Where does embodied carbon analysis stop?

[edit] Introduction

It’s easy to get caught up in the nitty-gritty details of analysing the embodied carbon of a building. We dive into calculating the weights of materials used, multiply these by an embodied carbon factor, and determine the tonnes of carbon dioxide equivalent that are emitted in producing the materials for a project.

However, it is important to extend our view beyond the product manufacture cycle. Below, KLH discuss three key areas that are often considered too late, if at all, in carbon analysis.

[edit] Transportation

Many Environmental Product Declarations and product databases list the emissions associated with the ‘Product Manufacture and Supply’. This is commonly known as ‘cradle-to-gate’, and relates to the raw materials, transportation and processing up to the point where the product is ready for distribution.

This does not include transportation to the project site. The benefits of a low-carbon material might be outweighed by the emissions associated with transportation if you have to bring it from the far reaches of Scotland (depending on how you transport it, of course).

DEFRA publish carbon emissions rates of various modes of transport on an annual basis. Using these rates, together with the travel distance, it is possible to estimate the carbon impact of distribution. Although it is worth noting that the average values provided by DEFRA do not accurately represent carbon emissions of bulk material transport, where weight rather than volume is the limiting factor on the amount of material transported.

There is an opportunity to review procurement strategies to incorporate sustainable transportation of materials, such as by rail or water, or choose to source more locally. Not only does this reduce the embodied carbon associated with transportation, there are also wider social benefits to removing HGVs from roads, such as reducing congestion, accidents and air pollution.

[edit] Material replacement cycles

A second area that is often overlooked in embodied carbon analyses is the impact of a material’s service life in comparison to the expected life of a building. The number of times an element will need to be replaced to ensure continued serviceability of the building, should be considered when comparing different options for elements.

Another example is when investigating different types of pavement construction, such as asphalt versus stone or concrete block paving. Wherever a number of products could fulfil a specific function, it is vital to consider replacement cycles if we are to deliver low carbon buildings and infrastructure.

[edit] Embodied versus operational carbon

A third area to consider is the relationship between embodied carbon and its influence on operational carbon emissions. The drive to reduce operational carbon can result in an increase in the embodied carbon. One situation where this is most evident is in the insulation of the building envelope.

Thicker and higher performing insulation is often required to achieve stringent targets for reducing operational energy over the building’s life span. The embodied carbon of a selected insulation needs to be evaluated alongside the required thickness to achieve specific thermal performance, and the embodied carbon implication of the overall wall build-up.

In the majority of cases, the additional embodied carbon of the increased construction thicknesses will be offset by the improved operational performance, provided that design details and construction delivery are adequately attended to.

The three considerations described above give a taster as to why it is important to understand the context, wider influences and trade-offs that impact on a project’s embodied carbon before beginning with the analysis.

So before you calculate the carbon dioxide emissions to the fourth decimal place, make sure that what you are calculating gives due consideration to the procurement, construction and life-cycle operation of the building or infrastructure, and acknowledge that the complexity of reality can never really be fully represented in the simple calculation presented.

--KLH Sustainability

[edit] Related articles on Designing Buildings Wiki

• Carbon footprint.
• Embodied energy in construction.
• Fabric first.
• Life cycle assessment.
• PAS 2080 Carbon management in Infrastructure.
• Performance gap.
• Sustainability in building design and construction.
• Utilising life cycle costing and life cycle assessment.