Wood, one of the oldest building materials, has been continuously reinvented throughout history. As contemporary architecture becomes more and more concerned with sustainability and environmental responsibility, the popularity of the material has also increased. As trees absorb carbon dioxide during their growth, their wood stores that carbon, keeping it out of the atmosphere. The materials derived from wood are thus associated with less greenhouse gas emissions on the condition of trees being harvested from sustainably managed forests. But in order to capture the full potential of this material, a plethora of techniques and modifications have evolved with the purpose of adapting and customizing wood’s characteristics to the demands of modern design and construction. From thermal modification to engineered wood or versatile particle boards, these methods not only enhance wood’s suitability for the rigors of contemporary architecture but also expand the usability of this sustainable material to an unprecedented scale.
Engineered Wood: Laminating and Gluing
Engineered wood is a large category describing construction materials created by binding together layers of particles of wood using adhesives and advanced manufacturing processes. The processes are used to optimize the strength, stability, and dimensional consistency of the material while also enabling the creation of large structural elements out of trees with relatively small sections. Some of the most common types of laminated panels, also commonly referred to as ‘mass timber,’ are Glued Laminated Timber (Glulam), Cross Laminated Timber (CLT), and Laminated veneer lumber (LVL).
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The structural qualities of these materials depend on the manufacturing process. Glulam is created by bonding individual segments of wood with industrial adhesives. As the fibers of the wood are oriented in the same direction, this type of wood is best used for large-sized structural elements such as beams or columns. On the other hand, CLT consists of planks of sawn and glued wood, with each layer oriented perpendicular to the previous one. This creates structural stiffness in both directions, similar to plywood, but with thicker components. CLT panels can function as structural walls, floors, furniture, ceilings, and roofs, with their thickness and dimensions adapted during the prefabrication phase. LVL is built by combining thin layers of veneer with the grain running in the same direction, with uses similar to Glulam, but featuring a higher performance and allowing for smaller cross sections compared to softwood glulam.
Read more: The Meteoric Rise of Cross-Laminated Timber Construction: 50 Projects that Use Engineered-Wood Architecture
Pressure and Heat Treatments
Thermal modification is a wood treatment process involving exposure to high temperatures in kilns, reducing moisture content to nearly 0%. This eliminates bonding water and free water within wood cells, which reduces deformations and stabilizes the wood. Steam is then applied, bringing humidity to 4-7%, making it viable. Thermally Modified Timber (TMT) is more stable and moisture resistant compared to untreated wood, reducing the risk of cracking and warping while maintaining its natural appearance.
Pressure treatments are used to force wood preservatives or fire retardants into the internal structure of the wood. This can prolong the timber’s longevity by safeguarding it against wood-eating insects and fungal decay. Additionally, fire retardant treatments also increase the versatility of wood by minimizing the smoke and flames produced during a fire. The applications expand from interior framing to wood exposed to outside conditions, including utility poles, railroad ties, deck boards and fence pickets.
Read more: How Thermal Modification Can Make Wood in Architecture Last a Lifetime
Aggregating Wood Particles
Wood particle boards are one of the most versatile and widely used construction materials, often used as wall coverings, furniture, ceilings, and even flooring. To obtain them, wood fibers, particles, or fragments are bonded together with adhesives and resins, resulting in robust panels with various properties depending on the type of aggregates and adhesives.
Oriented Strand Board (OSB) is known for its strength and cost-effectiveness. While OSB panels are most commonly used as sheathing as one of the many invisible layers of a building, many designers have also explored their potential in interior design. Medium-Density Fiberboard (MDF) features smooth surfaces, becoming a preferred material for carpentry, while Medium-Density Particleboard (MDP) uses wood debris such as sawdust mixed with resin, offering a lower-cost solution. Plywood boards are processed similarly to CLT, but at a different scale, created by overlapping wood sheets glued perpendicularly and heat pressed.
Read more: Wooden Boards: Differences Between MDF, MDP, Plywood, and OSB
Surface Treatments
There are numerous surface treatments that can be applied to wood to enhance its appearance, durability, and protection. Some common types of surface treatments for wood include painting, staining, varnishing, lacquering, and oil and wax finishes. While some of these rely on modern materials, vernacular and traditional techniques also sought to prolong the longevity of wood. One such technique is the Japanese craft of carbonizing wood. The method, now over three hundred years old, involves burning the outer layer of the wood, creating a layer of charred material that protects the inner structure from termites, fungi, and other natural elements.
Read more: Carbonized Wood: A Traditional Japanese Technique That Has Conquered the World
Bending
Most wooden structures and applications of wood in architecture employ wood shaped into straight elements such as beams and flat panels. Wood, however, has its own elasticity, a property that can be explored and heightened through various techniques. Steam bending is one of the first ones used, as exemplified by German carpenter Michael Thonet who pioneered the method at the beginning of the 1800s, creating furniture designs that continue to be popular to this day. Glued Laminated Wood also allows for shape modifications by gluing pieces following a mold of the desired curvature while respecting the material restrictions of the type of wood used. This opens the possibility of creating larger pieces fit for architectural use. The Kerf Cut method, on the other hand, gives more flexibility but also weakens the structural qualities of the resulting element.
Read more: How to Bend Wood
Post-Tensioning
Post-tensioning, a form of prestressing, is a technique most commonly used for concrete structures to improve their structural performance and allow for thinner elements. When talking about wood, post-tensioning integrates structural elements made of engineered timber, like beams, walls, or columns, with steel bars or tendons. The steel elements are affixed to the timber components and are then tensioned using hydraulic jacks, introducing a force within the timber element to counterbalance the expected external loads. The resulting elements feature increased seismic resilience in addition to the added structural efficiency.
Read more: Learn About Seismic Design of Wooden Buildings With These Online Resources
Editor’s Note: This article was originally published on September 21, 2023, as part of the ArchDaily Topics: The Future of Wood in Architecture presented by Tantimber ThermoWood.
Tantimber ThermoWood brings the timeless warmth of wood to modern design. Natural, renewable, and non-toxic, they transform sustainably sourced wood species into dimensionally stable and durable wood products for use in residential and commercial building and design projects. Find out more about how the enduring beauty of ThermoWood brings warmth to the built environment.
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