Embodied energy: The next big carbon challenge

The industry has got very good at creating low-energy buildings in a surprisingly short space of time. This move has been aided by increasingly tough Building Regulations and planning requirements, and a growing awareness of the need to be more friendly to the environment. There is a multitude of tools and technologies out there to help reduce energy in practice, but there is still one carbon challenge left for designers to get stuck into: how to reduce the energy embodied in building materials.

Embodied carbon is rising up the sustainability agenda, partly as a result of Emerging Findings report from Paul Morrell, the chief construction adviser, which was published in March. This contains 18 recommendations on how to reduce the UK’s carbon emissions, including by measuring and accounting for embodied carbon. Crucially, he recommends this should be incorporated into the Green Book, the Treasury bible for public sector procurement. This has created a flurry of activity including the recent launch of a RICS tool called “redefining zero”, which aims to help designers cut embodied carbon. A recent UK Green Building Council seminar on the topic was massively oversubscribed, and when the latest revisions to Part L takes effect in October, embodied carbon will form a bigger proportion of a building’s carbon lifetime footprint than at present. To help you get to grips with this trend we have prepared a handy guide to what it means for you.

What exactly is embodied carbon?

Good question. On the face of it the answer is straightforward: it is the energy used to make the cement, steel, aluminium and all the other materials used in a building. In reality, it is much more complicated than that. For example, a concrete block sourced from a factory just down the road will contain less embodied carbon than one from China because of the energy used to transport it. Your shiny aluminium window might contain relatively little embodied carbon because it is made from recycled materials. Or maybe it comes from virgin aluminium made using hydroelectricity rather than carbon-intensive coal. Embodied carbon also includes emissions from the contractors’ operations, ranging from their excavators and cranes to boiling the kettle for all those cups of tea.

By 2019, embodied carbon will make up 100% of a building’s carbon footprint

How much embodied carbon does my building contain?

Depending on the building type, it can be a lot. For example, distribution warehouses don’t use much energy for heating and lighting, which means the embodied carbon component of the building’s total carbon footprint is high. Sturgis Associates developed the RICS tool and calculated that the embodied carbon in a distribution warehouse was 60% of its total lifetime carbon footprint, whereas a supermarket, which uses lots of energy, has an embodied carbon content of 20%; a house has something like 30%.

Does embodied carbon matter?

If the figures above aren’t enough to convince you, consider this. The closer we get to zero carbon buildings, the bigger the percentage that embodied carbon contributes to the total carbon footprint. So by 2019 embodied carbon will make up 100% of a building’s footprint. Given its determination to make all buildings zero carbon in nine years, someone somewhere in government is going to notice this - and do something about it.

Does this mean all buildings will eventually be made from wood, old wine bottles and thatch?

That’s unlikely. The key issue is the overall carbon impact of the material during its lifetime. So a high embodied energy product such as a brick might have a lower overall impact than timber cladding because it lasts hundreds of years. The RICS’ tool allocates building elements a lifetime - so, for example, a structure might allocated a lifetime of 75 years, high performance cladding 40 years and central plant 20 years. It would take a heavy-handed regulator to control emissions on the basis of embodied energy alone, as only by factoring in lifespan can the overall carbon footprint, or embodied carbon efficiency of materials be calculated.

How is the whole-life carbon footprint of a building measured?

The theory behind this is simple. You do the standard Part L calculations to find out how much energy the building will use. The embodied carbon efficiency of materials is also calculated, including how many times these will be replaced over a building’s lifetime. Combine the two and you get the carbon footprint of the building.

There are established tools for measuring operational carbon, but what about the embodied bit?

There is the newly launched RICS tool, and there are established sustainability consultants such as Dcarbon8 that specialise in carbon profiling. The Technology Strategy Board is funding the development of several programs that will calculate the carbon footprint of buildings. For example, software specialist IES, BRE, Faithful + Gould, the Construction Products Association, Willmott Dixon and consultant AEC3 are collaborating on a tool called Impact. This is designed to plug into existing CAD systems to show the embodied energy content of materials in a design. This will be available with the IES dynamic thermal modelling tool from 2011 and as a plug-in for other software from 2012.

Another tool is being developed by building defects insurer BLP with Cambridge university. BLP has a comprehensive database showing how long products last and has already used this to develop a tool enabling housebuilders to calculate the lifecycle costs of homes. They are extending this so it will be able to also calculate embodied and operational energy and carbon too. A version for new homes will be available in a year and a second version for existing homes a year later. The idea behind both tools is that users will be able to adjust one building element and each tool will automatically calculate the impacts elsewhere.

Will the results from these different tools be comparable?

This is where things get really complicated. All these tools calculate the carbon footprint of buildings, but rely on third party data for the embodied carbon of materials. Bath University has published a database for the embodied carbon content of construction materials which is used by many people including the RICS.

Unfortunately this data is very generic and isn’t product specific. As carbon profiling gets more sophisticated, the ultimate goal should be robust data that allows specifiers to choose an aluminium window over an identical but rival product on the basis of embodied carbon data. This means getting product manufacturers to agree on one standardised way of measuring this. This is a tall order which can be illustrated by the following example. The embodied energy content of concrete can be considerably reduced by substituting cement for ground granulated blast furnace slag. Where does this stuff come from? It comes from the kilns of the concrete lobby’s arch enemies the steel industry and is the byproduct of an energy-intensive process. So does the steel industry suffer an embodied carbon penalty for the energy used to smelt steel that is given for free to the concrete people in the form of GGBS? Or can the steel people claim some carbon brownie points by saying the embodied energy content of that GGBS should be offloaded onto the concrete people making steel look greener but concrete a darker shade of grey? Getting agreement here is a task on a par with finding lasting peace in the Middle East.

Is there any hope for a common carbon metric?

Salvation could come in the form of CEN TC350. This is a technical committee of the committee for European norms who are busily preparing a suite of European Standards covering the sustainability of buildings. This includes standards for measuring embodied carbon and the lifecycle of components and tie in with the ones available from the International Standards Organisation. When these standards are ready they won’t be compulsory, but they will provide a common metric across Europe and crucially should anyone decide to regulate embodied energy they are obliged under European law to use European standards. Those with an eye to the future are embracing CEN 350. For example, BBA has just launched environmental profile certification. This measures 13 environmental impacts, and BBA says it will ensure it aligns with the principles of CEN 30.

Given that embodied carbon is rapidly catching up with operational energy as a concern, some form of regulation is inevitable

Does this mean embodied energy will be regulated soon?

Given that Paul Morrell has called for embodied carbon to be incorporated into the Green Book, and that it is rapidly catching up with operational energy as a concern, some form of regulation is inevitable. On a very basic level, the embodied carbon efficiency of materials could be incorporated into building regulations with maximum limits. Alternatively, Part L could be extended so it included the embodied efficiency of materials with a maximum whole life carbon emissions target. Another possibility is to allocate buildings a carbon valuation. If a developer wanted to knock down a building, they would have to take into account the carbon value of the building they were demolishing as well as the new development. Ultimately, this could be taxed or regulated, which would make people think twice about demolishing useful buildings and minimising the carbon footprint of replacements. The industry might think the roadmap to zero carbon is clearly marked out but be prepared for a major diversion on the way.

What British Land is doing about embodied carbon

British Land prided itself on the low carbon emissions of its new developments but like most of the industry had little idea of how much carbon was embodied in these buildings. To find out it commissioned sustainability consultant Dcarbon8 and Sturgis Carbon Profiling, which put together the RICS tool, to work out the lifetime emissions of its low-energy Ropemaker Place office.

Based on Part L calculations for energy use, it found that more than the lifetime of the building embodied carbon represented 42% of emissions and operational carbon 58%. Sarah Cary, British Land’s sustainable developments executive, wasn’t surprised by this, as Dcarbon8 had said this was typical of new office buildings. However, her eyebrows rose when she worked out British Land’s total emissions for the last two years. In 2008-09, the embodied carbon from its new developments was the same as all its operational emissions, which includes energy used by tenants. In 2009-10, a quieter development year, embodied carbon emissions were still 50% of its operational emissions. “It says to me as a company we have to learn from this and see how we can manage and reduce these emissions,” says Cary.

What will British Land do differently on its next project now it is armed with this knowledge? “It doesn’t mean drastic behavioural change but it does mean we will have to be much more careful about what materials we use in the future,” says Cary.

The first stage is more thorough monitoring - for example, contractor Mace, which built Ropemaker Place, wasn’t sure about the percentage of cement replacement used on the project. Next time round, Cary will expect the structural engineer and contractor to work out the optimum amount of cement replacement that can be used. Reusing materials from buildings that are being demolished is something Cary would consider too. Making sure these were up to the job would be the responsibility of the contractor. “We would have to get the materials tested and there would be a cost implication with that,” she says. “We might be making contractors very unhappy saying that,” she adds, pointing out that clients and developers need to take the lead to drive change through the industry.

Other changes include making sure all the components in a system have a similar life. Cary cites an example of a nearby building where the cladding life expectancy was dictated by the life of the fixings, which failed before the rest of the system. Roofing materials and sealants have comparatively short lives, which is something Cary says needs looking at to see if there are longer-living alternatives. Cary stresses there is a long way to go with reducing embodied carbon. Ultimately, and assuming the performance was identical, she would like to choose materials based on embodied carbon content. “I would like more robust data on different materials so I have enough information to make a choice between different systems,” she says. “What you really need is an industry standard for individual products.”

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