Learn more about biogenic and embodied carbon, and wood’s impacts on forest health. Read this CEU from our partner, Think Wood:
Wood products have less embodied energy, are responsible for less air and water pollution, and have a lighter carbon footprint than other commonly used building materials. Wood can contribute to a building’s energy efficiency and biophilic design, and is durable, adaptable and re-usable. Explore the sections below for details on embodied and stored carbon, life cycle assessment (LCA), biophilia, and more.
Less Embodied Carbon + Stored Carbon
How do we build sustainably and achieve carbon-reduction goals while also meeting the housing and infrastructure needs of a growing population? One answer is more wood buildings.
According to Architecture 2030, buildings are responsible for nearly 40% of annual global greenhouse gas (GHG) emissions. Embodied carbon—i.e., greenhouse gases emitted during the manufacture of materials and construction of buildings—accounts for about 11%, and most of these (9%) are related to the use of concrete, iron and steel.1 In a typical non-wood building, it takes approximately 17 years to pay back the energy debt.2
Wood products have low embodied carbon
They’re usually less energy intensive to manufacture than steel or concrete, and most of the energy comes from renewable biomass (e.g., bark and other residual fiber) instead of fossil fuels. Substituting wood for fossil fuel-intensive materials reduces embodied carbon.
Wood buildings store carbon
As trees grow, they absorb carbon dioxide (CO2) from the atmosphere, release the oxygen (O2) and incorporate the carbon into their wood, leaves or needles, roots and surrounding soils. When trees are manufactured into products, they continue to store the carbon. (Wood is 50% carbon by dry weight.3) In the case of buildings, the carbon is kept out of the atmosphere for the lifetime of the structure—longer if the wood is reclaimed and manufactured into other products or reused.
“Every year, 17,000 buildings constructed with other materials could be built with wood. In most cases, it costs about the same to build with wood, and yet the environmental benefits are significant. Building with innovative wood products from sustainable, properly managed forests is a relatively easy way to alleviate a sizable amount of U.S. carbon emissions.”
– Jennifer Cover, President and CEO, WoodWorks, Testimony to the Committee on Energy and Natural Resources, United States Senate
The forest/carbon cycle helps keep carbon out of the atmosphere
When forests are sustainably managed (as they are in North America), the cycle begins again. Carbon from the harvested forest remains stored in buildings as the forest starts regenerating and once again begins absorbing CO2. Strong markets for wood products also provide an incentive for landowners to invest in forest thinning and other landscape restoration efforts that promote forest health and reduce the risk of wildfire—another significant contributor of CO2.
1 Architecture 2030
2 Building a Global Carbon Sink, Alan Organschi, Gray Organschi Architecture
Evaluate the life cycle impacts of your material choices.
Learn about tools for comparing embodied carbon or up-front greenhouse gas emissions of designs with different structural systems. Read this expert tip
Life cycle assessment (LCA) is an internationally recognized method for measuring the environmental impacts of materials, assemblies or buildings over their lifetimes—from extraction or harvest of raw materials through manufacturing, transportation, installation, use, maintenance, and disposal or recycling. It allows design professionals to compare different building designs based on their environmental impacts and make informed choices about the materials they use.
LCA is replacing the prescriptive approach to material selection, which assumes that certain prescribed practices (such as specifying products with recycled content) are better for the environment regardless of the product’s manufacturing process or disposal.
LCA studies consistently show that wood outperforms other materials in terms of embodied energy, air and water pollution, and carbon footprint—and more project teams are incorporating these studies into their pre-design process.
The wood industry has also been an early adopter of Environmental Product Declarations (EPDs), which are a user-friendly way to communicate information gathered through LCAs.
Read more about LCA and EPDs in the Think Wood CEU, How to Calculate the Wood Carbon Footprint of Buildings.
Five-Story Mass Timber Office: Case Study + LCA
Crescent Real Estate has found that sustainable architecture, including buildings with a lighter carbon footprint, appeals to a wide range of tenants. Working with Oz Architecture, KL&A Engineers & Builders, and Adolfson & Peterson Construction, Crescent made sustainability a priority for Platte Fifteen, a five-story CLT office building in Denver. It’s one of the first projects to have both a case study on its design and construction and an in-depth LCA.
In terms of operating energy, wood has the advantage of low thermal conductivity compared to steel and concrete.1 As a result, wood buildings are easy to insulate to high standards.
While any wood structural system can be designed to achieve a tight building envelope, the precise manufacturing of mass timber systems can provide exceptional air tightness. (The added aspect of dimensional stability also ensures that the building remains airtight over time.) Wood is also proving to be a good choice for designers who want to meet the Passive House (Passivhaus) standard or create net-zero energy or net-zero carbon buildings. Read about 11 E Lenox in Boston, a seven-story mass timber Passive House project from design-build firm Haycon and Monte French Design Studio.
Because many factors have a greater influence on energy efficiency than the choice of structural material, a more relevant point for many designers is that wood building systems have low embodied carbon—i.e., greenhouse gases emitted during the manufacture of materials and construction of buildings. LCA studies consistently show that wood outperforms other materials in this area.2
1 The American Wood Council answers the question, What is the thermal conductivity of wood and how does it compare to other materials?
2 A Synthesis of Research on Wood Products & Greenhouse Gas Impacts, 2nd Edition – R. Sarthe, J. O’Connor, FPInnovations, 2010; Building with Wood = Proactive Climate Protection, Dovetail Partners, Inc.