{"id":212865,"date":"2025-10-08T08:48:18","date_gmt":"2025-10-08T12:48:18","guid":{"rendered":"https:\/\/www.constructionspecifier.com\/?p=212865"},"modified":"2025-10-28T09:12:15","modified_gmt":"2025-10-28T13:12:15","slug":"mass-timber-hidden-carbon","status":"publish","type":"post","link":"https:\/\/www.constructionspecifier.com\/mass-timber-hidden-carbon\/","title":{"rendered":"Mass timber\u2019s hidden carbon: The role of slash management"},"content":{"rendered":"
\"A<\/a>
Rendering courtesy Corgan<\/em><\/figcaption><\/figure>\n

The use of mass timber in construction, which is gaining in popularity, is commonly thought to be carbon neutral\u2014but is it? Corgan\u2019s Research and Development group, Hugo, alongside the firm\u2019s Sustainability team, Echo, conducted peer-reviewed research focused on identifying emissions in mass timber that result from harvesting. Explore slash management and why mass timber remains a more sustainable option than concrete or steel when considering carbon emissions.<\/p>\n

A false positive<\/h2>\n

In the industry-wide effort to reduce its carbon footprint, AEC practitioners are paying close attention to embodied emissions, the carbon (and other greenhouse gas) emissions associated with the whole lifecycle of the materials used. Since these embodied emissions account for 20 percent of a building\u2019s total energy use over its lifetime, they are an important target for minimizing the environmental impact of new construction and renovations. Mass timber has gained attention as a more sustainable alternative to standard concrete and steel construction for low to mid-rise projects. This is because mass timber is seen as being carbon-neutral, since trees naturally sequester carbon during their lifetimes. Due to the interest in this seemingly sustainable building material, the global demand for wood products is expected to quadruple by 2050.<\/p>\n

However, a 2023 report from the World Resources Institute states there are emissions associated with mass timber that are not considered, particularly as it relates to timber harvesting practices. Corgan\u2019s research seeks to fill this gap in understanding by identifying and estimating the emissions that are not typically accounted for in the harvesting of timber\u2014the slash left behind on the forest floor and the way these materials are managed. The resulting report identifies tree species typically used in mass timber products, applies three common scenarios for managing the slash to determine the associated CO2e emissions, analyzes the impact of the transport of raw material on its embodied carbon, and makes recommendations to designers on how to manage this effectively. The research also resulted in the development of Corgan\u2019s Mass Timber Carbon Calculator,1<\/sup> a free-to-use tool that enables AEC professionals to easily improve their carbon emission estimates for mass timber projects.<\/p>\n

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Figure 1: This graph compares the embodied carbon of the structure for concrete, mass timber with biogenic values, and mass timber with biogenic values that also account for slash emissions in the composting scenario. As shown, both mass timber scenarios result in negative values, indicating carbon sequestration and reinforcing mass timber as a sustainable choice even when slash emissions are considered. Illustrations courtesy Corgan<\/em><\/figcaption><\/figure>\n

Status quo and study scope<\/h2>\n

To begin, the study helps understand what is currently missing in the timber harvesting process in lifecycle assessments (LCAs). From extraction through processing, around 65 percent of a tree\u2019s initial mass is lost\u2014to slash in the forest, to shavings and wood chips in the sawmills, and to shrinkage and trimming allowance in the final wood product\u2014meaning only 35 percent of what is cut down ends up in the building.<\/p>\n

Of this, it is estimated that about 25 percent of the tree\u2019s mass is lost to harvest residuals\u2014the twigs, bark, and other small pieces of wood left behind that are known as slash. Since the carbon stored in slash is eventually released back into the atmosphere, these residuals represent a significant source of emissions that are not generally accounted for in mass timber buildings. However, the way slash is managed can play a significant role in the level of emissions. Corgan\u2019s research includes three common slash management practices:<\/p>\n