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
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.
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.
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
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.
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.
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
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.
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.
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
Kevin Rodenkirch and Benton Johnson are with Skidmore, Owings & Merrill, LLP
- Annual Estimates of the Population for the United States, Regions, States, and Puerto Rico, U.S. Census Bureau, Washington, 2013.
- Urban and Rural Areas 2009, United Nations, New York, 2009.