From an environmental perspective, it is widely known that buildings matter. Buildings consume nearly half the energy produced in the United States, use three-quarters of the electricity and account for nearly half of all carbon dioxide (CO₂) emissions.¹ The magnitude of their effects is the driving force behind many initiatives to improve tomorrow’s structures—from energy regulations and government procurement policies, to green building rating systems and programs such as the Architecture 2030 Challenge. The focus on energy efficiency, in particular, has led to widespread improvements, so much so that many designers are now giving greater attention to the impacts of structural building materials.

With an abundance of information and competing environmental claims, determining a material’s true impacts can be a challenge. Does wood reduce a building’s carbon footprint in a meaningful way? Is it better to use recycled steel or wood from a sustainably managed forest? To what extent do structural materials impact operational performance? Does resilience depend on the material or on proper design and maintenance?

This course seeks to address these and other questions. Examining materials throughout their life cycles, it focuses on international research supporting the use of wood for its carbon and other benefits while considering some of the advantages of concrete and steel. It also touches on the efforts by all three industries to lessen their environmental impacts. The reality is that no one material is the best choice for every application. There are trade-offs associated with each, and each has benefits that could outweigh the others based on the objectives of a project.

Clay Creative | Architect: Mackenzie | Photo: Christian Columbres

Importance of a Life-Cycle View

Understanding a material’s impact at every stage of its life is essential for designers looking to compare alternate designs or simply make informed choices about the products they use. Life-cycle assessment (LCA) is an internationally recognized method for measuring the environmental impacts of materials, assemblies or whole buildings, from extraction or harvest of raw materials through manufacturing, transportation, installation, use, maintenance, and disposal or recycling.

LCA is sometimes described as mysterious and complicated. Yet what is involved is simply a thorough accounting of resource consumption, including energy, emissions, and wastes associated with production and use of a product. For a “product” as complex as a building, this means tracking and tallying inputs and outputs for all assemblies and subassemblies—every framing member, panel, fastener, finish material, coating and so on. To ensure that results and data developed by different LCA practitioners and in different countries are consistent, LCA practitioners must adhere to a set of international guidelines set forth by the International Organization for Standardization (ISO).

The use of LCA in North America is increasing due in part to the availability of easy-to-use and affordable tools (see sidebar, "Calculating the Impacts of Building Designs"). LCA is also included in all of the major green building rating systems, providing an alternative to the “prescriptive approach” to material selection. This approach assumes that certain prescribed practices, such as specifying products with recycled content, are better for the environment regardless of the product’s manufacturing process or disposal. It was a cornerstone of early green building efforts, when there was relatively little information available on the impacts of individual products at different life-cycle stages.

LCA studies consistently demonstrate wood’s environmental advantages. For example, one literature review examined all of the available research from North America, Europe and Australia pertaining to the life-cycle assessment of wood products.² It applied LCA criteria in accordance with ISO 14040-42 and concluded, among other things, that:

• Fossil fuel consumption, the potential contributions to the greenhouse effect and the quantities of solid waste tend to be minor for wood products compared with competing products.
• Wood products that have been installed and are used in an appropriate way tend to have a favorable environmental profile compared with functionally equivalent products made from other materials.

The table below illustrates the results of an LCA comparing a simple commercial structure designed in wood, steel and concrete. Designed for the Atlanta geographical area, the building footprint was 20,000 square feet (100 feet by 200 feet). The structure is two stories in height and 20 feet tall, with 40,000 square feet of total floor area. To simplify analysis, the theoretical building was analyzed without windows, doors or internal partitions. All three configurations were assumed to have a concrete foundation and slab.

The analysis involved systematic assessment, using life-cycle methodology, of all building assemblies beginning with raw material extraction through primary and secondary manufacturing, transport at all stages of the production chain and to the job site, and building construction. As shown in the table, impacts for the wood design are lower than either the steel or concrete design across all indicators.

Source: Athena EcoCalculator