Q4: How much of total embodied impact comes from structure?

A rule of thumb often stated within the building design community is that the structure accounts for approximately 50% of a building's life cycle embodied energy.  

Author: Terry McDonnell; Contributors: Frances Yang, Kate Simonen, Rebecca Jones

This article examines three main scenarios for the amount of embodied energy due to structure compared with the entire building;

1. Structural Embodied Energy During Construction
2. Structural Embodied Energy Over Building’s Single Lifespan
3. Structural Embodied Energy Over Building’s Rebuilt or Repaired Lifespan

Structural Embodied Energy @ Initial Construction

There are numerous studies of structural embodied energy during the initial construction phase.  The following is a brief summary of those studies:

• In the embodied energy study by Kofoworola and Gheewala shows that the concrete and steel components of a 38 story reinforced concrete office tower in Thailand can be as high as 71% of embodied energy of a building through construction. (Kofoworola 2007)
• In the embodied energy study by Treloar et al shows that the concrete and steel components of a 15 story steel office tower in Australia can be as high as 90% of embodied energy of a building through construction. (Treloar 2001)
• The international building consulting firm Arup studied multiple pieces of literature and their own building designs in order to gather a data set of embodied energy that was bounded by “cradle to site”.  Calculations included all impacts of the extraction of the raw material, factory production and delivery to site.  Their analysis shows two interesting points;

           1) That the type of structure is not changing the significance of structural contribution to
           embodied energy.  Figure 4.1 shows a 50%-60% contribution independent of building type
           (Arup 2010).
           2) That the structural system may vary the contribution of embodied energy much more.
           Figure 4.2 shows that the structural system selected produces a range between 30%-60% of
           structural embodied energy compared to the entire building (Arup 2010). 

Figure 4-1:  Prepared by Arup (Kaethner 2012) Shows embodied energy vs. type of building use.

Figure 4-2, Prepared by Arup (Kaethner 2012), shows embodied energy vs. type of structural system.

Structural Embodied Energy Over Building’s Single Lifespan

Going further, one can look at the percent of embodied energy (or sometimes embodied carbon) of the structural materials throughout the entire life span of a building, including all operational impacts.  In most cases this will reduce the structural related percent vs. the total, especially during very long life spans.  Most building designs are benchmarked for 40-50 year life spans, but the exact amount is often determined during conversations between the building Owner and design team.   The following are studies and analyses performed in order to determine this value:

• An oft-cited study by R. Cole and P. Kernan based on the Canadian construction industry estimates that a 50,000 sft, 3 story office building using steel, concrete, and timber structural systems still produces a 25% to 33% range of the building’s total embodied energy. (Cole 1996)
• The carbon consulting firm dcarbon8, in a more recent case study conducted in 2007, calculated the total cradle-to-grave embodied carbon emissions (which are indicative of embodied energy) attributable to a warehouse building’s structure to be 57% of the total. (Werner 2012)
•  A similar study performed by Fernandez, N. Perez goes in depth to analyze an actual 55,000 sft, 6 story office building located in Christchurch, New Zealand.  Using the actual concrete design, and alternates of steel and timber, the author concludes that the life cycle structural embodied energy accounts for 30% of the concrete and timber designs, and 44% within the steel design alternate. (Fernandez 2008)
• Taking an actual four story, 80,000 sft office building located in Chicago, IL, a group of building designers studied four different structural systems using two separate material quantity calculations within the ATHENA EcoCalculator for the purpose of determining the structural material embodied energy.  By adding in non-structural components and using TRACE 2000 energy model each design assuming a 50 year life span.  The total embodied energy of the structure for this low rise building was determined to be between 6%-10% of the total cradle to grave energy.  This is lower than expected but remains a significant amount. (Stek 2012)

Structural Embodied Energy Over Building’s Rebuilt or Repaired Lifespan

Common practice in conducting an environmental life-cycle assessment (LCA) on a building includes a consideration of the impacts stemming from first construction of a building through its life span.   But in special circumstances, such as buildings in earthquake prone locations, the repair of damage or demolition and re-construction (sometimes referred to as multiple lives) of a building may significantly affect the overall structural embodied energy.  A comprehensive LCA includes impacts related to demolition but rarely includes the potential additional environmental impacts that could stem from repairing or demolishing and rebuilding a building after a natural disaster included in an LCA, if ever at all.  Methods are being developed to include seismic performance in LCA analysis.

One such study by Degenkolb attempts to include the affect of seismic systems within active earthquake locations in order to achieve a more accurate sense of a building’s full life-cycle impacts.  In this paper, an LCA study using the EnvISA methodology is performed.  This analysis measures common structural unit costs rather than a straight LCA inventory.  Anticipated seismic losses are then paired with the cost LCA database which forms the basis of EnvISA.  Their conclusions show that a more robust structural system can provide approximately 18% - 25% depending on the structural system selected, and how well that system can limit damage to the non-structural building elements over a 50 year life span. (Comber 2012)

The difficulty in all of the seismic evaluating studies is that they are to date based upon proprietary software.  Without knowing more about the system, the data sets, assumptions, inventories, boundary conditions, and actual measuring algorithm are different.

This brief paper shows that the often quoted rule of thumb that the structural materials are 20% of the total embodied energy is in reality subject to a lot of fluctuation.    Most cases presented show values higher than 20%.  As modern energy codes continue to reduce the operational energy, the percent of total embodied energy due to the structure will only increase.  In addition, the high rise building type has a much greater percentage of structural embodied energy out of the total.  Studies show that in buildings over 200 feet high (often times much more) the embodied energy can be 4 times or more of the embodied energy percentage of a shorter sized building. (Kaethner 2012)

Therefore it is relevant and altogether prudent to continue measuring and trying to decrease the environmental impact of structural materials.

References

Arup (2010) “Embodied Carbon Study: Study of Commercial Office, Hospital and School buildings,” The Concrete Centre, United Kingdom

Cole R., Kernan P. (1996) “Life-Cycle Energy Use in Office Buildings”, Buildings and Environment, 31 (4): 307-317

Comber, Poland, & Sinclair (2012) “Environmental Impact Seismic Assessment: Application of Performance-Based Earthquake Engineering Methodologies to Optimize Environmental Performance”, Victoria University School of Architecture, Wellington, New Zealand

dcarbon8 (2010) “Footprint Measurement and Reduction Study for Development Securities”

Fernandez, N. Perez (2008) “The Influence of Construction Materials on Life-cycle Energy Use and Carbon Dioxide Emissions of Medium Size Commercial Buildings”, Victoria University School of Architecture, Wellington, New Zealand

Hsu, S. (2010) “Life Cycle Assessment of Materials and Construction in Commercial Structures: Variability and Limitations,” Massachusetts Institute of Technology, Cambridge, Massachusetts

Kaether, Burridge (2012) “Embodied CO2 of Structural Frames”, The Structural Engineer.

Kofoworola, Gheewala (July 2007), “Environmental life cycle assessment of a commercial office building in Thailand”

Stek, DeLong, McDonnell, Rodriguez (2012) “Life Cycle Assessment Using Athena® Impact Estimator on Buildings: A Case Study”, SEI Congress 2012.

TRELOAR, G. J., FAY, R., LLOZOR, B. & LOVE, P. E. D. (2001a). Building Materials Selection: Greenhouse Strategies for Built Facilities. Facilities, Vol. 19, No. 3/4, pp,139 – 149

Werner, Burns (2012) “Qualification and Optimization of Structural Embodied Energy and Carbon”, SEI Congress 2012.

Other papers to research

Seppo, J.; Horvath, A., and Guggemos, A. (2006)  “Life-Cycle Assessment of Office Buildings in Europe and the United States,” Journal of Infrastructure Systems, March 2006 Issue.

CTBUH Journal, Tall Buildings and Embodied Energy, 2009 Issue III

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