Put aside your visions of rustic log cabins. Wood is experiencing a rebrand. Previously dismissed as a structural material after several major city fires in the late 1800’s led to widespread safety concerns, as well as an economic shift toward concrete and steel, wood is back in the form of mass timber.
The term mass timber encompasses a wide range of products that stack, glue, or nail together layers of soft wood to create large, stable slabs. While ZGF has been designing with these materials for more than 20 years—notably using reclaimed timber from an on-site warehouse at the U.S. General Services Administration’s Federal Center South Building 1202 and salvaging beetle-kill pine for Rocky Mountain Institute’s Innovation Center—mass timber is finally gaining traction. From environmental benefits to technological advancements, mass timber makes the case for a strong future.
The Climate Crisis
Mass timber brings many inherent benefits, but the one that has recently captured the attention of the design and construction industries is its potential to be a part of the solution to address the climate crisis. The key word here is “potential.” An increased demand on one of our key natural resources must be managed responsibly and with future generations in mind. To ensure positive stewardship, ZGF is actively developing sustainable forestry practices and holistic life cycle analysis methodologies (more on that later).
Here’s what we know: buildings are among the largest contributors to the global carbon footprint. Architecture 2030 reports that buildings generate nearly 40% of annual global greenhouse gas emissions with 11% of emissions coming from the embodied carbon associated with building materials alone. Wood is a natural carbon sink, absorbing more carbon as it grows than it releases as carbon dioxide. If harvested responsibly, not only does timber construction avoid the substantial greenhouse gas emissions associated with concrete and steel construction, but timber continues to store CO2 throughout a building’s lifecycle, which can reduce emissions long-term. It is our responsibility as architects to not only design more energy efficient buildings, but to find ways to reduce the embodied carbon footprint of our projects by using low-carbon materials.
Advancement of Building Codes
Mass timber’s many valuable properties have spurred interest in and demand for products. This has resulted in their increased availability and the support of a growing body of research and testing. However, one obstacle has remained: limitations set by the International Building Code (IBC). While heavy timber has long been included in the building code as Type IV construction, building heights and areas were restricted. The introduction of new calculation methods from the National Design Specification for Wood Construction—which allow engineers to determine a project’s precise fire resistance—and recognized standards for testing mass timber products like cross-laminated timber have led to considerable increases in the allowable height and area for mass timber buildings. As a result, the 2021 IBC will allow timber structures to rise to 18 stories. While Europe has embraced mass timber for over two decades and Oregon and Washington have led the charge in the United States—preemptively accepting these changes to the IBC—the sweeping changes to be implemented in 2021 have the potential to help mass timber to catch on nationwide.
Fire and Life Safety
How, exactly, has a material so old been made new again? Let’s begin with safety first. Though mass timber continues to battle the misconception that it would not perform well in the case of a fire or natural disaster, these large, dense masses of wood are a far cry from traditional wood frame construction. Mass timber has been tested and proven to be highly fire-resistant. In the event it does start to burn, it first chars on the outside, forming a protective layer around the interior wood that maintains its overall structural stability.
In the case of earthquakes, mass timber also boasts a high strength-to-weight ratio, making it seismically sound. ZGF is demonstrating this strength on the PAE Living Building, located in the Cascadia Subduction Zone in Oregon. The building is designed to achieve the highest level of seismic resilience—level four—allowing the structure to be habitable following a 9.0 magnitude earthquake.
Comprised of CLT framing and Glulam beams and columns around a concrete core, the PAE Living Building will set a new standard for environmental responsibility and the capabilities of mass timber in the Pacific Northwest.
The Business Case
Though timber currently has a higher material cost than concrete or steel, Think Wood reports that the average mass timber building is 25% faster to construct than a similar concrete building. This speed translates to overall schedule and project cost savings. Prefabricating the building components and assembling them onsite is also safer and faster than traditional construction methods. These efficiencies have been crucial to ZGF’s ongoing work for the Vancouver Affordable Housing Authority (VAHA). The firm is simultaneously delivering four housing projects to VAHA—all under aggressive schedules and located on extremely constrained sites—while navigating the City of Vancouver’s three-year approvals process.
Another component of the business case for mass timber is just beginning to take shape as large corporations realize that there may be fiduciary risk in not taking major steps toward environmental sustainability. In early 2020, Laurence D. Fink, the founder and chief executive of BlackRock, published his highly influential annual letter to the leaders of the world’s largest companies. This year’s letter stated that BlackRock would begin considering environmental sustainability as a core goal in their investment decisions, an unprecedented move that could reshape many corporations’ approaches to sustainable design. So long as it comes from responsibly managed forests, mass timber is no greenwashing; it is backed by evidence proving its substantial impacts. Using this material for the construction of future facilities is a tangible way of mitigating climate change while securing investment capital.
Modular mass timber units prefabricated for four Vancouver Affordable Housing Agency projects have greatly increased construction efficiency.
There’s no denying that wood is aesthetically beautiful, and research has proven that natural materials can enhance occupant wellness and productivity. As we continue to advance biophilic design, mass timber brings the outdoors in, creating a sense of belonging and connecting people to the natural world. In the case of The Rowland Project at Burr and Burton Academy in Manchester, Vermont, an atrium constructed from CLT and Glulam will reflect the surrounding scenic Equinox Highlands area while embracing students in a warm, welcoming atmosphere.
Mass timber is also not an all-or-nothing design choice. Hybrid structural systems that combine timber with concrete or steel can relieve any perceived challenges of mass timber while incorporating its benefits. The firm’s work for VAHA demonstrates that hybrid systems can create an efficient, replicable model for future development. These projects are setting a precedent for new affordable housing stock by leveraging timber, concrete, and steel members for their unique structural performance characteristics.
When viewed as another material in the design toolbox—one that can be modified and adapted to meet the vision and constraints of each individual client and project—even partial use of mass timber can help buildings to become more sustainable, resilient, efficient, and cost-effective.
As ZGF continues to study and test mass timber construction, the firm has recognized that advancement in sustainable forestry and regional economic conditions will be critical to the material’s long-term success as a climate solution. While the potential of mass timber buildings to sequester carbon is exciting, it is essential that we protect our forests to maintain global economic and environmental health. Beyond advocating for the Forest Stewardship Council’s best practices for harvesting, ZGF has been working with Oregon timber mills to research and develop a new process for sustainable criteria and supply chain transparency.
The new method revamps an old technique of segregating logs in the log deck and batch processing them, which allows project teams to track the final product back to the forest of origin. By connecting these dots, ZGF can target landowners whose values align with our clients’ aspirations around responsible natural resource use and climate change mitigation. Recently, the firm has sourced wood from diversified landowners across Oregon to uplift the state’s urban and rural economies, while preserving one of its most precious resources.
It is our hope that telling the local story of the wood in our projects will have a lasting impact in sustainably revitalizing Oregon’s timber industry, effectively differentiating it from timber industries in other regions of the country and overseas. This practice also gives more direct credit to landowners who are managing their lands responsibly, creating another market incentive for sustainable forestry. Transparency is key, because knowing precisely where wood comes from will allow our clients to make informed decisions about the harvesting practices and ecological values they wish to economically support.
Life Cycle Analysis: An Evolving Conversation
Current life cycle analysis methodologies comparing wood to more intensive structural materials, like concrete and steel, show large reductions in embodied carbon. This is especially true if biogenic carbon (the carbon naturally sequestered by trees as they grow) is included in the calculation. Even when considering scenarios in which wood products end up in landfills or incinerators at the end of their useful lives—which would release biogenic carbon back into the atmosphere—wood is shown to be a relatively efficient choice. Current models may even underpredict performance, as more data is needed to fully understand different types of long-lifespan wood products, like structural members and cross-laminated timber.
To elevate current methodologies, ZGF is working with research organizations like Ecotrust to quantify an often-overlooked piece of life cycle analysis: harvest practices. Current life cycle analyses assume that harvest practices are carbon neutral so long as trees are replanted. In reality, this issue is far more nuanced. There are significant differences in the amount of carbon sequestered by a forest that undergoes 40- or 80-year harvest rotation, a plantation engaging in legal-minimum clearcutting, and a small family landowner practicing ecological forestry mimicking natural disturbance patterns. Once we can more effectively quantify these carbon dynamics, we can make better value propositions to our clients about the ecological impacts of our designs.