Resilience + Durability

A building’s longevity is an important element of sustainable design. Within LCA, this is due to the recurring embodied impacts associated with maintenance, the replacement of building components and needed renovations. However, it is also fundamental to the broader goal of making sure a building’s service life is not prematurely cut short, triggering the environmental costs associated with a new building. Whether a building is made from concrete, steel or wood, durability can be achieved through proper design, specification, detailing, quality control and maintenance.

How a building will perform during a catastrophic event is another consideration. With a wood building, for example, it’s useful to know that building codes require all buildings to be designed to the same level of fire and safety performance, and to understand wood’s capabilities in a seismic or high-wind event.³⁸

It’s also important to consider a building’s environmental impacts against its realistic life span. For example, it has been suggested that concrete should be used for buildings because it can last 100 years. However, research indicates that there is actually no significant relationship between the material used for a building’s structural system and its service life.³⁹ Rather, a study of buildings demolished in the Minneapolis/St. Paul area found that most were demolished because of changing land values, changing tastes and needs, and lack of maintenance of non-structural components.⁴⁰

Among the findings:

• Only eight buildings (3.5 percent) were demolished because of structural failure.
• Wood buildings in the study were typically the oldest; the majority were older than 75 years.
• More than half of the concrete buildings fell into the 26- to 50-year category, with only a third lasting longer.
• Approximately 80 percent of the steel buildings demolished were less than 50 years old, and half were less than 25.

Overall, the fact that wood buildings had the longest life spans shows that wood structural systems are fully capable of meeting a building’s longevity expectations; however, considering the embodied energy in demolished buildings and the implications of material disposal, the fact that wood is adaptable either through renovation or deconstruction and reuse is a significant advantage.

End of Life

Although demolition signifies the end of a building’s life cycle, it is not the end for building materials, which still face disposal, recycling or reuse. For obvious reasons, recycling and reuse are encouraged and rewarded by green building rating systems. However, the challenge in any recycling or reuse program is effective material recovery.

Although steel is said to be the world’s most recycled material, a recent report by Dovetail Partners challenges long-standing beliefs about steel recycling.⁴¹ For example, rather than the 88 percent recovery rate reported by the Steel Recycling Institute, researchers determined that the actual rate was less than 60 percent.⁴² The report concludes that “commonly used definitions of recycling serve to obscure actual recovery and recycling performance, that there are considerable losses of material with each use cycle, and that the often cited claim that steel is continuously recyclable without loss of quality is not true. [They] also found a much greater potential for steel recovery and recycling than is currently being realized.”

The results of this report are important, not to diminish the value of steel recycling, but to ensure that the need for improvement is recognized and the necessary investments are made to achieve greater recycling performance. For concrete, recycling has become an accepted way to dispose of demolition waste that was once routinely shipped to landfills. According to the Cement Sustainability Initiative (CSI), most recycled concrete is used as aggregate in road sub-base; however, the industry also promotes its use in structural concrete.

Although current statistics are difficult to come by (the collection of better waste data is a CSI recommendation), an estimated 50 to 60 percent of waste concrete in the United States is recycled. More than 2 billion tons of aggregate are consumed each year, and about 5 percent of that is recycled material.

For wood, the potential for improvement is greater. While reclaimed or salvaged lumber is increasingly finding new life as beams, exposed trusses, millwork, flooring and furniture, another report from Dovetail Partners estimates that 32 percent (11.1 million tons) of wood in the U.S. municipal waste stream and 48 percent (17.3 million tons) of wood in the construction and demolition stream are not yet being recovered.

To help resolve this, the American and Canadian Wood Councils recently partnered with the Building Materials Reuse Association to develop a North American directory outlining reuse and recycling options for wood and wood products (www.reusewood.org). The directory lists companies within a searchable geographic area that have agreed to provide reuse and recycling options for wood and wood-based products. Unlike concrete and steel, the recovery of wood has an added incentive. The reclaimed wood continues to store carbon while its use in place of new materials offsets any associated greenhouse gas emissions.