Materials In Action
Adding an automatic sprinkler system not only means that a five-story wood building is allowed, it means a maximum height of 85 feet instead of 65 feet. The question then becomes, how can the vertical envelope be maximized to take advantage of the extra height when a typical five-story building is only about 55 feet? The first step is to add another level. Under the 2009 IBC, a wood-frame mezzanine can be added on top of a multi-story wood building. The area of the mezzanine can’t be more than 1/3 of the floor below and isn’t defined as a 'floor' or 'story.' Starting with the base height and then adding a sprinkler system and now a mezzanine brings the building to six levels of wood-frame construction and about 65 feet in height.
A Type I podium increases the height of the building even further. The wood-frame and concrete portions of a podium building are designed as two separate structures with a 3-hour fire separation in between. A podium designed for retail is typically about 15 feet high. So, adding the sprinkler system, mezzanine and now a podium takes the building to seven above-ground levels and about 70 to 75 feet in height.
The final step, to achieve 85 feet, is to use a sloping site to advantage. The IBC recognizes that the world isn’t flat. It allows semi-basements or daylight basements providing they don’t extend from grade more than 12 feet at any one point and don’t extend more than 6 feet from the average grade. As with mezzanines, this 'basement' level is not considered a 'floor' or 'story,' but it helps to achieve an eight-level building that’s in the range of 85 feet high.
Whether a designer is considering wood because of cost, aesthetics, low carbon footprint or any of its other benefits, it's useful to recognize that building codes recognize wood's structural performance capabilities in a broad range of applications, from the light-duty repetitive framing common in small structures to the larger and heavier framing systems used to build arenas, schools and other large buildings. Engineered wood products such as CLT also offer exceptional stability and strength and have made wood a viable alternative to steel or concrete in many applications.
Materials In Action Matter
In building operation and end of life, wood continues to prove its value as a sustainable building material. It is a strong, durable, natural insulator that can be designed to perform well under fire conditions and to withstand seismic forces. It has less embodied energy than steel or concrete. It lends itself to recycling and reuse without significant energy input. It continues to store carbon absorbed by the trees during their growing cycle—keeping it out of the atmosphere for the life of the building, or longer if reclaimed and used elsewhere. Wood waste made into viable products can help spur the economy in rural areas.
This is the second of a three-part series documenting the environmental footprint of wood, concrete, and steel. The third and final article, A Natural Choice, will cover how these materials factor into green design and high-performance buildings as well as how green design projects are currently defined.
| Endnotes | |
| 1.) | Survey on Actual Services Lives for North American Buildings, J. O'Connor, Forintek (now FPInnovations) |
| 2.) | Utilization of Harvested Wood by the North American Forest Products Industry, Dovetail Partners, Inc., 2012 |
| 3.) | Wood Can Help Control Indoor Relative Humidity, FPInnovations (then Forintek), 2004. |
| 4.) | According to the National Fire Protection Association, property loss from fire was estimated at $11.7 billion in 2011. http://www.nfpa.org/research/fire-statistics/the-us-fire-problem |
| 5.) | Southern Pine Use Guide, Southern Forest Products Association, http://www.raisedfloorlivingpro.com/pdfs/publications/Southern-Pine-Use-Guide.pdf |
| 6.) | Superior Fire Resistance, American Institute of Timber Construction, http://www.aitc-glulam.org/shopcart/Pdf/superior%20fire%20resistance.pdf |
| 7.) | The January 17, 1994 Northridge Earthquake, an EQE Summary Report, http://www.lafire.com/famous_fires/1994-0117_NorthridgeEarthquake/quake/00_EQE_contents.htm |
| 8.) | Forestry Innovation Investment, China |
| 9.) | Wisconsin Ready Made Concrete Association, http://www.wrmca.com/mid-high-rise-structural-concrete-framing.html |
| 10.) | NBS, http://www.thenbs.com/topics/constructionproducts/articles/ achievingThermalComfortInTimberFrameBuildings.asp |
| 11.) | Thermal Performance of Light-Frame Assemblies, Canadian Wood Council, http://cwc.ca/documents/IBS/IBS5_Thermal_SMC_v2.pdf |
| 12.) | Steel vs. Wood Long-Term Thermal Performance Comparison: Valparaiso Demonstration Home, NAHB Research Center, http://www.huduser.org/portal/publications/destech/steelval.html |
| 13.) | US Environmental Protection Agency, http://www.epa.gov/wastes/conserve/imr/cdm/index.htm |
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The reThink Wood initiative is a coalition of interests representing North America’s wood products industry and related stakeholders. The coalition shares a passion for wood and the forests it comes from. Innovative new technologies and building systems have enabled longer wood spans, taller walls, and higher buildings, and continue to expand the possibilities for wood use in construction. www.rethinkwood.com |
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