The Good Wood—Timber and Engineering Wood
Tetra Tech’s High Performance Buildings Group is considering how timber—our most ancient building material—is undergoing a modern makeover and is now helping us meet the challenges of sustainable, contemporary construction.
As the building industry grapples with unprecedented global challenges—hyper-urbanization, dwindling resources, and climate change among them—timber and engineered wood products are emerging as sustainable solutions.
Project teams are embracing timber as an environmentally sustainable and renewable material, and using it to build faster, cheaper, and more sustainably than ever before. So how can new systems’ approaches to timber create new opportunities, accelerate construction times, reduce costs, and create stronger value chains?
Cross laminated timber (CLT), hailed as the new concrete by some, has become popular overseas as it is lightweight, durable, and easy to assemble. Large panels of timber, sometimes called jumbo ply, are glued and pressed together. They are then cut to size off-site, reducing build time and costs with it. Aside from being around 30 percent lighter than traditional structures, buildings made with CLT also require less energy to heat and cool.
Lend Lease has used the material on two projects in Melbourne’s Docklands—the 10-story residential tower, Forté, currently the world’s tallest timber apartment building, and the Library at the Dock, the first public building in Australia to achieve a 6 Star Green Star rating. At the Library, the lightweight nature of CLT reduced the requirements for new foundations, enabling the building to be constructed just 8 meters (26 feet) from the water’s edge. The result is a building that is both spectacular and sustainable.
Forté’s 759 CLT panels of European spruce turned up on site like flat packed furniture, weighing around 485 tonnes (535 tons). By using timber instead of concrete or steel, the building has eliminated around 1,450 tonnes (1,600 tons) of of carbon dioxide (CO₂), the equivalent of removing 345 cars from the road for a year. The building’s energy efficient design is also saving residents around AUD$300 (USD$200) a year each on their power bills.
Manufactured from smaller, fast-growing trees and sustainably harvested, engineered wood products aren’t reliant on large pieces of solid timber, meaning it is a quickly renewed material. What’s more, waste chip is able to be recycled for further use. The manufacturing processes for engineered wood products in general require a moisture content of less than 15 percent, resulting in a finished product that is more stable and less prone to shrinkage. The end product is also free from the flaws generally found in timber, so the consistency in quality is preferable and generates even less waste.
Laminated veneer lumber (LVL) is another high-strength engineered timber product manufactured by assembling wood veneers with a waterproof bond. The process maximizes the strength of the wood, with the veneering process eliminating any imperfections in the grain. As a result, LVL is uniform and comparable in strength to solid timber, concrete, or steel. It can also be more durable and less prone to shrinking or warping. It is relatively low cost and can be manufactured to any length or shape.
One good example of LVL in action is found in Spain at the Metropol Parasol in Seville. Completed in 2011, the building spans more than 11,000 square meters (36,000 square feet) and reaches 28 meters (92 feet) tall, making it one of the world’s largest timber buildings. The complex includes an archaeological museum, a farmers’ market, bars and restaurants, and a raised plaza, as well as eye-catching wooden parasols—all made from waffle-like wood panels with a polyurethane coating.
Another benefit of timber is that it can be harvested locally, with sources renewed and unwanted material recycled. And of course, timber’s carbon storage potential is impressive. Australia’s native forests, timber plantations, and wood products are net absorbers of greenhouse gases, sequestering an estimated 56.6 million tonnes (62.4 million tons) of CO₂ a year, and reducing our greenhouse gas emissions profile by almost 10 percent.
But do we grow enough timber to meet demand? A Yale University-led study published in March 2014 estimated that the world’s forests contain about 385 billion cubic meters (13.6 trillion cubic feet) of wood, with an additional 17 billion cubic meters (600 billion cubic feet) growing each year.
“A mere 3.4 billion cubic meters [120 billion cubic feet] is harvested [annually], mostly for subsistence fuel burning; the rest rots, burns in fires, or adds to forests’ density,” says Professor Chad Oliver, director of the Global Institute of Sustainable Forestry at Yale University in the Journal of Sustainable Forestry.
“Swapping steel, concrete, or brick for wood and specially engineered wood equivalents would drastically cut global CO₂ emissions, fossil fuel consumption, and represent a renewable resource. Managed properly, this can be done without loss of biodiversity or carbon storage capacity,” Professor Oliver adds.
Another challenge for the mass-timber industry is the way its use is regulated in Australia. Currently, under the National Construction Code, timber systems are restricted to three stories with taller buildings, such as Forté, requiring an alternative solution design. Forest and Wood Products Australia has prepared and submitted a proposal for change to the Australian Building Codes Board to create a voluntary deemed-to-satisfy solution, which would allow timber construction up to 25 meters (82 feet) in height.
While the beauty of wood is timeless, engineered wood products are emerging as an industry game changer—one that may enhance the productivity of our industry and secure the future of the planet.
Tony Arnel, Global Director, Sustainability