MASS TIMBER IS DAWNING ON THE TEXAS MARKET AS A VIABLE ALTERNATIVE TO REINFORCED CONCRETE AND STEEL CONSTRUCTION. HERE, TWO TEXAS ARCHITECTS DISCUSS THEIR EXPERIENCES WORKING WITH THE MATERIAL.
A subcategory of engineered wood, mass timber refers to a range of products made by bonding small pieces of wood together to form larger structural sections that can rival the strength of steel and reinforced concrete. The system uses smaller trees efficiently and sustainably to produce a material that is more durable, longer lasting, and more fire-resistant than standard dimensional lumber. While mass timber’s popularity — specifically, that of glued laminated timber (glulam) in combination with cross-laminated timber (CLT) — has been growing in Europe as well as in the northwestern United States and Canada for more than a decade, it is only in the last few years that the southeastern U.S. has begun to see buildings incorporating this material.
Texas’ introduction to CLT came about when a handful of composite structures incorporated mass timber with steel and concrete. Austin’s 901 East 6th Street, by Thoughtbarn and Delineate Studio, was one of these, as was The Soto in San Antonio, a podium mass timber building by Lake|Flato. According to the nonprofit WoodWorks — which educates designers, engineers, and construction experts and offers technical support for wood building design free of charge — there are currently more than 1,000 mass timber projects across the U.S. Sixty-nine of those are now underway in Texas.
Over the past two years, our firm, Kirksey Architecture, has had an opportunity to design two full mass timber projects, both of them for Houston-area college campuses: San Jacinto College’s new 122,000-sf, three-story classroom building, and the Rice University Hanszen College dorm addition. Since mass timber is so new to the region, we faced a learning curve and had to do a fair amount of due diligence to use the material optimally. What follows is a synthesis of our research and lessons learned from the classroom building.
Aesthetics
Perhaps the most compelling reason to use mass timber has to do with wood’s time-honored visual and sensual appeal. Biologist Edward O. Wilson coined the term “biophilia” in 1984 and defined it as “the innate tendency to focus on life and lifelike processes.” Research suggests that this connection became biologically encoded in humans as we evolved and is critical to our physical and psychological comfort: For building occupants, mass timber yields distinct though subliminal biophilic benefits.
A study at the University of British Columbia found that the presence of wood in a room helps reduce stress, boost productivity, and improve concentration. It compared wood’s stress-reducing properties to a walk in nature. The structure of a building can create a space in which people want to work, live, and play.
When one thinks of a mass timber building, the image that comes to mind is exposed wood. In our projects, we want building users to see a pure wood ceiling, uninterrupted by mechanical and lighting systems, and a virtual forest of columns marching throughout the space. We also want to illuminate the material with daylight, so that people can experience the wood’s natural grain. Expressing the structure reveals its simple construction and provides occupants with a warm, no-frills environment far away from the coldness of concrete and the industrial connotations of steel.
Achieving this appearance can be challenging. The things you don’t see become as important as the things you do see. What would be the least visually disruptive pathway for utilities, for instance? Structural bay design helps us examine the possibilities. A one-way structural solution can easily create a path between girders, while a two-way structural solution might consider under-floor air distribution.
Mass timber components are held together by way of traditional steel connections, and designers must decide how much to express or conceal these essential details. The results can be a delicate and elegant surprise or a bulky and clumsy letdown. At San Jacinto College, celebrating wood is at the heart of the building’s concept, but it is a refined and simple celebration that gives the structure an unassuming character. Each mass timber component, whether it be wood columns or steel connections, is designed to be part of a larger showcase expressing the authenticity of the materials.
Sustainability
There are numerous environmental benefits to using mass timber. It reduces deforestation by relying on carefully managed forests and requires less energy to manufacture than do most contemporary structural systems. It also sequesters significant amounts of carbon for the life of the building and produces fewer carbon emissions during production. According to Architecture 2030, the embodied carbon of building structures is responsible for 11 percent of global greenhouse gas (GHG) emissions and 28 percent of global building sector emissions per year. As architects, we need to provide solutions that reduce these numbers.
In an initial study for San Jacinto College’s classroom building, our project team compared embodied carbon between mass timber and reinforced concrete. The results showed that a reinforced concrete structural design would generate six times more GHG or carbon emissions than mass timber. This is not surprising. Chatham House, a London-based think tank and policy institute, states that more than four billion tons of cement are produced each year, accounting for around 8 percent of global CO2 emissions. While sustainable innovations such as plastic-reinforced concrete and carbon-fiber-reinforced concrete exist, they still need to prove their durability and reliability compared to mass timber.
Structural steel is also a large contributor to GHG emissions. According to the International Energy Agency, the iron and steel industry is responsible for 7 percent of global CO2 emissions, and some estimates place it above 10 percent. While steel’s high recycled content does reduce the material’s embodied carbon by a factor of five, its production still creates a high level of emissions that could be avoided through reusing existing structures or designing with lower carbon intensity materials like mass timber.
Durability
Wood materials for structural components, especially those we can feel and touch every day, can seem less durable to owners than painted sheetrock or CMU block. However, mass timber can be remarkably durable as both structure and finish. Understanding how to treat the surface of the wood is an important part of learning about mass timber characteristics.
Protecting the mass timber structure is essential: Sun can fade the wood, and snow and rain can discolor it. Base sealers applied to the wood at the factory provide protection during transportation and against UV rays and fading. Different sealers applied in the field can vary the end result, so requesting samples of the particular species of wood used in the project is vital to ensure that the sealer does not yellow the wood or turn the surface too glossy. The type of building and the way its parts are intended to be used will determine which sealer is best. For example, in an educational building, it is important to plan for additional coats to protect the material from heavy foot traffic in the corridors, as opposed to inside the classrooms.
Working with other trades, transportation, and erection are all factors that can result in damage to the mass timber components, but dents and scratches can be sanded down and, in severe instances, individual members can be replaced post-installation.
Financial Benefits
Mass timber can significantly reduce project costs. Wood has traditionally been a steadily priced commodity, offering significant savings over steel. Less time is required to erect mass timber frames, primarily because steel erection must be thought of in two parts: erection and detailing. While the erection time may be consistent project to project, the detail time can vary greatly. In steel construction, a builder may have two large cranes and a truck-mounted crane and be able to erect the steel frame and decking within three weeks. However, an additional six or more weeks may be required to detail the steel. During this time, the subcontracting crews cannot begin the process of hanging ductwork or laying out conduit runs.
With mass timber, there is typically only one large crane on site. The erection crew is smaller, and overall movement is slower. However, as soon as the ground-level wood frame and deck are installed, subcontractor crews can start the installation process for pipe hangers, duct straps, and other MEP components. Since the material is the finished product and no extra detailing is necessary, other than sanding off marks from transportation and erection and sealing, other trades can begin work. This alone can result in significant savings in a project. There is no waiting for concrete supports to be removed or welding of steel components to be completed.
Since wood is lighter than steel or concrete, foundations for mass timber buildings do not have to be as robust. In fact, regarding the projects we have been involved with, and in our discussions with other firms across the country, foundation cost reductions appear to run in the 10–30 percent range when compared to conventional steel or concrete frame buildings. Reductions generally come from smaller point loads for columns, lesser foundations for lateral systems, and a myriad of other project-specific conditions in below-slab pad preparations.
The success of a new mass timber market in the southeastern United States can be greatly affected by the development of new manufacturing facilities that can work with southern yellow pine (SYP). We anticipate that building owners will see future cost savings associated with these new facilities because of their location near the source of the fiber. This is a primary factor in mass timber becoming a cost-competitive product when compared to steel and concrete. New manufacturing facilities could create opportunities for private landowners, giving them options to sell timber. Furthermore, SYP as a market commodity has historically cost less than such traditional mass timber wood species as spruce, fir, or pine. Lastly, the shorter distance from factory to job site in the southeastern U.S. will speed up delivery, resulting in further price reductions while also lessening the carbon footprint. New CLT manufacturing facilities have recently opened in Alabama, Arkansas, and Texas, but more manufacturing is needed. For Texas markets, SYP is becoming readily available, which will ideally lead to more competitive pricing. The new student housing project at Rice’s Hanszen College will be made up of SYP components from a newly opened facility in Conway, Arkansas.
Achieving a cost-effective mass timber structure also requires establishing a structural grid that uses the least amount of material possible. There are many potential solutions, so analyzing different configurations of columns, beams, and deck thicknesses is important. According to Ethan Martin of DCI Engineers: “Optimization studies explore several grid layouts adjusting deck thickness, which affects beam sizes. As glulam is a highly priced component in mass timber, reviewing the best ratio of purlins to deck thickness needs an expert eye.” Ultimately, these studies can help reduce the amount of material needed, saving tens of thousands of dollars.
Cost evaluations should also consider prefabricated connection types and the role of wood for lateral bracing in a building. The complexity and variety of solutions for prefabricated connections should be planned carefully. Slot, or dovetail, connections are quicker to install. Although more expensive, they may reduce the amount of time a crane is needed on site compared to the standard saddle or slotted connections. While using CLT panels would be possible for shafts and lateral bracing, steel or CMU would be more compatible with current building codes and allows for a more flexible design.
Another cost-saving measure is to use the manufacturer’s standard sizes. A manufacturer’s machinery requirements often determine the standard dimensions, and exceeding them can lead to material waste and extra cost in transportation.
Coordination
Understanding the construction process and the sequence in which materials come together is invaluable when designing a mass timber building. As in any project, coordination is critical, but it starts earlier on a mass timber project; otherwise, efforts to bring warmth and elegance to the exposed deck can go awry. In a building with exposed concrete or steel structure, the industrial feel may be acceptable and even desired, but the same should not be the standard for mass timber.
During conceptual design, it is important to set the intent of revealing the wood and then figure out where utilities will run. As the design advances, mechanical, electrical, plumbing, and fire suppression should undergo extensive coordination via building information modeling (BIM). One example of extensive coordination is trying to conceal the sprinkler system. It is vital to work with a subcontractor during the BIM process to plan beam penetrations so they can be made in the shop, as it is difficult to justify the time it takes to do so on site.
The prefabrication of penetrations can save valuable time in construction, but it is important to keep in mind the erection tolerance for each structural element. Almost all buildings sit on concrete foundations that set the stage for the construction tolerances of the superstructure. The fabrication of mass timber is extremely precise — typically within a margin of about 1/16 of an inch — but when these elements are erected on site, it is necessary to consider the tolerances of dissimilar materials, such as steel and concrete construction. Some fabricators will not charge for penetrations made during the CNC process, which saves hundreds of hours of manual labor creating penetrations through masses of wood. Still, in areas where there is no construction tolerance, it may become necessary to cut beams or decks on site.
With any new type of construction, stepping outside the box can be daunting. At San Jacinto College, throughout the design process, we explored a variety of ideas about how to express the lobby’s mass timber structure. It was important that the design not be ornamental, but rather stay true to its structural needs. One of the most appealing ideas involved glulam columns that curved to form the roof beams, resembling a barrel-vaulted ceiling. Glulam is far more flexible in its design properties than most people assume, but to bring such a feature to fruition, a team needs to be united in directing the material to its strengths. Ultimately, as the options were evaluated based on cost and speed of construction, it was determined that we could not be assured that erection of the curved members would go according to schedule, so the solution turned out not to be right for this project.
Conclusion
At first glance, designing with mass timber may appear simple and straightforward, but the process exposes unseen complexity that is necessary to achieve the best results and truly celebrate the material’s natural beauty. For architecture firms embarking on a new journey to design a mass timber project, research and communication with the engineering team and construction professionals are crucial. Developing and committing to a highly collaborative partnership can’t just be a marketing slogan on your company’s website. The success of a mass timber project is the direct result of ownership buy-in. Without a client’s commitment, a hundred different reasons will appear out of the blue to lure you away from achieving the goal.
As Texas takes on more of these projects and our industry becomes familiar with the lessons learned by experienced design teams, a more efficient and predictable marketplace will be established. Along with providing a biophilic presence, mass timber will ultimately prove to be faster to install, inherently fire protected, and more sustainable. It is difficult not to “root” for its continued growth.
Michelle Giuseppetti-Old, AIA, and Melika Mirzakhani, AIA, are senior associates at Kirksey in Houston.