Mass timber: reducing carbon in the built environment

The role of mass timber construction in supporting global decarbonisation is in the spotlight in North America, particularly following the easing of building control limitations.

Offering proven efficiency across both construction schedule and cost, as well as drawing interest for its architectural qualities, we explore its appeal to the industry as we seek to achieve net-zero targets.

Despite recent volatility within the lumber market, we have recently seen a great uptick in the number of clients choosing mass timber – using engineered wood products as an energy-efficient alternative to steel and concrete – to reach their sustainability goals.

The reason for this is that mass timber creates less waste, leaves a lighter carbon footprint, and can be quicker and cheaper than other traditional construction modes.

According to market research published by MarketsandMarkets™, the global cross-laminated timber (CLT) market is projected to see an annual growth of 14.5 percent, skyrocketing from $1.1bn USD in 2021 to $2.5bn USD by 2027.

The 2021 Mass Timber Report, published by the Forest Business Network, projected an increase in mass timber projects from just below 100 projects in 2018 to nearly 25,000 in 2034.

This is a clear signal that many clients may now be seeing more opportunity in prioritising their net-zero ambitions over potential risks in pricing and low workforce experience.

Updated building code

In January 2021, proposals for tall wood buildings were approved in the 2021 International Building Code (IBC). This now allows mass timber buildings of up to 270 feet (82.2 meters), which equates to roughly 18 stories. This represents a large increase over the previous cap of six stories. This updated policy has had a compounding effect on the number of mass timber buildings planned for construction.

For example, Milwaukee is home to the USA's tallest mass timber building (image above). This 25-story, 493,000-SF mixed-residential building was built in 2021 and is expected to be the first of many tall mass timber buildings across the country.

Lighter carbon footprint

The projected growth of global construction between now and 2060, without any consideration of embodied carbon, is anticipated to add the equivalent of an entire New York City footprint to the world every month for the next 40 years. As it stands today, the built environment generates nearly 50 percent of annual global CO2 emissions.

Although building operations emissions (operational carbon) can be reduced over time through energy upgrades and sourcing renewable energy, the carbon footprint of building materials (embodied carbon) is locked in at construction completion.

As the industry seeks to reduce the impact of embodied carbon, mass timber has increasingly captured the spotlight as a green alternative to traditional steel and concrete.

In comparison to concrete buildings, mass timber produces 30 percent fewer CO2 emissions. That percentage drops to 50 percent fewer emissions when compared to steel buildings. If the industry wants to make an impact, mass timber is a clear solution in North America.

From electrifying existing buildings and transitioning to renewable sources of energy, to experimenting with less traditional construction materials and methods to reduce embodied carbon, there are a growing number of options available to those looking to decarbonise their built assets.

Construction efficiency

We recently undertook a study comparing cost and schedule of mass timber versus steel and concrete for a Seattle office building, concluding that steel costs 11 percent more than mass timber and extends the construction schedule by seven percent.

A cost comparison with concrete was similar (within one percent), but concrete extended the construction schedule by 31 percent over mass timber. A similar study completed by Robert Jackson at Fast+Epp Structural Engineers found similar results.

Like traditional building methods, mass timber’s benefits vary depending on the building design. For example, a mass timber building is more cost effective in large, regularly shaped structures and in situations where fabrication is repetitive.

Therefore, it is far more likely to be, and should be, recommended for projects such as office buildings or apartment blocks where the floor layout is similar throughout.

Adidas campus expansion

The recently completed expansion project at adidas’ North American headquarters achieved an accelerated delivery when the project team conceived a pre-cast concrete and mass timber hybrid structure, which reduced the build schedule by three months.

The timber, locally sourced and manufactured in Oregon, sequesters carbon from the atmosphere and offers an overall smaller carbon footprint than other building materials. It was one of the first of its kind in the USA.

Although there are many benefits, mass timber construction does pose certain limitations. For example, a standard 5-ply CLT floor structure can only span up to 17 feet, which increases the number of columns required.

On the other hand, while increasing the number of columns may result in an increased number of piles, the overall foundation depth may be reduced compared to concrete and steel columns due to mass timber’s lighter weight.

A mass timber future

Mass timber is gaining popularity across North America, encouraged by the advancement of building codes and desire for a more sustainable built environment.

While cost will continue be a driver on many projects, we are already seeing a shift in how the material can play its part to help meet net-zero targets. A local resource without the constraints that using global supply chains brings, mass timber in North America offers many unassailable benefits and should be a key consideration for any up-an-coming building projects, for a more productive and sustainable future.