Mass timber — engineered structural components made by joining smaller pieces of wood — is emerging as an alternative to steel and concrete for larger buildings. Lighter and less energy-intensive to produce, it can reduce emissions associated with construction while storing carbon. Researchers are also exploring its potential benefits for human health and well-being.
But building with wood isn’t automatically sustainable. Mass timber’s sustainable potential depends on how forests are managed, how the material is manufactured, and whether its components can be reused at the end of a building’s life.
In this Q&A, Alan Organschi, Professor in the Practice and Director of the Building Lab at Yale School of Architecture, explains the promise of mass timber—and what it will take to realize it. The interview was edited and condensed for clarity.
What is mass timber and how does it differ from conventional wood building materials?
Alan Organschi: Mass timber is the mechanical or chemical adhesive lamination of smaller pieces of wood to produce very large engineered structural members. It uses laminated boards to produce large beams and columns, or cross-laminated panels used for floors, walls, and roofs.
Unlike light-frame construction, mass timber can be used for larger projects and to build more densely. Due to revisions of the International Building Code, we can now build from the ground up to 18 stories using mass timber, whereas light-frame construction is typically limited to five stories.
What types of buildings are best suited to mass timber?
Organschi: Most of the buildings we construct in cities to meet the needs of housing and to create dense, convivial urban spaces are somewhere between five and 12 stories. That’s the sweet spot for mass timber.
At around eight stories, for example, it may be one of the most efficient materials for creating dense, multistory housing. You can’t build that high economically with light-frame construction, while steel and concrete really start to make more economic sense at greater heights.
So if you want to build dense, mid-rise housing—and store carbon in the process—mass timber is a particularly strong option.
What are the key environmental benefits of using mass timber in construction?
Organschi: Mass timber can have lower greenhouse gas emissions across a building’s life cycle than materials like steel and concrete. It doesn’t require the high heat used to produce cement or smelt iron, and because it’s lighter, it takes less energy to transport and requires smaller equipment on the construction site.
Mass-timber components are also largely prefabricated, so they can be assembled more quickly on site. And because wood is a low-density material, it’s naturally insulating and doesn’t conduct heat energy through the building envelope the way steel or concrete can.
Together, those benefits can reduce emissions associated with producing, transporting, and building with the material.
Are there health and well-being benefits to building with mass timber?
Organschi: There’s a growing body of research on the benefits of exposure to natural materials and nature, from the visual and psychological benefits of biophilic design to measurable physiological effects. Studies of wood-lined classrooms, for example, have found reduced heart rates and lower cortisol levels among children.
Wood also has physical properties that may support healthier indoor environments. It is hygroscopic, meaning it absorbs and releases moisture in response to changes in the surrounding air. That can help buffer indoor humidity and reduce moisture swings, potentially supplementing mechanical systems in some buildings.
We’re still beginning to understand many of these relationships, but the potential benefits of organic materials can extend from the biochemical to the planetary.
You describe mass timber as a ‘potentially sustainable’ building material. Can you explain?
Organschi: Simply substituting wood for steel or concrete isn’t enough. If we don’t address the necessary safeguards at the source or the potential for reuse at the end of a building’s life, we could turn this technology into just one more extractive industry—in which wood becomes a flimsy alibi for ecological predation.
To realize its potential, we need to look at the whole system: how forests are managed and harvested, what materials are used to manufacture mass timber, and what happens to it at the end of its life. The larger goal should be regenerative: using demand for wood not just to reduce carbon emissions, but potentially to incentivize ecosystem health and help restore forests.
What would it take to scale up mass timber without putting greater pressure on forests?
Organschi: The scale is significant, and there’s no single approach. One tool, for example, is forest farming. Yale graduate Mark Wishnie and his team in Brazil have been planting eucalyptus forests for the paper industry while allowing successive forest growth to transform into more indigenous forests. They’ve shown that it can increase habitat and draw down carbon.
But we also have to understand where we harvest, which forests need to be protected, and how to balance competing demands for land. At the same time, we need a more robust circular economy that reuses the huge amount of material already embedded in our buildings and cities, rather than relying entirely on new resources. And we have to rethink how we build cities, controlling sprawl and making better use of existing building stock.
What are the biggest obstacles to wider adoption of mass timber?
Organschi: We’re still in a very early adoption phase. There’s a lot of conflicting or poorly understood information about issues like fire risk, pests, and deforestation, as well as a longstanding cultural bias that sees wood as a provisional material rather than something as strong and durable as concrete.
The building industry is also still learning how to work with these materials, particularly the highly prefabricated components and specialized construction methods involved. And there are broader systemic barriers, including policy, finance, manufacturing capacity, and the relationships among forests, manufacturers, and the architecture, engineering, and construction community.
Those barriers are starting to smooth out, but wider adoption will require changes across the entire system by which we produce buildings.
What Yale is doing with mass timber:
Yale is increasingly incorporating mass timber into building projects as part of its efforts to lower the carbon intensity of construction. At 37 Hillhouse Avenue, a cross-laminated timber (CLT) addition to the historic Graves-Gilman House uses CLT for bearing walls, floors, roofs, and an egress stair.
Five different mass timber products were used as structural components at Yale Divinity School’s Living Village, which is expected to be certified as the largest living building on a university campus. The structure is built with super-insulated mass timber assemblies, including glue-laminated columns and beams and cross-laminated timber floors, and most of the wood products were locally sourced and are Forest Stewardship Council-certified.
Mass timber was also used in the renovation of the Yale Peabody Museum, notably in the new Central Gallery, where the Archelon and Tylosaurus fossil specimens are suspended from glue-laminated mass timber beams.
At Osborn Memorial Laboratories, Yale is using a hybrid structural system that combines glue-laminated timber columns with CLT and concrete floor slabs. The approach demonstrates how mass timber can be integrated with conventional materials to meet the specific structural and performance requirements of a building.
Yale’s Building Lab is also exploring how mass timber can contribute to a circular economy. In 2023, students and faculty used CLT floor panels salvaged from USDA fire-safety tests and wall components made from manufacturing offcuts to prefabricate the structural assembly of the Horse Island Coastal Research Station for the Peabody Museum.