Timber’s Comeback: Mass Timber as a Sustainable Structural Material

The significance of timber in relation to climate and construction

There are two primary types of emissions that are relevant to buildings: operational emissions (the energy consumed during the occupancy of buildings) and embodied emissions (those generated during the production of materials and the construction of the building). For many years, energy efficiencies and on-site renewable energy sources have been the most accessible solutions; however, embodied carbon is now increasingly acknowledged as the next significant challenge. Numerous life-cycle assessments have demonstrated that mass timber can significantly decrease a building's carbon footprint when compared to traditional concrete or steel frameworks - meta-analyses indicate average reductions in the range of 30 to 40% in cradle-to-grave CO₂e for similar structural systems. This carbon benefit arises from timber's capacity to store biogenic carbon and the reduced energy requirements for processing wood compared to the production of cement or steel.

Beyond emissions, mass timber offers practical construction benefits: CLT (Cross-Laminated Timber) panels are prefabricated to size, which shortens project timelines, reduces on-site waste, and lowers noise and dust - advantages in dense urban retrofit jobs and constrained sites. Furthermore, structural mass timber is comparatively lightweight: research indicates that mass-timber frameworks can significantly reduce structural mass and the use of concrete (one study noted an approximate one-third decrease in weight when compared to similar steel systems), thereby lowering the requirements for foundations and reducing transport-related emissions.

What is CLT (and how does it function)?

Cross-laminated timber is made by layering and adhering pieces of lumber at alternating right angles, resulting in large, rigid panels that perform similarly to concrete slabs or shear walls, yet weigh significantly less. Other forms of mass timber - such as glued-laminated timber (glulam), laminated veneer lumber (LVL), and nail or dowel-laminated timber - broaden the range of structural wood options. The timber industry, academic institutions, and national laboratories have developed handbooks and standards that detail CLT design, fabrication, and detailing for architects and engineers.

Myths regarding performance - particularly those related to strength and fire have consistently posed a significant obstacle. However, mass timber is designed with predictable tolerances: CLT panels exhibit remarkable stiffness and load-bearing capacity, and they char at a slow, quantifiable rate when subjected to fire. This charring offers a level of passive fire resistance, and when paired with gypsum or other protective materials, mass timber assemblies can achieve the standard fire-resistance ratings commonly required in commercial construction. Comprehensive testing and updated product standards (including modifications to CLT product standards and code guidance) have enabled regulators and insurers to build confidence.

Real projects: spanning from Norway to Milwaukee
The most compelling evidence of the feasibility of mass timber is found in built projects. Norway's Mjøstårnet - an 18-story mixed-use tower finalized in 2019 showcased that wood can accommodate hotels, apartments, offices, and public facilities at a significant height while adhering to contemporary performance criteria. The structure utilized glulam and CLT extensively, contributing to a change in perceptions regarding timber in densely populated, cold-climate environments.

North America has experienced rapid growth: The completion of Ascent in Milwaukee, a 25-storey hybrid residential tower made of mass timber in 2022, has pushed the limits of height and has taken advantage of federal testing grants that confirmed the compliance of mass timber assemblies with U.S. codes. Ascent, along with other recent developments, illustrates how hybrid designs featuring a primary structure of timber with specific concrete or steel connections can merge the optimal characteristics of various materials.

Germany has emerged as a frontrunner in the realm of large-scale timber hybrids. The EDGE Suedkreuz in Berlin, which was completed in 2021, stands as the largest freestanding wood-hybrid structure in the country. By using a modular system that combines CLT and glulam with concrete where necessary, it achieves a balance of strength and efficiency. Central to the design is an expansive timber atrium roof that provides over 1,600 m² of communal space beneath a lattice skylight. With a DGNB Platinum rating of 95.4%, this project has established a new standard for sustainable commercial buildings in Europe, showcasing that mass timber can thrive in densely populated urban environments.

In the United States, universities are playing a pivotal role in popularizing timber construction. The University of Pennsylvania’s Amy Gutmann Hall in Philadelphia is set to be the city’s inaugural mass timber building. This six-storey academic hub, encompassing approximately 116,000 square feet, utilizes CLT and glulam to reduce embodied emissions by more than 50% compared to a concrete alternative. In addition to its carbon reduction benefits, the project is a prime example of how institutions can serve as early adopters, advancing codes, supply chains, and public perceptions in areas where timber construction is still emerging.

Additional noteworthy projects include the Wolfson Tree Management Centre at Westonbirt Arboretum in the UK, constructed with timber sourced from the site; the Quinnipiac University Recreation & Wellness Center in Connecticut, a hybrid facility of CLT and steel aiming for LEED Gold certification; and the Weald and Downland Gridshell in Chichester, whose elegant oak lattice has become a lasting symbol of contemporary timber engineering.

Barriers and responsible sourcing
Despite evident benefits, the widespread implementation of mass timber faces significant challenges. Many jurisdictions are slowly updating their building codes and permitting procedures; architects and engineers still require local precedents and proven assemblies to facilitate approvals. Another pressing concern is supply chain capacity: large-scale production of CLT necessitates dependable sawmill feedstock and manufacturing investments, and areas lacking established forestry-to-panel supply chains may experience extended lead times and elevated transport emissions. These limitations raise doubts regarding the most economically and environmentally viable applications of mass timber.

Sustainability depends on forestry practices. Timber retains carbon permanently only when the forest ecosystem is managed in a manner that sustains or enhances overall carbon stocks - merely extracting additional wood from degraded forests or transforming natural forests into plantations can lead to net emissions or a decline in biodiversity. Consequently, responsible certification (such as FSC or PEFC), comprehensive landscape planning, and assurances of regrowth are vital to confirm that mass timber serves as a genuine climate solution rather than a mere manipulation of carbon accounting. (In the context of municipal or corporate procurement, it should be standard practice to specify certified supply chains.

Policies, regulations, and the route to expansion

Policies and regulations are advancing. In North America, updates to building regulations and CLT product standards, supported by extensive fire testing and performance studies, have created opportunities for taller wooden buildings. Public procurement that prioritizes low-embodied-carbon materials, specific incentives for domestic milling capacity, and research and development subsidies for hybrid systems and connections will promote faster adoption. At the same time, life-cycle accounting standards that accurately recognize carbon storage and impose penalties on high-embodied-carbon products will generate market demand for timber.

Looking forward: hybrid designs and circular timber

The near future of mass timber is characterized by a combination of mixed and modular approaches: hybrid systems that utilize timber in its strongest applications and concrete or steel where necessary (such as in cores and foundations) serve as effective pathways to wider acceptance. Prefabricated timber modules offer advantages in terms of speed, quality assurance, and reduced waste - all of which align with the objectives of circular construction. Additionally, research focused on the deconstruction and material recovery of CLT panels will be essential; designing for disassembly transforms the recyclability of timber from a theoretical benefit into a practical circular strategy.

Conclusion

Mass timber may not be a cure-all, yet it serves as a significant tool in the decarbonization toolkit. When obtained sustainably, engineered timber stores carbon, minimizes embodied emissions, and offers practical construction benefits that address contemporary urban issues. The technical data and existing projects are already reassuring regulators, developers, and designers - however, to fully realize timber's comeback, it will need coordinated policies, responsible forestry practices, increased manufacturing capabilities, and ongoing research into fire safety, acoustics, and long-term durability. Should these elements align, future skylines could once again feature wood - this time, purposefully integrated as part of the climate solution.

REFERENCES

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Source: Structural Timber Association