Embodied Carbon Strategies

Materials and components that are likely to have high embodied carbon contributions include the following:

• CEM1 cement (100% Portland cement)
• Steel sections and re-bar
• Aluminium
• Synthetic carpets
• Raised access floor systems
• Galvanized steel services such as electrical containment and ductwork

In general, designers should aim to design to minimise quantity, whilst providing high levels of functionality, robustness and flexibility. Designers should avoid oversizing components and find creative, beautiful ways to design out components all together. For example, making use of exposed structure to not require ceilings or linings at all.

Simple architectural forms tend to require less material resulting in lower embodied carbon emissions. A good indicator of form complexity is the heat loss form factor, which is the ratio of building envelope area (including below ground elements) to the internal floor area. Form factors of 2 or less are good for heat conservation, limiting embodied carbon and probably limiting cost too.

Structural frames and other load bearing structures should be designed to be as efficient as possible. Consideration should be given to limiting spans (for example by reducing column spacing) so that the thicknesses of spanning elements can be minimised.

Building services designers should also design to minimise quantity. Potential strategies could include making the most passive design to limit plant size or not need it at all, avoiding convoluted service routes and/or using surface mounted cabling, rather than containment systems.

These types of quantity minimisation strategies should be done as a priority and in conjunction with choosing materials with low embodied carbon rates.

Concrete and cement
To reduce the impact of concrete and other products using cement (such as blocks) it is essential to reduce the quantity of CEM1 and make use of blended mixes with proportions of low carbon cement replacements such as ground granulated blast-furnace slag (GGBS) and fly ash. However, these substitutes are by-products of steel manufacturing and coal-burning, as a result, their true environmental impact is often brought into question. Furthermore, as these industries are likely to decline in a low carbon future, GGBS and fly-ash are likely to become unavailable. Designers will need to look to alternative low carbon cement replacements (such as limestone fines) in the near future.

Steel
Virgin steel made in a basic oxygen furnace (BOF) from iron ore incurs embodied equivalent carbon dioxide emissions of around 2800 kgCO₂e/tonne. Whereas steel made from 95% scrap in an electric arc furnace results in much lower embodied emissions, around four times less, approximately 800 kgCO₂e/tonne. Furthermore, electric arc furnaces can be powered from low carbon electricity further reducing the embodied carbon of the steel produced from scrap. Therefore, making use of steel products with >90% recycled (scrap) content is a way to minimise the embodied carbon of steel on a particular project (the word “particular” here is relevant and we’ll come back to that in a moment).

There are several UK manufacturers/suppliers who can supply steel re-bar with EPDs stating >95% recycled content and embodied carbon rates < 800 kgCO₂e/tonne. Designers and contractors could consider the feasibility of procuring re-bar from specific suppliers certified under specific EPDs. However, there is a catch. Whilst making use of large proportions of scrap steel can lead to low carbon steel for a particular project (or country), the global quantity of scrap steel is limited. Globally, scrap steel can only meet around 40% of production. If one project (or country) uses all the scrap steel, then other projects (or countries) won’t have access to that low carbon feedstock and will need to resort to using high carbon steel. If designers want to take a global view, then a scrap steel content of 40% should be used (for all steel products) in the embodied carbon calculations[1]. Doing so would affect the embodied carbon ratings of different design options and may make meeting net zero carbon targets more difficult.

Aluminium
Market standard aluminium has around 35% recycled scrap content and has an embodied carbon rate of around 8300kgCO₂e/tonne. Virgin aluminium has 30% higher embodied emissions and should be avoided. It is possible to source aluminium and aluminium products that make use of >90% recycled content with embodied carbon rates in the region of 2000 kgCO₂e/Tonne. Designers and contractors should consider the feasibility of procuring specific aluminium products with high recycled fractions. The global supply of scrap aluminium (low carbon feedstock) is limited in much the same way as it is for scrap steel, albeit to a different extent, therefore the supply of low embodied carbon aluminium is similarly limited.

Another strategy for limiting embodied carbon of aluminium is to source products from factories powered by renewable or low carbon electricity (of which there are several in Europe). Finally, powder coated finishes are likely to incur lower embodied emissions than anodizing.