Case Studies

Cole and Kernan studied the embodied energy of a typical Canadian office building constructed from three different structural systems: wood, steel, and concrete. The case study building was a 4620m2, three-storey office building located in Canada. The following figures were produced from the findings.

In Figure 1, the distribution of the total initial embodied energy for the building averaged over steel, wood, and concrete construction. It was found that the building services, envelope, and structure each account for roughly one quarter of the initial embodied energy in the average Canadian office building.

Figure 1: Total Initial Embodied Energy of a Typical Canadian Office Building Averaged Over Steel, Wood, and Concrete Construction (Cole & Kernan, 1996).

In Figure 2, a comparison was made between the initial embodied energy and the recurring embodied energy for the case study building over 100 years. The results for the wood building type were plotted; however, the results for the steel and concrete buildings would exhibit a similar overall trend.

The results show that over any significant life-cycle, the recurring embodied energy associated with the building outweighs the initial embodied energy. Also, there is no recurring embodied energy associated with the structural system. Therefore, after the structure of the building is erected at time zero, it’s assumed no major maintenance or repair has to be done to the structural system over the building’s life span. Thus, any differences in embodied energy between a wood, steel, or concrete structural system occur initially. The initial embodied energy of the structural system varies depending on whether wood, steel, or concrete are used, plus there is no recurring embodied energy associated with the structural system.

Results of this study show that beyond 50+ years the recurring embodied energy associated with the finishes, envelope, and services completely dominate the embodied energy of the overall building. Therefore, the focus should be on reducing the recurring embodied energy of these three components as a first step in reducing the embodied energy of the overall building.

Figure 2: Initial Embodied Energy vs. Recurring Embodied Energy of a Typical Canadian Office Building Constructed from Wood over a 100-Year Lifespan (Cole & Kernan, 1996).

"The results show that over any significant life-cycle, the recurring embodied energy associated with the building outweighs the initial embodied energy."

Figure 3 compares the total initial embodied energy of a typical Canadian office building vs. material type. Cole and Kernan found there to be a difference in the initial embodied energy of the three structural systems: wood, steel, and concrete.

The initial embodied energy for the wood structural system was found to be about 55% of the initial embodied energy of steel structural system and about 72% of the initial embodied energy of the concrete structural system. Cole and Kernan found very little difference in the initial embodied energy for the other parameters: site work, construction, finishes, envelope, and services depending on which structural system was chosen. Also, the initial embodied energy that’s associated with the choice in structural system is a fraction of the total initial embodied energy for the entire building. It was found that the combined effect of the non-structural components such as: building finishes, envelope, services, etc. outweigh the initial embodied energy of the structural system. Thus, although there is a difference in the initial embodied energy of the structural system depending on which material is chosen, these discrepancies are minor in the greater picture.

"Justification for using one structural system over another cannot be made based on initial embodied energy figures alone, rather it must be based on a holistic life-cycle assessment of the greater goals."

Things such as the building envelope, services, finishes, etc., which are common across all structural systems, often contain greater proportions of materials with very high embodied energies like copper and plastic, which tend to dominate from the standpoint of embodied energy. Justification for using one structural system over another cannot be made based on initial embodied energy figures alone, rather it must be based on a holistic life-cycle assessment of the greater goals. Further, examining the typical operational energy for a building, the embodied energy in a typical building is less than 15% of the overall energy consumption in a building. Claims of using one material over another based on initial embodied energy arguments should be made in consideration of the fact that embodied energy is a relatively small component of the overall energy use in a typical building.

Figure 3: Total Initial Embodied Energy of a Typical Canadian Office Building vs. Material Type (Cole & Kernan, 1996).