Paul C. Hutton
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The tremendous work to reduce operational carbon from buildings in recent years can be seen in the rise of net-zero energy buildings. But without a
comparable focus on reducing embodied carbon in construction materials, that work will not lead to the hoped-for mitigation of climate change.
The built environment is responsible for more greenhouse gas
(GHGs) than any other sector of the economy — more than transportation,
agriculture and industry. This situation needn’t be so, as we have the means to
greatly reduce or eliminate operational carbon from the building sector. We are
making substantial progress in developing methods to reduce the embodied carbon
Operational carbon refers to the total from all energy sources used to keep our
buildings warm, cool, ventilated, lighted and powered. Typical energy sources
for this purpose are electricity and natural gas, with occasional contributions
from fuel oil, propane and wood. The “carbon” part of operational carbon is a
stand-in for all the GHGs released from these many energy sources and is the
total of all GHGs released by them. You will occasionally see the abbreviation
“CO2e” which signifies carbon dioxide equivalent. When CO2e is calculated, GHGs
that have more greenhouse potential than CO2 are over-weighted in proportion to
their impact (methane, for example).
Embodied carbon is the total emissions of GHG from all energy sources used to
mine, log, harvest, extract, process, manufacture and transport to the
construction site; and assemble the thousands of materials that go into a
typical building. As with operational carbon, we measure this using CO2e. In our
we mentioned that operational carbon is approximately 28 percent of global and
US GHG, while embodied carbon is another 11 percent.
The regulatory environment of the last two decades, as applied to design and
construction through building codes, has become ever more stringent. For
example, the International Building Code (IBC) used in the US has
required a 50 percent decrease in energy use in new buildings since 2000. That
decrease seems poised to continue and may reach net-zero
— a condition in which a building or property produces as much renewable energy
as all the energy it consumes in the course of a typical year — by 2035 or so.
While the IBC is leading to greater energy efficiency for new buildings and is
reducing GHG emissions from new construction, it ignores two important factors:
First, existing buildings are only required to be upgraded when undergoing
substantial renovation; it is possible for inefficient older buildings to remain
in that condition indefinitely. We’ll examine this issue in greater depth in a
future article. The second gap in the building code, used by designers and
contractors, is that it completely ignores embodied carbon.
Architects and engineers have recently begun to develop tools to track and
calculate the embodied carbon of their designs. Several different software
platforms are now commercially available and are not prohibitively expensive.
Using these platforms, a clear picture of embodied carbon is emerging. A few key
The structure of a building is responsible for approximately 50 percent of a
building’s total embodied carbon;
The exterior envelope of a building is responsible for another 30 percent;
The interior of a building is responsible for the remaining 20 percent; and
Concrete is the single most impactful material used in construction. The
global concrete industry — if it were its own country — would be the
world’s third-largest GHG
China and the United States.
Architects have recently established voluntary targets for embodied carbon
reductions, through the Architecture 2030
program. Those targets are an immediate reduction of 40 percent, then 65 percent
reduction by 2030, and zero emissions from materials by 2040. Achieving these
results will not be easy and will require may innovations in the design process
and materials technology.
A tremendous amount of hard work has gone into reducing operational carbon from
building operations in the last several years. Net-zero energy buildings are the
visible symbols of that effort. Without a new and comparable focus on reducing
the embodied carbon of construction materials, that work will not lead to the
hoped-for reduction in climate change that GHG emissions cause.
Published Nov 18, 2020 7am EST / 4am PST / 12pm GMT / 1pm CET
Paul Hutton, FAIA, NCARB is a LEED Fellow, and Chief Sustainability Officer at Cuningham Group Architecture, Inc.
This article, produced in cooperation with the Sustainable Brands editorial team, has been paid for by one of our sponsors.