Over the past decade, sustainable design requirements have begun to make their way into building codes. However, as this shift has occurred, it has become apparent that the codes’ prescriptive requirements often limit the use of high performance sustainable designs that incorporate strong technical solutions.

In general, building codes outline today’s standards, but don’t flexibly accommodate future design innovation. The most forward-thinking sustainable design solutions, therefore, will go no further than the design development table – to both incorporate them into a project and meet building codes is often too costly, too redundant, or too cumbersome.

The proposed use of mass timber to construct mid- and high-rise buildings is a perfect example of a sustainable solution that cannot easily be realized until building codes change. Most prescriptive codes prohibit the use of heavy timber in construction that exceeds certain heights, number of floors, and/or floor areas.

Building timber towers, however, would help mitigate growing population and environmental degradation concerns. Since 1990, the United States’ population has grown by approximately 3 million people per year.1 The largest centers of growth within the U.S. are metropolitan areas; worldwide, urbanization in some of the fastest growing regions is happening at a far greater rate.2

Housing will drive a large portion of future construction, and it is important that the planning that goes into it – including the standards set within the building industry – provides buildings that will be safe, livable, efficient, and sustainable. One must be critical of how buildings are designed, constructed, and operated going forward. This includes reassessing the stipulations of building codes.

Beyond building codes, there are a number of standards and rating systems that can help to guide this process, including the "2030 Challenge” (see http://www.architecture2030.org). The 2030 Challenge promotes better design strategies and the use of on- and off-site energies in order to achieve operational carbon neutrality in buildings by 2030. However, it doesn’t consider buildings’ embodied carbon footprints, and designers need to consider embodied carbon footprints because they cannot be improved over the life of a building.

Virtually all materials and systems have a net positive carbon footprint. Wood is the exception to this rule: it is approximately 50% carbon by weight and also acts as a carbon sink, absorbing carbon emissions from the surrounding environment. This is what makes mass timber such an appealing structural material for mid- and high-rise residential construction.

When used in lieu of traditional structural materials, such as concrete or steel, mass timber would significantly reduce a mid or high-rise building’s embodied carbon footprint. When these savings are combined with operational carbon savings, a mass timber building would most likely achieve far greater carbon footprint reductions than a comparable building made from structural concrete and/or steel.

Unfortunately, current building codes restrict the height of timber structures when categorized as heavy timber structures. They also prohibit the use of combustible structural materials when structures are classified as high-rise buildings. To make solutions like timber towers possible, building codes must shift from being prescriptive to performance-based.

The path to code compliance through performance-based design needs to become a more widely recognized and viable option for designers. If the industry can accept the fact that innovation comes in many forms, not all of which will fall within prescriptive requirements or traditional means of design and construction, the doors will be open to incorporate the best and most innovative high performance systems, materials, and applications into real buildings. This will allow the industry to not only meet current goals, but continue to exceed them well into the future. Design development taking place across the globe indicates that high performance design possibilities are nearly limitless. More performance-based building codes will let them go from research to reality.

Kevin Rodenkirch and Benton Johnson are with Skidmore, Owings & Merrill, LLP


References:

  1. Annual Estimates of the Population for the United States, Regions, States, and Puerto Rico, U.S. Census Bureau, Washington, 2013.
  2. Urban and Rural Areas 2009, United Nations, New York, 2009.