First developed in Austria and Germany in the 1990’s, cross-laminated lumber has increased in popularity and usage over recent years. Although new to North American residential and non-residential construction, it has shaped a new class of wood and timber called “massive timber” (Bradford, 2012).
Cross-laminated lumber, more commonly referred to as CLT, is a kind of wood paneling used in wood fabrication as well as construction that is offered as a new and unique alternative to conventional building materials such as concrete, steel, brick or normal, chemically-treated lumber.
With a steadily rising increase in usage of cross-laminated timber in the United States, workers such as architects, researchers, interior designers and engineers are drawn to this emerging technology and its advantages as compared to older building methods and materials.
This paper seeks to provide the reader with a broad overview of information on the history, design, fabrication, usage and impact, advantages and challenges of cross-laminated timber.
In order to meet the need for an alternative wood-based product in North American construction and building, cross-laminated timber was designed and manufactured in order to better serve contractors, architects and engineers in their respective projects (Bradford, 2012.
). Made up of 3 or more layers of 2-by-4 beams placed at a 90-degree angle (or “crosswise”) then glued together, CLT cross-sections can be formed in many different, alternating configurations, with the option of a double-layer being possible (hence the “cross” portion of the lumber’s name). As a man-made, engineered wood product, CLT thickness ranges from .
75 to 2.5 inches (Schmidt).
Essentially, this type of wood gives a “sandwiched” look when finished. Similar to other load-bearing buildings, CLT provides support through it’s design. Starting at a wider base, cross-laminated lumber begins to thin and taper towards the top as the load becomes lighter. This design allows CLT to take up less floor space as well as decrease the need for dividing columns in repeated structural walls (Schmidt).
As cross-laminated timber was further developed and utilized, producers were able to pinpoint some key advantages in its usability. Because it is much lighter in weight compared to other building materials such as steel or concrete, cross-laminated timber is also much less energy-intensive. Due to it’s light-weight feel, CLT is much easier to handle, transport, and operate with. With this ease of handling, this lumber can also be assembled on-site much faster than that of it’s normal, chemically treated lumber counterpart.
With the grain within each layer sitting at a right angle to the slate of wood above and below it, CLT creates counter-tension in the panels that allows this type of lumber to be used for building extremely tall structures (phys.org). In addition to it’s low density and ease of implementation in building, cross-laminated timber can also be composed of more “visually blemished” panels of wood that would otherwise go to waste, thus maximizing materials during a project (Bradford, 2012).
As a result of it’s sound engineering, cross-laminated timber and wood panels provide consumers with high-quality performance in terms of acoustic, seismic, fire and thermal ability. According to the BDC Network, the fabrication of cross-laminated timber creates such a lightweight product that it virtually “put’s itself out” if caught on fire, acting more like a concrete than wood product, as well as maintaining a “significant structural capacity” for exposure to extremely hot or fire-prone areas for long periods of time (Spickler, 2014).
Furthermore, CLT also possesses a flexibility that has little impact on the environment, adding to it’s ever-growing list of advantages and overall appeal (CLT). Not only can CLT be used for the building of very large structures, it can also be implemented in commercial or non-residential construction. Due to it’s diverse nature, cross-laminated timber is both cost-competitive and a factor in increased economic growth.
After it’s addition into the International Building Code (IBC), CLT has become a more viable solution for cheaper lumber alternatives. Supplemented with cheaper (up to 50%) installation costs, CLT’s ease of handling can also contribute to projects being completed at a much faster rate.
As well as this increased rate of completion, it can also significantly decrease the occurrence of injuries as well as foundation costs due to it’s weight. Although CLT should not be a substitute to light-framed construction, it does offer a more eco-friendly and cost-competitive/effective supplement. In an online article written by Gillian Flaccus and Phuong Le from Phys.org, cross-laminated timber can contribute largely to current and future economic growth. Not only can CLT potentially reduce a carbon footprint of a more “urban” city due to lower level of greenhouse gas emissions, it can also provide consumers with a renewable building material option (Flaccus, 2016).
To elaborate more on the eco-friendliness of cross-laminated timber, we can also analyze the process in which it is actually fabricated or manufactured. In North America (both Canada and the United Stated), CLT are made of spruce or other timber with a smaller diameter. Because of the size of the actual trees being used to create CLT, energy efficiency increases while overall jobsite waste is essentially terminated (Bradford, 2012).
With it’s superior qualities and innovative design in comparison with other, older wood-based building materials, cross-laminated lumber usage continues to increase over time. Although it can be used independently in construction, as knowledge on this material begins to grow, contractors and architects have begun to use CLT to create “hybrid” structures and buildings.
Moreover, though primarily comprised up of softwood, especially in America, producers are in the early stages of creating hardwood cross-laminated timber (Cole, 2018). In addition to cross-laminated lumber, different products such as Glulam and Laminated Veneer Lumber (LV) have also entered the market, seeking to mimic entry into the lumber market as other alternatives to the usual masonry materials, although CLT shows a more promising future (Gintoff, 2016). Despite these advances, however, some challenges still pose a threat to the continual use of CLT in the present-day.
Albeit the increasing interest on the subject of cross-laminated timber utilization in construction, there are still some potential problems present with it’s implementation. As a result of it’s fairly recent entry in to the North American market, CLT has had little to no extensive research done on it’s overall structural soundness. Although CLT provides excellent load-bearing for tall structures, building codes in the United States have limited height to a maximum of 6 stories, with anything reaching above 85 feet requiring further review, testing or approval (Cole, 2018). Considering its short history, CLT is currently being produced in limited quantities in North American and Europe so it’s performance can be examined more extensively, making sure it can live up to certain standards before it is mass produced (Schmidt).
Since CLT is engineered, as previously stated, it requires extensive approval and code acceptance, which poses a new challenge to this product’s future. Despite being introduced into IBC code laws, CLT is still required to pass certain safety tests than can produce results displaying it holds up to the same safety standards and performance as other wood-based materials, concrete or steel used in construction. Even though limited records show a positive correlation between cross-laminated timber and fire or seismic performance, research is still constrained to the last two to three decades, whereas other building materials have a long history of records that can be trusted.
Since it’s development in Europe in the 1990’s, cross-laminated timber, or CLT for short, has since made its way into Northern American construction practices. Known for it’s eco-friendliness, lightweight feel, diversity, and load-bearing ability, CLT shows a promising future in the addition to everyday building materials.
Though it poses a few major challenges, cross-laminated timber has been becoming a more integral part of the lives of architects, contractors, researchers, and builders alike. Used as an alternative to materials such as steel and concrete, CLT offers a new and innovative way to look at wood fabrication and can contribute largely to sustainability in the future.
Over the years, as advances in the world of wood fabrication take place, it is often commonplace to utilize the newest, most exciting products in everyday work, however, it is crucial that all materials used in the forming and building of structures be thoroughly reviewed and coded accordingly in order to ensure worker safety as well as the safety of the consumers.