Energy Efficient Wood Buildings
HEAVY TIMBER/HIGH PERFORMANCE
Photo courtesy of John Stamets
The Bullitt Center Seattle, WA Architect: The Miller Hull Partnership
Described as the greenest commercial building in the world, the Bullitt Center has surpassed its net-zero energy goals, sending a surplus back to the local power grid in its first year of operation. The six-story, 52,000-square-foot structure includes four stories of heavy timber construction over a two-story concrete podium and was designed to meet stringent requirements of the Living Building Challenge (LBC). While M/E/P engineer, PAS, predicted 16 kBtu per square foot—half the energy-use intensity of Seattle’s next best-performing office building—the building has already achieved a significantly lower 10 kBtu per square foot.
When Bullitt was conceived, the design team expected to use a reinforced concrete frame because they thought they needed it for thermal mass, but when they considered the embodied energy and carbon footprint of the concrete, timber turned out to be a better environmental solution. To let in as much natural light as possible, the design required high ceilings and tall windows. The architect chose 2”-by-6” lumber set on edge and nailed in place to create relatively shallow solid wood floor panels, which helped to increase daylight penetration.
Architect Brian Court attributed the building’s over-achievement to its occupants, whose plug loads have been considerably less than expected.
Conclusion
While wood has low thermal conductivity, other factors—such as the use of high-efficiency windows and doors, high levels of insulation, and air sealing—have a greater influence on a building envelope’s energy efficiency than choice of structural material. In specifying wood, the more relevant point for many designers is that wood building systems lend themselves to structures that are energy efficient, with less impact on the environment in terms of embodied energy, air and water pollution, and carbon footprint than other major building materials.6
Additional Resources
This continuing education course draws from the FPInnovations Guide for Designing Energy-Efficient Building Enclosures for Wood-Frame Multi-Unit Residential Buildings in Marine to Cold Climates in North America. These areas tend to have the greatest need for guidance in order to meet increasingly stringent energy code requirements. While much of the information is relevant in other climate zones, FPInnovations is developing similar guides for the hot-dry/hot-humid and arctic climates.
The following resources are also available to assist designers with the energy-efficient design of wood buildings:
- Design for Code Acceptance 7: Meeting Residential Energy Requirements with Wood-Frame Construction, 2014, American Wood Council
- Thermal Performance of Light-Frame Assemblies, Canadian Wood Council
- Energy and the Environment in Residential Construction, Canadian Wood Council
- U.S. CLT Handbook, FPInnovations, 2013
Additional information on the design of mid-rise wood buildings is available from the U.S. WoodWorks program (www.woodworks.org) and American Wood Council (www.awc.org).
Endnotes
- Guide for Designing Energy-Efficient Building Enclosures for Wood-Frame Multi-Unit Residential Buildings in Marine to Cold Climates in North America, 2013, FPInnovations
- Need for an embodied energy measurement protocol for buildings: A review paper, Manish K. Dixit, Jose L. Fernández-Solís, Sarel Lavy, Charles H. Culp College of Architecture, Texas A&M University
- Ibid, Endnote 1
- USDA Forest Products Lab Wood Handbook, Chapter 4
- Research Report 0903, Straube. J., J. Smegal, 2009, www.buildingscience.com
- Werner, F. and Richter, K. 2007. Wooden building products in comparative LCA: A literature review. International Journal of Life Cycle Assessment; Life Cycle Environmental Performance of Renewable Building Materials in the Context of Residential Construction – Phase I, 2005 and Phase II, 2010, Consortium for Research on Renewable Industrial Materials
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