Mass Timber Punches Above Its Weight In Reducing Buildings’ Embodied Carbon Footprint

The built environment can be a behemoth when it comes to contributing to climate change, but the reality is not set in stone. Advancements in the production of building materials and substituting greener components can make a difference.

Buildings generate almost 40% of annual global greenhouse gas emissions, according to WoodWorks Regional Director Chelsea Drenick, who spoke at a Home and Environment webinar hosted by the Housing Action Coalition on Earth Day.

WoodWorks, a nonprofit organization that provides free assistance for designing wood buildings, is part of a push to focus more on the embodied carbon emissions of buildings beyond just the operational carbon emissions, which has historically generated more action toward reduction.

“There's a huge opportunity for us as building designers to improve the way buildings are built and contribute to the solutions to greenhouse gas emissions,” DCI Engineers Senior Project Manager Robin Landis said. “Reducing operational carbon cannot be the only solution. It must go hand-in-hand with reducing embodied carbon. 

Operational energy can be reduced over time with energy-efficiency renovations and the use of renewable energy; however, embodied carbon is locked into the atmosphere as soon as the building is built, making it imperative to tackle the issue as quickly as possible, Landis said.

The urgency is in part due to the timeline of emissions. Although operational carbon surpasses embodied over the lifetime of a building, it takes 17 years for operational carbon to surpass embodied carbon, Drenick said. This means that efforts to reduce embodied carbon can have a robust and immediate impact in combating climate change.

One of the primary ways of addressing the embodied carbon in buildings is to use different materials. Concrete has gained a reputation for having a high carbon footprint and for good reason. If cement were a country, it would be the third-largest carbon emitter in the world just behind China and the U.S., Landis said. This is due to the large amount of energy used to create the building material.

However, new types of concrete are being developed that are viewed as more sustainable. For example, Portland-limestone cement has a lower environmental impact because its production is less energy-intensive, according to Landis.

Provided that it has been sourced from a sustainably managed forest, wood is the foremost building material for reducing greenhouse gas emissions because it is 40% carbon by mass, Drenick said. Carbon that was previously circulating in the atmosphere was sequestered in the tree during its growth and instead of dying, decaying and releasing that carbon back into the atmosphere, the tree can be converted into wood and used as a building material — and as a carbon sink.

Although there are concerns about tree preservation that stem from unsustainable logging practices, Drenick said that studies have shown wood used as a building material can actually increase the number of trees in a forest. Data from The Forest History Society shows that net tree growth in the U.S. has been steadily outpacing tree removal since 1952.

“Wood is the only truly renewable resource that we build with — there is only a finite amount of steel and concrete materials in the world,” Landis said. “Wood can only be as sustainable as the process used to harvest and manufacture the product. To minimize the amount of embodied carbon associated with wood construction, it's incredibly important to use materials sourced from climate-smart forests. Another consideration when choosing wood suppliers is to look for locally harvested and manufactured products.”

Mass timber is a prefabricated type of building material that uses smaller pieces of lumber that combine to form large beams and panels. This differs from heavy timber, in which achieving a large column for a building means finding a tree matching the size of the desired effect. Instead, with mass timber, the wood pieces are laminated together using adhesives, nails or screws.

Cross-laminated timber is a mass timber product that can be used in place of concrete due to its strength, according to Landis, who cited less construction site waste as one of several benefits of mass timber overall.

Use of mass timber is becoming more widespread. WoodWorks has tracked over 1,000 mass timber buildings since 2013. On July 1, California code will allow for mass timber buildings of up to 18 stories. Because mass timber relies on the harvest of small diameter trees, it is seen as benefiting wildfire mitigation because it helps thin the forest of less mature trees, Drenick said. She cited big tech companies like Microsoft, Google and Facebook as all having mass timber projects currently underway in the Bay Area.

Despite not being renewable, steel is becoming a more sustainable building material due in part to its high recyclability. However, the carbon emissions reductions are dependent on the manufacturing of steel being powered by renewable energy versus fossil fuels.

“The biggest new innovation in the steel industry is the electric arc furnace,” Landis said. “This process uses an electrical current to produce molten steel instead of utilizing fossil fuels associated with traditional methods. This process greatly reduces embodied carbon associated with steel production and has become increasingly more common in the industry."