Discussions of “sustainability” in architecture and construction often focus on materials and energy use. These performance measures relate to the environmental costs of constructing and maintaining a building. Unfortunately, the performance of the structural system, the skeleton of a building, is often not considered as a critical item in the overall sustainability strategy. In November 2014, Megan Stringer, Project Engineer at Holmes Culley, gave a persuasive presentation about the critical role structures can play in sustainability.
Ms. Stringer has been leading research on the topic of Sustainable Structures in her role as chair of Sustainable Design Committee for the Structural Engineers Association of Northern California. She argues that building a highly resilient structure–one that can withstand unusually strong seismic or other natural events–can be a critical decision leading toward sustainability. Currently, most buildings, including those recognized for their sustainable measures, are designed to Code minimum standards. The Code focuses on the importance of preserving life through collapse prevention but a building may be completely unusable after a major event. Following the Christchurch, New Zealand earthquake of 2011 about 70% of damaged buildings were demolished. The benefit of strengthening beyond the requirements of code can be a longer lasting building, which proves to be more sustainable in the long run.
It’s worth noting two concerns Ms. Stringer acknowledged with regard to building stronger structural systems. First is added cost. The typical cost of the structural component of a building is 10% to 20% of the total construction budget. Increasing the resiliency of the structural system does require more materials and labor. Depending on the level of upgrade for the structural system, the additional cost can be in the range of a 10% increase to the structure’s budget. This translates to only a 1% increase in overall construction budget. The payback of the additional measures can be enormous when viewed against costs related to downtime after an earthquake, loss of property, cost to repair damage or cost to replace a building. These considerations should be evaluated when setting the project objectives.
Another trade off of creating a stronger structural system is that it uses more materials. This seems to counter one of sustainability’s prime tenets – do more with less. The general idea is that less material has less impact on the environment. However the lightest structural design will probably not be the most resilient approach and may not support other requirements of the project, such as acoustic dampening. To get perspective on the issue Ms. Stringer and her team turned to the use of a Life Cycle Analysis (LCA) tool. The LCA considers all the parameters of a material including manufacturing, transportation and end of life help understand the carbon footprint and global warming impact of a material over its entire life. Their study examined a theoretical building designed to meet the same structural performance. By varying the structural materials used (typically being wood, steel or concrete) they were able to show a correlation between heavier materials and the global warming impact. Concrete was the highest impact while wood was the lowest. The cost of these systems often vary with location and availability but with new technologies we will see the rise of wood being used more in large building structural systems.
Long lasting buildings are becoming more of a critical economic factor for property owners because of rising construction and energy costs. Often a building will outlast its original intended use leading to another reason to consider resiliency. Paula Melton reports in the Nov. 2014 issue of Environmental Building News about the benefits of renovating buildings. Several of the studies Ms. Melton discusses show that as a result of the embodied energy in existing structures they are typically a better sustainable option than new construction. A renovated building benefits from the embodied energy in the existing materials (predominantly the structure and exterior walls) and reduces the carbon footprint of construction. One study quoted looked at the operational energy savings of renovated buildings compared to new construction. The analysis showed the energy savings from upgrades in renovations typically had long term savings while new construction could take up to 80 years of operational energy savings to offset the carbon footprint of construction.
Thoughtful design considers all aspects of sustainability in the creation of adaptable, durable, and resilient buildings. WDA thanks Ms. Stringer for her thoughtful research, which reminded us that renewal–in the form of reusing and reinforcing an existing building or designing a new, resilient building that can be adapted in years to come–is a key component to sustainability.