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The Build Carbon Neutral calculator
captures the effect of design decisions and estimates the carbon
that will be released in the construction of a particular
facility.
 The green
building evolution continues. A world awash in ratings, standards,
and criteria now has a new player. Although several industry
systems address operating energy, none simply quantify embodied
energy. To fill the gap, a highly collaborative effort produced the
Build Carbon Neutral (BCN) calculator earlier this year. Led by
Seattle-based Mithun, BCN captures the effect of design decisions
and estimates the carbon released in the construction of a
particular facility.
Consider the importance: by 2030, approximately 75 percent of the
U.S. building stock will be new or renovated, and 18 percent of the
lifetime carbon emissions from each building will be released in
its construction. BCN does the math by assessing the primary
structural system, soil displaced by the structure, and other
disturbed landscaping.
Mithun first came to work on the calculator while developing a
master plan for the Lloyd District in Portland, Ore., which
received an AIA Top Ten Green Projects award in 2005. The design
team decided that an embodied energy profile would help complete
the neighborhood-level plan and began to research the underlying
effects of various design options. Some complex lifecycle
assessment (LCA) tools exist but more data were needed to gauge the
true construction allocation.
Sean Cryan, an associate principal at Mithun, led the effort, along
with colleagues Critter Thompson, an ecologist, and Deb Guenther, a
landscape architect. Mithun has also completed three years of
footprinting its internal carbon profile.
In early 2006 the team started working with Lindsay Lawrence, a
University of Washington grad student, on an excavation study. This
set the stage for the calculator by measuring the carbon released
in clearing various amounts of dirt. Additionally, Mark Simmons and
Heather Venhaus from the Lady Bird Wildflower Center contributed
valuable vegetation information regarding carbon sequestion and
release.
Moving to the building itself, Pliny Fisk III of the Center for
Maximum Potential Building Systems, and Craig Jones of the
University of Bath’s Department of Mechanical Engineering
provided expertise on carbon intensity ratios. These data quantify,
for example, how much carbon is released in extracting, refining,
transporting, and installing a pound of steel used in construction.
Attached to these are percent contributions of various building
components on the overall embodied carbon profile. For instance,
the primary structure—steel, wood, concrete—is
responsible for about 12 percent of the embodied carbon, while
interiors contribute 15 percent of the footprint.
The BCN team has compared results with other LCA tools and found
good correlations, and all tests have remained within a 25 percent
variance. Cryan offered that “it’s almost more important
to get a sense of relative impact than to calculate the exact
fraction of a metric ton [of carbon].”
More data and features will be added in subsequent phases, however.
Specifics on above-ground vegetation, interiors, and furniture,
furnishings and equipment will soon be included, allowing users to
fine-tune their projects’ embodied footprint. Cryan also hopes
that the tool will eventually provide users with suggestions for
carbon reduction design strategies based on input parameters.
Jared Silliker is a senior analyst at the Cadmus Group, an
environmental consulting firm. His focus is on energy efficiency,
and he works with the architecture community to encourage high
performance building designs.
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