Materials In Action

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

In some instances, a material with no recycled content can actually be a more sustainable choice than a recycled material. Steel, for example, typically has at least 25 percent recycled content, while most structural wood products have none. But to achieve a higher recycled content percentage, manufacturers change the content or processing of a product in a way that has other environmental implications. Life cycle assessment illustrates these impacts. The accompanying bar chart uses LCA to compare the environmental profile of two standard structural post-and-beam systems (one with wood and one with steel), and a third option using a theoretical steel with 100 percent recycled content. The wood system is glulam beams on wood columns with no recycled content. The steel system is standard wide flange beam on hollow structural section columns, recycled content is 25 percent, typical for the industry. The wood performance is set as the benchmark at 100 percent, and the other sets of bars are shown by percentage better or worse than the wood. Figures were calculated using The Athena Impact Estimator for Buildings.

An alternate to recycling is designing for deconstruction, which requires less use of resources—in other words, design to facilitate salvaging components during demolition for reuse in their original high-value format. The U.S. Green Building Council's Leadership in Energy and Environmental Design (LEED®) rating system encourages the use of both recycled and salvaged materials.

The Recycled Content credit (MRc4) rewards materials with recycled content such that the sum of post-consumer recycled content plus 1/2 of the pre-consumer content constitutes at least 10 percent (1 point) or 20 percent (2 points), based on cost, of the total value of the materials in the project.

The Materials Reuse credit (MRc3) rewards projects that “use salvaged, refurbished, or reused materials, the sum of which constitutes at least 5 percent (1 point) or 10 percent (2 points), based on cost, of the total value of materials on the project."

Another rating system that’s gaining traction is the Living Building Challenge (LBC), a program of the Cascadia Region Green Building Council, which encourages increasing improvements, rather than reducing impacts. In contrast with LEED®, LBC projects are not certified until they have proven their intended design and requirements. Among the projects to achieve certification so far: the Living Learning Center at Tyson Research Institute, near St. Louis, and the Omega Institute in Rhinebeck, New York, both of which make high use of salvaged materials, particularly wood.

At this time, using salvaged materials is not without its obstacles. The salvaged wood market is established in some areas, with large timbers and old growth lumber especially sought after. Salvaged wood requires very little additional energy to process, and is generally confined to transportation. As with wood, steel salvage yards exist in some regions. Yet one of the greatest disincentives to using salvaged material of any type is that it is not always on hand in the right dimension, amount, or timeframe—a situation that could be remedied by basing a design on the availability of the salvage.

Evolving Building Codes

Coupled with advances in wood science and building technology, increasing recognition of wood's structural and performance capabilities has expanded the options for wood use in construction. Earlier in this article, reference was made to the fact that CLT is scheduled to be included in the 2015 IBC. This particular code change is getting a lot of attention because of the groundbreaking nature of CLT; nine- and ten-story CLT buildings exist and exciting concepts have been developed for going higher still. However, the possibilities for wood use have actually been expanding since the IBC was introduced in 2000.

The University of Washington West Campus Student Housing project includes five buildings, each with five stories of wood-frame construction over two stories of concrete. This 2-story podium configuration, which is common in Seattle and will also be permitted under the 2015 IBC, allowed the project team to meet ambitious design goals within the University's tight budget.

Photo courtesy of W.G. Clark Construction and Mahlum Architects

The IBC consolidated three regional model building codes into one uniform code that has since been adopted by most jurisdictions. It created more opportunities for wood use by (among other things) recognizing additional fire protection techniques, and combining the maximum allowable heights and areas from the three legacy codes into one (thus increasing what's allowable in some jurisdictions).

In a Type III building, for example, it is possible to achieve an eight-level wood building that's approximately 85 feet high. Like all construction types, Type III has base limitations with regard to height, number of stories and square footage. However, the IBC allows increases to these tabular amounts per other code sections. For example, when a building has an NFPA 13-compliant automatic sprinkler system, the floor area can be increased by 300 percent for a one-story building and 200 percent for a multi-story building. In addition to the area increase, IBC Section 504.2 allows a 20-foot increase to the tabular building height and an additional story above the grade plane. The exception to this is Group I-2 occupancies, which include hospitals and nursing homes and are not allowed the extra story.

 

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Originally published in Architectural Record
Originally published in November 2013

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