Trees – logs – mass timbers.
It seems so natural but in the totality of construction, mass timbers are still being discovered by many builders and developers.
The Centre for Interactive Research on Sustainability, at the University of British Columbia, showing off some timber
If you’ve ever been inside a mass timber structure, you know the unique look and feel it gives to buildings. While many countries around the world have been using it for as long as anyone can remember, the US is still lagging behind in adopting it as a standard building material.
Mass timber refers to a category of framing styles typically characterized by the use of large solid wood panels for wall, floor, and roof construction. They also include innovative products such as Cross-Laminated Timber (CLT), Glulam (glue-laminated timber), and Nail-Laminated Timber (NLT), among others.
While not considered a true mass timber, another timber product that has recently hit the market, the T-Stud, is defined in this article.
Timber is a renewable resource, and sustainably managed forests can serve as a carbon sink. Using wood in construction stores carbon, whereas producing steel or concrete emits carbon. This makes timber construction a more environmentally friendly option.
Mass timber panels can be prefabricated, leading to faster construction times compared to conventional methods and many people find the look of exposed wood aesthetically pleasing, which can be an advantage for certain commercial applications looking to achieve a specific design feel.
Modern engineered timber products can be as strong as traditional building materials, but with the added benefit of being lighter and contrary to popular belief, large solid timber components can perform well in fires because they char on the outside, which can protect the inner core of the timber and maintain structural integrity for a period of time.
Mass timber buildings can be designed to be flexible and dissipative, which may offer advantages in earthquake-prone areas. Timber is generally lighter than steel or concrete, which can lead to savings in foundation costs and transportation. It also has natural insulating properties that can contribute to energy efficiency in buildings.
However, there are a few things that tend to hold back its acceptance.
Many people associate wood with fire risks and may not be aware of the advancements in mass timber construction. This can be a barrier to its wider adoption.
In regions where mass timber is a newer building method, it might be more expensive than traditional construction materials due to lack of supply chains, expertise, or demand.
Without proper treatment or maintenance, timber can be susceptible to pests such as termites and can be susceptible to mold and rot if it’s exposed to prolonged moisture.
Mass timber requires sustainably managed forests to be truly environmentally friendly.
Not all contractors or construction professionals are familiar with mass timber construction techniques, leading to a potential knowledge gap. Building codes in many regions are still catching up with mass timber. In some areas, there might be restrictions on the height of wooden buildings or other limitations.
In summary, while mass timber offers numerous advantages, particularly concerning environmental impact and aesthetics, it’s essential to weigh these against the potential drawbacks and local conditions when considering it for commercial construction.
Cross-Laminated Timber
Cross-Laminated Timber (CLT) is a type of engineered wood product. It consists of multiple layers of solid-sawn lumber, each layer oriented perpendicular to the adjacent layer and then glued together to form a thick, solid wood panel.
Lumber used for CLT is typically softwood, like spruce, pine, or fir, although other species can be used. The lumber is planed and dried before use. The boards are laid down side by side to form a layer. Subsequent layers are laid with their boards at a right angle to the layer below.
Then the layers are bonded together using adhesives. The type of adhesive varies but is typically one that’s durable and resistant to environmental degradation. After gluing they are layered and pressed together to ensure a solid bond. This can be done using hydraulic or vacuum presses.
Once the adhesive has set, the large CLT panel can be cut to size, and openings for windows, doors, and other building elements can be created.
One of the primary uses for CLT is as structural wall panels. They can be used in both exterior and interior walls and can be used for floor and roof systems, providing a solid base.
In multi-story buildings, CLT can be used for core elements like stairwells and elevator shafts. Some buildings use CLT as the primary structural system for the entire building.
CLT panels can be manufactured to precise dimensions, allowing for rapid assembly on site. This prefabrication can lead to reduced construction times and due to its cross-laminated structure, CLT has strength in both directions (along and across the grain).
Environmental: Wood is renewable, and using it in construction sequesters carbon. Additionally, the production of CLT can be more energy-efficient than the production of concrete or steel.
CLT can be used in various architectural styles and can be combined with other construction materials.
While wood is combustible, the mass of CLT panels means they char on the outside when exposed to fire. This char layer can protect the internal structure of the panel and provide a degree of fire resistance.
CLT has gained significant attention in the construction industry, especially in the context of sustainable and efficient building practices.
Glulam (glue-laminated timber)
Glulam, or glue-laminated timber, is an engineered wood product made by gluing together individual layers or laminations of dimensional lumber. The grain of all laminations runs parallel with the length of the member, distinguishing it from other engineered wood products like Cross-Laminated Timber (CLT).
The lumber, often softwood, is seasoned (dried), then planed to ensure smoothness and accuracy in thickness. Then each layer (lamination) is coated with a durable, moisture-resistant adhesive. The coated laminations are stacked and then placed into a press, which applies pressure until the adhesive cures.
After curing, the glulam can be cut or shaped, often to precise specifications, including curved shapes that are not typically achievable with solid timber.
Glulam is commonly used for long-span heavy beams and columns in both residential and commercial structures. They can span large distances without the need for intermediate supports.
One of the unique advantages of glulam is its ability to be manufactured in curved shapes. This feature is used in arches, curved beams, and other architectural details. Glulam is also utilized in bridge systems due to its strength and versatility.
Large open spaces, such as gymnasiums or pools, often use glulam for its aesthetic appeal and its ability to span wide areas.
Glulam can be produced in a wide range of shapes, sizes, and configurations, making it suitable for a vast range of applications and can be stronger than steel by weight. By strategically placing higher-grade laminations where stresses are highest (usually the outermost top and bottom portions of a beam), glulam can be optimized for structural performance.
Glulams can offer a warm, natural aesthetic that many people find appealing, especially when left exposed in a structure.
Wood is renewable, and glulam often makes use of smaller pieces of lumber that might be waste in other circumstances. Like other wood products, it sequesters carbon.
While wood is combustible, a Glulam charred layer can protect the internal structure of the member and provide some fire resistance.
Some builders or designers who are not familiar with glulam might perceive it as a specialty product requiring unique expertise, which could be a barrier to its adoption.
Overall, glulam offers an efficient, versatile, and aesthetically pleasing wood-based solution for many structural and architectural challenges.
Nail-Laminated Timber (NLT)
Nail-Laminated Timber (NLT) is an engineered wood product created by stacking dimensioned lumber (typically 2x4s, 2x6s, 2x8s, etc.) on edge and nailing them together. This straightforward assembly creates a solid wood panel. The name comes from the process itself: the individual lumber pieces are laminated together using nails.
The chosen lumber, often softwood but not exclusively, is arranged in a desired orientation with the boards stacked side by side, typically on edge.
Then the stacked boards are fastened together using nails. Sometimes screws or other mechanical fasteners can be used, but nails are traditional.
NLT is commonly used for floor and roof systems in buildings but can also serve as wall panels, both for structural and aesthetic purposes.
The production and assembly of NLT panels are relatively straightforward, which can make it a favorable choice for projects with a tighter budget or timeline. Like other mass timber products, NLT offers a warm, natural wood appearance that can be left exposed in the finished construction.
While NLT doesn’t provide the same level of versatility in shapes like glulam, it still offers considerable flexibility in terms of size and application. NLT panels can be effective in reducing sound transfer and vibration in buildings.
While NLT, like other mass timber products, can char and protect its core from fire to some extent, fire protection measures might be needed, especially in certain types of buildings or jurisdictions.
NLT is a part of the growing family of mass timber products that are increasingly seen as viable, sustainable, and aesthetically pleasing alternatives to traditional construction materials.
T-Stud lumber
The T-Stud is a relatively new type of building product aimed at improving the thermal performance and structural capabilities of traditional framing lumber. It’s essentially a modified stud that seeks to minimize thermal bridging (the flow of heat across the more conductive components of the building envelope) while maintaining or even enhancing structural strength.
A typical T-Stud consists of two lumber members connected by an internal truss system, often made of dowels or other small wood components. The space between the two lumber members is either left empty (providing an air gap) or filled with insulating material.
T-Studs are primarily used as a replacement for traditional 2x6s or 2x4s in wall framing. By doing so, builders can achieve walls with better thermal performance without significantly changing the traditional framing method.
While their primary application is in wall systems, there’s potential for T-Studs to be used in other framing scenarios where both structural strength and thermal performance are concerns.
The main advantage of T-Studs is the reduction of thermal bridging. By minimizing the amount of solid wood that spans from the interior to the exterior of a wall, the transfer of heat is reduced. The insulative properties can be further improved if the gap between the two lumber members is filled with insulating material.
Despite the reduced amount of solid wood, the internal truss system can provide significant structural strength, making T-Studs suitable for load-bearing applications. T-Studs are designed to be compatible with typical construction methods, meaning that builders don’t need to learn a whole new system to use them.
As a specialized product, T-Studs might have a higher upfront cost compared to traditional lumber and being relatively new and specialized, T-Studs might not be as widely available as traditional lumber products.
As with any new building product, there might be a learning curve or resistance from builders who are unfamiliar with it or who haven’t yet seen its benefits firsthand.
In summary, T-Stud lumber is an innovative approach to improve the energy efficiency and structural performance of wood-framed buildings. As energy codes become more stringent and as the industry places a greater emphasis on green building and energy conservation, products like the T-Stud could see increased adoption.
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Gary Fleisher, the Modcoach, author
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