What Developers Need to Know About Mass Timber

A new tool helps to improve the accuracy of carbon emissions assessments.

Indications are that the use of mass timber will continue to grow, especially for low- to mid-rise buildings. According to Business Research Insights, the global mass timber construction market generated $3.2 billion in 2024, a number projected to nearly triple by 2033. As the construction industry’s emissions came under more scrutiny, mass timber’s lower embodied carbon became an attractive alternative to concrete and steel construction.

However, a 2023 report from the World Resources Institute suggested that mass timber is not inherently carbon neutral, largely due to emissions from the harvesting process that aren’t accounted for in standard life cycle assessments (LCAs). Echo and Hugo, the sustainability and research teams at architecture and design firm Corgan, undertook a joint research initiative to gain a more comprehensive understanding of the carbon emissions associated with mass timber production.

The Bigger Picture

Mass timber is viewed as carbon neutral because trees naturally sequester carbon over their lifetimes. However, when that carbon is re-released — via decay or burning — instead of making it to the building stage, it increases the emissions associated with the material. To obtain the most accurate emissions calculations for a building, it is important to include biogenic carbon that is inherent in the harvesting, processing and transportation of the materials used.

These emissions, which can be significant for mass timber because of the logging process, have not previously been included in LCAs. When trees are harvested for lumber, around 25% of the tree’s biomass is left in the forest as slash — twigs, bark and other unusable fragments of wood. Next, the trees are processed, sawed, dried and trimmed. Ultimately, only 35% of what is cut down in the forest makes it to the building stage.

To improve the accuracy of emissions calculations for mass timber, Corgan has developed a tool that accounts for three common slash management methods for seven of the most commonly used species of trees. Designers, specifiers and other architecture, engineering and construction professionals can use this calculator (available at corgan.com/MTcarboncalculator) to refine their carbon emissions estimates for mass timber buildings.  

What’s Left Behind?

When considering mass timber construction as a sustainable alternative building material, it is important to assess the slash management practices, wood species selection and transportation impact.

The most common slash management practices are pile burning, mastication and site composting. While each has pros and cons from a forestry perspective, they also have very different impacts on carbon emissions from the designer’s and builder’s perspective:

• Pile burning releases carbon very quickly, resulting in a 50% to 80% increase in carbon dioxide equivalent (CO2e) release compared with current industry estimates. 
• Mastication was the clear winner overall, with emissions increasing only 3% to 5% from baselines. 
• Site composting sits in the middle, with emission increases ranging from approximately 25% to 45% for most species, the exception being western red cedar, which saw an increase of just over 1%.

Material transportation also has a large impact on the emissions associated with mass timber, so it is important for builders and designers to consider which wood is being used in the project and, when possible, to choose alternative local options that are closer to the project site. While locally sourced timber is often preferable from a carbon standpoint, it may be more expensive or less available, or a client may have a specific wood in mind. Corgan’s carbon calculator offers a simple way to illustrate the environmental impact of that choice and help evaluate alternative options.  

How Mass Timber Stacks Up

When considering embodied carbon, mass timber still comes out on top compared with traditional steel and concrete buildings. The mass timber calculator shows that even in the worst-case scenario — pile burning — it remains a carbon-sequestering material. Depending on the slash management approach, mass timber offers embodied carbon emission savings ranging from 100% to 340% compared with reinforced concrete.  

Beyond sustainability, the use of mass timber can benefit project timelines, with a 10% to 20% savings in scheduling, because the panels can be prefabricated. The cost of mass timber currently ranges 6% to 26% higher than typical concrete and steel construction methods, although costs are projected to decrease as use increases.

With these factors in play, mass timber construction is a worthwhile consideration for new low- to mid-rise buildings, especially for clients who want to focus on reducing embodied carbon and increasing the sustainability of new construction. In addition to offering embodied carbon benefits, timber and wood are generally accepted as an aesthetically desirable material for end users. This is directly associated with biophilic design principles and the positive impact of tactile natural materials in the built environment on mental and physical well-being.

The industry is still in the early stages of what may become a mass timber boom, but the promise of this construction modality is already evident in large projects such as the 400,000-square-foot timber roof at Portland International Airport in Oregon and in multifamily and commercial developments such as Ascent MKE, a 25-story apartment building in Milwaukee.

Accurate Carbon Assessments

As mass timber use grows, having a big picture understanding of its true emissions will be integral to making informed, cost-effective and environmentally responsible decisions. Corgan’s calculator enables designers to:

• Quantify hidden CO2e emissions more accurately 
• Evaluate trade-offs between species, location and carbon impact
• Support material choices that balance sustainability and cost
• Improve transparency and collaboration with suppliers and contractors

Ultimately, this research empowers developers to make smarter decisions in the early design phase that reduce embodied carbon later on. As sustainability continues to be a vital factor in new construction projects, accurate carbon assessments are paramount. 

Varun Kohli is the director of sustainability at Corgan. Mahdi Afkhami, Ph.D., is an environmental designer researcher at Corgan.

Terms to Know Mass timber: A construction modality that uses a wood product, usually made from multiple wood panels nailed or glued together for extra strength, instead of steel or concrete. It is growing in popularity due to its lower carbon footprint. Embodied carbon: The greenhouse gases released during the extraction, production and transportation of materials used in construction. Biological carbon sequestration: The ability of natural ecosystems to store atmospheric carbon. Carbon can be stored in plants, soil, wetlands and the ocean. For the purpose of this research, Corgan focused on carbon sequestration of trees. Biogenic carbon: The result of sequestration, it is the carbon stored in biological materials. Biogenic carbon is stored during the life of the tree and released when it is destroyed. CO2e: Carbon dioxide equivalent; a measurement used to compare the emissions of any greenhouse gas based on its global warming potential. Cradle-to-site: Stages A1 through A4 in a life cycle assessment, starting where the raw material is harvested, transported, manufactured into a usable product, and transported again to the construction site. Slash: The material (branches, twigs, bark) left behind during mass timber harvesting — approximately 25% of the mass of the timber.

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