CNC Report 08.26.24 8.5x11 - Flipbook - Page 124
02 MASS TIMBER
MASS TIMBER
The upfront embodied carbon of timber is not negative and can be higher than steel or concrete
construction. However, wood construction has the advantage after the whole life cycle assessment.
For example, the full wood system had a significantly lower embodied carbon cost, with an
approximate 45% reduction per square meter compared to a concrete system.
Carbon Sequestration
Accounting for the carbon sequestration of the timber can offset up to a value greater than the
embodied carbon of the entire structure. However, this must be carefully studied as the sourcing of
the timber significantly affects the potential for biogenic storage. Biogenic storage is carbon stored in
biological materials like wood. During the growth of bio-based materials, carbon is stored. Using these
materials in building products retains the carbon until the end-of-life of the building. For example, the
graph shows cumulative production data for a similar building, including three scenarios for wood
components. In wood scenario 1, sequestration causes a small temporary period of negative carbon
emissions. This lasts while the building is in use and ends with its demolition. If the structure had a one
hundred year lifecycle, it would be carbon negative for half of its useful life.
It is estimated that one cubic meter of mass timber sequesters one metric ton of carbon dioxide. By
contrast, it is estimated that every ton of manufactured cement produces about 0.47 tons of CO2,
and 0.6 tons of CO2 is produced for every ton of manufactured iron (Mass Timber Institute, University
of Toronto). Using mass timber as an alternative or supplemental structural element to steel and/or
cement easily reduces the environmental impact of a project.
Strength
Being only a fraction of the density of concrete and steel with comparable strength ratings means
mass timber products are lighter and have higher strength-to-weight ratios. This allows for smaller
building foundations whilst supporting loads comparable to steel components.
Cost Advantages of Mass Timber
While costs will vary depending on the region, application, size, and scope of each project, a 2021
study by LPA Design found the cost of CLT to be around $10 more per square foot than a conventional
steel and concrete building in a commercial application. However, various financial benefits can offset
the initial cost:
• Mass Timber building components can be mass-produced and pre-assembled off-site before site
delivery, reducing development lead times and labor costs.
• CLT components weigh about 30% less than concrete equivalents, lowering transportation costs,
creating smaller building foundations due to the smaller load, and decreasing site-prep and
machinery.
Fire Resistance
While wood is perceived as flammable, mass timber is inherently fire-resistant. When exposed to fire,
the outer surface chars, acting as insulation and delaying the effects of heat on the structural core,
thus slowing the fire’s progression. External tests with CLT panel walls have seen it withstand 1,800
degrees Fahrenheit heat for over three hours, well beyond the two-hour rating required in building
codes.
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