Paul C. Hutton
Published 3 years ago.
About a 4 minute read.
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The ability to not only eliminate greenhouse gas emissions, but actually sequester carbon, would transform buildings from net negative to net positive entities. Here, we examine several approaches making this possible.
By now, we know that the global design and construction industry is responsible
for approximately 39 percent of total greenhouse gas
(GHGs). That is subdivided into 28 percent for all the energy used to heat,
cool, ventilate, light, and power our buildings; plus, another 11 percent to
mine, extract, harvest, process, manufacture, fabricate and transport all the
materials used to construct them. Put more simply, that’s 28 percent for
building operations and 11 percent for the embodied
of construction materials.
As the design and construction industries work to reduce both of these
significant contributors to climate change, the question arises as to whether
buildings can actually sequester carbon. Sequestering carbon would transform
buildings from net negative to net positive environmental impacts. Below we
examine several approaches making this possible.
As recent advances in wood technology have enabled architects and engineers to
make wood buildings taller than ever, many are investigating the use of much
more wood in the buildings they design. While glue-laminated (glulam) timber and
parallel strand lumber (paralam) have been in use for a long time as columns and
beams, an entirely new generation of products referred to as cross-laminated
timber (CLT) is now available in many markets. Unlike earlier versions of
engineered lumber, CLT is available in large sizes, and can be used as entire
walls and floors.
Building Codes have followed this trend; and the 2021 version of the
International Building Code (used throughout the United States) allows
timber buildings up to 18 stories. Elsewhere in the world, even more ambitious
wood construction is allowed. Some recent examples of tall timber construction
— 7-story, Minneapolis, MN, completed November 2016
Carbon12 condominium building — 8-story,
Portland, OR, completed in 2017
Brock Commons Tallwood
18-story, Vancouver, BC, completed 2017
Kajstaden Tall Timber
— 8.5-story, Sweden, completed 2019
— 18-story, Norway, completed 2019
— 40-story, Australia, to be completed 2025
Substituting wood for steel and concrete has the potential to greatly reduce the
GHG impact of buildings, especially if the wood structure can be deconstructed
at the end of its life and reused.
The global concrete industry, if it were aggregated as a country, would be
responsible for more GHG emissions than all but two other countries — the US and
China. The manufacturing and processing of concrete and its essential
ingredient — cement — are extremely energy intensive and emissions-heavy. As a
result, concrete manufacturers are actively pursuing methods to reduce the GHG
A few promising directions include:
Waste CO~2~ from industrial operations can be injected directly into concrete.
Once injected, the CO~2~ is transformed into a mineral, so it is never
released back into the atmosphere as CO~2~, even if the concrete is pulverized
for re-use. The resulting concrete is also stronger than traditional concrete.
One company, called CarbonCure, is active in the
field and claims that its technology could reduce up to 700 megatonnes of global
CO~2~ emissions annually.
Hempcrete is a composite material that combines the inner woody core of hemp
plants with lime binders. It is approximately one-eighth the weight of concrete
and is used where concrete block might be used as an exterior or interior wall.
Unlike traditional poured-in-place concrete or concrete block, however; it is
non-structural and must be combined with other frame elements such as wood or
Much concrete is now recycled after the useful life of the building or structure
is compete. This has the advantage of eliminating the environmental devastation
due to mining raw materials, but it still takes a tremendous amount of energy to
demolish concrete and crush it into useful aggregate. Only about 2 percent of
the embodied energy of the original concrete remains with this approach.
Grounds are often overlooked opportunities to sequester carbon in the built
environment. The ability of landscaping to sequester carbon varies widely
depending on the approach to plants and hardscaping (sidewalks, drainage
structures, furnishings, etc). Minimizing concrete and other high-GHG materials
such as steel in favor of lower-intensity materials — such as gravel for paths
and wood for structures — can make a significant difference in the initial
embodied carbon of a landscape area.
Plants absorb CO~2~ and release oxygen, which benefits the overall carbon
balance of a property. More woody plants on a property help with absorption of
CO~2~ over time. Surprisingly, expanses of bluegrass lawn are not beneficial
for carbon sequestration — and, in fact, are usually net-carbon emitters due to
the energy intensive fertilization, mowing, and other maintenance required for
With careful attention to material selection, maintenance procedures and plant
specification, landscaped areas can become net absorbers of CO~2~ within a few
years after initial construction.
As designers push to decarbonize the built environment and actively remove
carbon from the atmosphere, they will increasingly embrace these strategies and
more. Reaching net-zero emissions by the year 2040 or 2050 will require
substantial changes in how we design and build, with sequestration increasingly
necessary to achieve that elusive goal.
Published Dec 2, 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.