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Materials In Action

Wood, concrete, and steel have an environmental impact on building construction, operation and end of life

November 2013
Sponsored by reThink Wood

Continuing Education

Use the following learning objectives to focus your study while reading this month’s Continuing Education article.

Learning Objectives - After reading this article, you will be able to:

  1. Evaluate the durability and versatility of wood, concrete, and steel.
  2. Explain how current building codes permit the extended use of wood.
  3. Articulate the importance of embodied and operating energy.
  4. Discuss a building material's end-of-life issues.

Credits: 1.00 HSW


This course was approved by the GBCI for 1 GBCI CE hour(s) for LEED Credential Maintenance.

This test is no longer available for credit

When an architect specifies a building material, that choice casts a long shadow. While most of the environmental effects from materials occur during the extraction and production phases, the building material influences a structure’s environmental footprint well after, throughout the operations phase and beyond. What are the life cycle costs of the material? How durable is it? Is the material thermally efficient? Is it susceptible to moisture damage? Can it withstand seismic activity? What are the code considerations? Can it be recycled or reused, and at what cost to the environment? These are the kinds of questions that should be considered in the earliest project phases. The answers will determine, in part, a structure’s sustainability quotient. This article will address, through research and facts, the differences between wood, concrete, and steel in terms of basic material properties as well as their performance during the building operations phase. Topics will also include end-of-life issues, including the impacts of recycling and re-use, and code changes that have allowed the increasing use of wood in construction.

Design Considerations

Prior to specifying a material, certain issues should be thoroughly investigated.

Durability

Good design and quality construction are important factors in a building’s longevity, as is maintenance. “Any building of wood, concrete or steel could last an indefinite period of time, provided there is proper maintenance," says Scott Lockyear, Senior National Director for U.S. WoodWorks, an initiative of the Wood Products Council established to provide free technical support and education related to non-residential and multi-family wood buildings. “The critical thing is moisture control. Without it, concrete will spall, wood will decay, and steel will rust."

Exterior of Arena Stage, Mead Center for American Theater, Washington, D.C. Hybrid wood, concrete, and steel structures are often good solutions in sustainable building.

Photo by Nic Lehoux courtesy of Bing Thom Architects

Wood buildings have lasted for centuries.

Building materials tend to deteriorate and fail via well-known mechanisms. Fungi are the major cause of wood deterioration when wood is exposed to constant wetting without preservative treatment or the ability to dry. However, wood is relatively resistant to high humidity and many of the conditions and chemicals that adversely affect steel and concrete, such as corrosive salts, dilute acids and sea air. Provided its surface is protected from rust, steel can maintain its strength indefinitely. For construction steels, corrosion is the most common and expensive form of material degradation.

The most effective and common procedure for preventing or slowing corrosion is to eliminate contact with water, either by coatings or by protection within a building envelope. Steel studs and many other components are protected from water electrochemically by galvanizing, which does not eliminate contact with water. Although concrete itself does not corrode or decay, it almost inevitably cracks, and concrete cannot be used structurally without steel reinforcement. Cracking of concrete exposes concealed steel reinforcement to more moisture and corrosive chemicals which, in turn, further erodes the steel components and leads to further cracking and spalling of concrete.

Steps to Decades of Reliable Service

To enable wood to have a long service life, the following four factors are critical:

Moisture control
Architects should fully understand moisture loading, including the source of water, how the water is transported, and how to control and remove it. Wood construction maintained at a moisture content of 19 percent or less will not decay. In fact, decay doesn't generally occur until the moisture content reaches 26 percent or more. Protected from water or vapor condensation, exposed to normal atmospheric conditions, interior wood has a moisture content that rarely exceeds 14 percent.

Termite control
As termites thrive in wet environments, controlling moisture goes a long way toward controlling termites. Soil and foundation barriers and bait systems can also help prevent infestation by insects.

Use of durable materials
Wood that comes into contact with the ground or certain climates may need greater protection; naturally durable wood species, such as yellow-cedar or Douglas-fir, or preservative-treated wood may be necessary.

Quality assurance
Where moisture and/or insects are an issue, quality control is critical in constructing building assemblies to resist negative effects, as is proper maintenance to keep the structure dry.

 

Originally published in the May 2011 issue of Architectural Record; updated in November 2013
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