsequent maintenance and end of life disposal or recycling.

The UK government’s Innovation and Growth Team acted on this in November, calling on the Treasury to introduce into its Green Book a requirement to conduct whole-life carbon appraisals, which will also require the creation of a standard method of measuring embodied carbon.

But arriving at a standard definition of what embodied carbon is and how it should be measured is a huge challenge. Quantity surveyors already offer basic embodied carbon assessments as an extension to cost and lifecycle assessments, but a more complex assessment methodology will require a greater understanding of material and resource inputs into construction, says John Connaughton, head of sustainability at Davis Langdon.

“Understanding what goes into a building might seem obvious but the way QS’s typically measure things is not amenable to assessing their environmental impact,” says Connaughton. “Many of our calculations are based on floor areas or volumes, but assessing the impact of a concrete floor, for example, means knowing the mass of concrete going in, the relative concrete mix in terms of amounts of sand, aggregates and water, the amount of reinforcement etc. There’s a measurement problem, which can be resolved, but someone has to work it all out.”

Composite products, such as mechanical and electrical systems like boilers or air conditioning units, are particularly problematic due to a lack of product-specific embodied carbon data. A boiler, for example, is made up of steel, aluminium, cast iron, PVC and other materials, but estimating their weight and relative embodied carbon is impossible without taking it apart.

There is also the issue of what limitations are set on an embodied carbon assessment. Material-related emissions are obviously important, but should it also include waste generated during construction, energy used to demolish the building, or energy used to maintain or replace products? It is difficult at design stage to estimate values for any of these.

Using Building Information Modelling (BIM) software, it may one day be possible to model the embodied carbon of every single component in a structure. “That level of detail is probably unnecessary,” says Adam MacTavish, director of sustainability at Cyril Sweett. “All the work done to date shows embodied carbon is dominated by a dozen or so key materials and components, mainly structural items and frequently replaced products like carpets and M&E systems. Rather than get bogged down in data, it’s better to make standard reference assumptions and have default values for things like walls, ironmongery, security systems etc.”

To help resolve these issues, the government’s Technology Strategy Board has allocated more than £4m to 14 consortia to aid innovation in design and decision tools for low impact buildings. Consultant Faithful + Gould is working on development of the Integrated Material Profile and Costing Tool (IMPACT), a software plug-in designed to prioritise low embodied impacts and cost-effective design over the whole life of a building.

Meanwhile, Cyril Sweett has teamed up with architects, M&E and software engineers to develop Project Rapier, which will use early stage design data
to generate a 3D model of a building, attribute it with rough specification data and use that to calculate whole-life costs, plus determine and help reduce embodied and operational carbon.

But whether these tools can generate meaningful and comparable results will depend on the accuracy of raw embodied carbon data for the various materials.

At present this data is produced by third party manufacturers and research organisations, which have varied interpretations and definitions in terms
of what information they include. A “cradle to gate” figure will include all the carbon produced until a product leaves the factory gate; a “cradle to site” figure includes all of the carbon emitted until the product has reached the building site, including the impact of transport; while a “cradle to grave” figure accounts for all of these factors, plus the product’s eventual disposal or recycling at the end if its life.

Embodied carbon figures for different materials can vary greatly depending on which methodology is chosen to assess them. For example, under a cradle to gate analysis timber performs well due to the relatively low energy used to extract and manufacture it. But under a cradle to grave analysis, it performs poorly as a high percentage of the material tends to go to landfill.

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Information Updated on: 5 July 2011