Embodied Carbon Considered

Posted Jan 19th, 2023

Embodied carbon is a concept that has emerged over the past couple of decades.  “Embodied carbon is, to some extent, an odd beast…” (1, p.xi)  When people think of buildings relative to energy consumption and CO2 emissions, they usually think of the energy used for heating and cooling, but there is another dimension.  The basic creation and refurbishment of the fabric of buildings has implications too.  Accordingly, the concept of embodied carbon has emerged, which refers to the emissions that are released in development and construction.  Many aspects of this are hidden – because the supply chains relating to building materials can be long and complex, and that complexity relates to some commonplace, but energy-intensive materials, such as steel, concrete and aluminum.  One way of conceptualising this, is to think of the emissions as somehow being ‘attached’ to the fabric of the building itself.  It is believed that embodied carbon represents about ten percent of all emissions associated with buildings worldwide(2).

The ongoing energy and emissions implications of any building can, and likely will, be modified over time, as refurbishment and changes of use occur, and new technologies come to replace older equipment, however most of the embodied carbon implications of a building almost always result from initial construction.  The recent nature of the subject, and the complex nature of supply chains mean that this remains an evolving field. 

The American Institute of Architects offers ten ways to reduce embodied carbon in buildings(3).  Some of their research has suggested that the embodied carbon in a building can represent as much as ten years of operating emissions. 

1. The first suggestion is obvious (as are many of them)– reuse buildings rather than demolishing them and building new ones. 

2. The biggest factor in the embedded carbon of many buildings is concrete.  Indeed, it has been estimated that concrete production alone is responsible for eight percent of total global CO2 emissions, and have doubled over the past two decades(4).  The AIA suggests considering the use of lower carbon concrete, but notes that how to do that varies from place to place.

3. Using carbon-intensive materials sparingly is suggested, together with (4.) considering the use of lower carbon-intensive alternatives.  Examples would be the use of wood rather than steel, concrete or vinyl.   

5.  Carbon sequestering materials can be used – these are typically natural products that retain carbon, such as wood, hemp or bamboo.

6.  Reuse materials that have been salvaged, or (7.) are made of recycled materials, such as recycled steel. 

8.  The biggest single building element in the embodied carbon calculation is usually the structure.  That means attempting to achieve maximum efficiency in the use of materials in the building structure.

9.  The AIA suggests using fewer finish materials, perhaps by using basic structural materials as finish.  This might be debated, especially if the implication is to use more of those high-embedded carbon structural materials, and often, there are cost implications in making structural elements suitable for finishes.   

10..  Minimize waste – a rather obvious point, but it does mean, in particular relative to wood&mdashframed buildings to make sure dimensions correspond to the extent possible with standard product sizes.

Exploring embodied carbon matters lead to numerous questions.  Operational carbon emissions can be calculated from a building’s electrical and gas consumption – which are itemized in bills.  It is not so easy for determinations of embodied factors.  In the calculations, it is desirable to include all emissions that are associated with construction, including obviously installation and manufacturing, but also back through the supply chain to include transportation and even extraction of the fundamental materials, such as the mining of iron ore, or extracting aggregates, and forward to demolition and disposal of the materials.  Moreover, even in identical products or materials, the amount of embodied carbon can vary substantially – whether a beam was made from recycled steel, and how far and by what means was it transported on its journey to the site. 

All of this means that, while useful data bases are available, estimates of embodied carbon will always have a substantial range of uncertainty around the actual values.  Nevertheless, it is possible for the designer, using his/her experience and insights, to reduce the amount of embodied carbon in a construction project – primarily by focussing on the structural components, following the advice of the American Institute of Architects (AIA). 

Matters of time, uncertainty, and building and building-element life expectancies, were dealt with in various chapters in the book ‘Embodied Carbon in Buildings’ edited by Pomponi, DeWolf and Moncaster (1).  The various contributors identified elements of uncertainty in assessing the embodied carbon in buildings.  These include:

Uncertainty about the current embodied carbon of construction materials, components and, ultimately, whole buildings; Uncertainty about the embodied carbon of construction materials and components that may be available in the future, as a result of market changes and technological innovation; Uncertainty about future events in the service life of built assets, including length of component life, the nature and timing of component replacement or substitution, intensity of use, changes of use, and end of life events; Uncertainty about system boundaries and methods of measurement;  Uncertainties with respect to specific locations and orientations of buildings.

Analysis of embodied carbon is in important part of Life-Cycle Assessment (LCA) which is the method of understanding the overall environmental impacts of products and services.  However, there is also Life Cycle Costing (LCC) a process that explores the economic aspects of various alternatives.  In the building world, a complete assessment has to consider not just initial investments of money and resources, but also longer-term implications of future maintenance, replacements waste treatment, all with respect to the life-expectancies of the building system elements.  The integration of these is difficult, but can be illuminating.  Cases and concepts with regard to the relationships of these is explored in a book based on European research:  Sustainability within the Construction Sector:  CILECCTA – Life Cycle Costing and Assessment(5).  Exhibit 1.1 in this document shows three hypothetical project alternatives as fuzzy blobs of uncertainty around assessments of LCA (measured in terms of CO2 emissions) and LCC (measured in terms of money).  This recognises the uncertainty inherent in any of these attempts to bring long-term processes to an initial starting point.  Of course, a large proportion of embodied carbon is emitted during the construction phases, but buildings often have long, complex and uncertain lives that must be considered.

Two factors clutter an analysis.  One is the uncertainty that infests almost every aspect of the embodied carbon question.  Many studies approach at least part of their work deterministically – that things can be definitively known.  The other is the need to balance different things – not just embodied and operational carbon emissions, but with needs to protect forests, farmlands and endangered species, and the social, cultural and economic needs of present and future generations.  There is also the matter of how to deal with the ongoing change in technologies – in a hundred years, will we still be getting around in rubber-tired vehicles running on asphalt surfaces, or even commuting to places of work?  Amazing strides are being made in the matter of fusion-generated energy – it does not have to happen, but even that possibility changes the ways we might invest in the present.  In the 1970s, after the energy crisis, a local government was proposing to destroy a historic neighbourhood on the basis that with rising oil costs, the area was doomed – no-one would be able to afford to live in the houses.  Fifty years later the neighbourhood is thriving – the houses now have more efficient heating systems and have upgraded insulation and windows, commuting to work is less pronounced, and increased affluence means that the cost of heating has become a smaller proportion of incomes.  Some of the larger houses have been divided into delightful apartments.  If that local government had simply assumed that the world would continue unchanged, it would have destroyed an area that they now point to with pride. 

This haziness about the future does tend to discount future implications of any building, enhancing the relative value to be derived from consideration of embodied carbon (as well as other economic, environmental and social/cultural concerns). 

Two possibilities seem to exist, one being a full inventory of initial and ongoing embedded carbon implications, as adjusted for uncertainty, or, perhaps more practically, just following the American Institute of Architects basic ten guidelines. 

Sources and for more reading…

(1)    Pomponi, Francesco; DeWolf, Catherine; and Moncaster, Alice (eds.) (2008) Embodied Carbon in Buildings:  Measurement, Management and Mitigation, Springer. 

(2)    Strain, Larry 10 steps to reducing embodied carbon,  American Institute of Architects, https://www.aia.org/articles/70446-ten-steps-to-reducing-embodied-carbon  Accessed 7 Dec, 2022

(3)    Canada Green Building Council (2021)  Embodied Carbon: A Primer for Buildings in Canada

https://www.cagbc.org/wp-content/uploads/2022/03/Embodied-carbon-white-paper-March-2022.pdf    Accessed, 6 Dec, 2022

(4)   Vaughn, Adam (2022)  Firms pledge to clean up construction with green net-zero concrete, New Scientist, 5 July 2022.  https://www.newscientist.com/article/2326934-firms-pledge-to-clean-up-construction-with-green-net-zero-concrete/

(5)   Sustainability within the Construction Sector: CILECCTA – Life Cycle Costing and Assessment (2013), SINTEF Academic Press: Oslo.

This piece was prepared by Ian Ellingham, MBA, PhD, PLE, FRAIC, who is an architect and land economist.  He has worked on research funded by various government bodies in Canada and Europe, and by the private sector, and was a co-author of one of the chapters of Embodied Carbon in Buildings:  Measurement, Management and Mitigation