United States Secretary of Agriculture Tom Vilsack Tuesday announced a US$1 million program to be implemented by the US Department of Agriculture (USDA) Forest Service in partnership with the Wood Products Council’s WoodWorks initiative, according to a USDA press release this week. The initiative will provide training for architects, engineers and builders related to the use of advanced wood materials in US buildings.
The program supports both The President’s Climate Action Plan goal of preserving the role of forests in mitigating climate change and the objective of the recently-signed 2014 Farm Bill to create rural jobs.
In its own release also Tuesday, the Softwood Lumber Board (SLB), a division of the Softwood Lumber Council, said it applauds the USDA announcement on the benefits of using wood in taller buildings at its workshop “Building with Wood: Jobs and the Environment” hosted by the White House Rural Council.
Across the US, wood product businesses support more than 1 million jobs and provide billions in economic growth in rural communities, says SLB. The benefits of using wood obtained through sustainable forestry practices include green building, a smaller carbon footprint and creation of jobs, often in rural areas. A recent lifecycle analysis found that harvesting, transporting, manufacturing, and using wood for structural and appearance products yields fewer air emissions–including greenhouse gases–than the resource extraction, manufacture, and use of other common building materials.
Cross Laminated Timber
The Binational Softwood Lumber Council, a non-profit organization, was established in 2006 by the Canadian and US Governments. The Council is leading the effort to increase the use of wood products as part of the shift to green building.
According to Wood for Good, an organization that advocates for sustainable wood construction, a ton of bricks requires four times the amount of energy to produce than a ton of sawn softwood; concrete requires five times, steel 24 times, and aluminum 126 times. Wood also performs better. It provides, for example, five times more insulation than concrete, and 350 times more than steel.
“The market for wood and other forest products currently supports more than 1 million direct jobs, many in rural America,” said Jennifer Cover, PE, Executive Director of WoodWorks in the USDA press release.
Recent architectural trends in sustainable urban densification have spurred a movement toward increasingly tall buildings made from mass timber products or a combination of wood and other materials, says a February 26 Wood Works report. Many tall timber building concepts are motivated by their suggested advantages in sustainability resulting from the use of wood as a renewable resource and low carbon construction material.
The simple beauty of mass wood, or cross-laminated timber (CLT) is its orthotropic quality. Normal wood is strong in the direction of the grain but weak in the cross direction. CLT’s perpendicular layers make it strong in two directions. And because it relies on layers of smaller beams, it can reduce waste by using odd-shaped, knotty timber that lumber mills would otherwise reject.
Two recently constructed land mark buildings in Melbourne are using CLT, says a March 16 report by ABC News in Australia. An uptake in its use could prove a timely boost to Australia’s timber industry.
The two big projects discussed, Victoria Harbour in Melbourne’s Docklands, the world’s tallest timber residential building, and Lend Lease’s nearby A£$20 million Docklands Library and Community Centre, use CLT panels made of European Spruce, a type of softwood. Each is 16 metres long by three metres high, fit readily into a shipping container and simply need giant screws to fit them together on-site.
Elsewhere, Swedish authorities have approved a 34-story wood tower in Stockholm, while Michael Green, a Vancouver, BC, architect, is seeking approval for a 30-story tower in his city. And the Chicago architecture mega-firm Skidmore, Owings & Merrill recently published a feasibility study for a 42-story tower made predominantly of CLT.
Anatomy Of A Timber Tower
(first published in the March 2014 issue of the Popular Science journal)
- Whereas steel or concrete structures are skeletal, using columns to carry loads, CLT towers distribute weight over the entire, solid vertical panel.
- Steel or concrete L-brackets fix the horizontal and vertical CLT panels together.
- The horizontal spans between vertical CLT elements can be significantly longer than with steel or concrete beams.
- Interior walls are usually fireproofed by applying a layer of gypsum paneling on top of the mass timber panels.
- A two-inch layer of concrete typically covers two two-inch layers of insulation (separated by a three-inch void) to reduce acoustic vibration between floors.
- Panels come made to order with windows cut out and sometimes piping and electrical installed. Construction is as easy as screwing the panels together.
- Elevators have double walls with insulation sandwiched between them for fire safety and soundproofing.
It has become a competition among architects to see who can build the next tallest wood high-rise, says Frank Lam, a professor of wood building design and construction at the University of British Columbia.
It took just 27 days for four men, working three days a week, to erect the timber portion of a nine story CLT building which now sits in East London called Stadthaus, which is about 30 per cent faster than a comparable steel-and-concrete structure. Instead of building the tower from scratch on-site, it was more like assembling a piece of furniture.
It is estimated that the wood in Stadthaus stores 186 tons of carbon while the steel and concrete for a similar, conventionally built tower would have generated 137 tons of carbon dioxide during production.
Demographers predict that the planet’s urban citizenry will double in 36 years, increasing the demand for ever-taller structures in ever-denser cities. Whether architects and construction firms build those towers from unsustainable materials like steel and concrete or employ new materials like CLT could make a huge difference in the Earth’s health. Put differently, the world’s urban future may just lie in its oldest building material.
Due to technological advances of CLT production and the requisite changes to building codes as mass timber constructions continue to pass, and surpass, building code requirements, there is a growing number of wood buildings in the 5 – 10-story range globally. As well, CLT is helping to overcome longstanding challenges (area/size/fire regulations) in the 1-4 story segment.
A recent report prepared by FP Innovations suggests that US residential and non-residential construction in the 5-10 story range represents a volume potential of up to 4.6 billion board feet (roughly 75 per cent of the market in the US greater than 4 stories is in the 5-10 story range).
There are now 16 modern tall wood buildings that have been built around the world over the past five years, according to the Softwood Lumber Board website. That trend appears to be accelerating. The promotion of tall wood construction in North America is gaining momentum with the recent publication of a tall wood building research report by Skidmore, Owings & Merrill (SOM) funded by the Softwood Lumber Board.
In January, JAS on CLT was officially recognized in Japan. Now the Japan CLT Association has been formed, by three manufacturers, according to Japan Lumber Reports. The next step to incorporating CLT building in Japan is the setting up of standard strength and design methods for Japan Building Standards Act. The CLT Association is actively recruiting members in advance of these new building codes in order to expand and develop CLT building, and has a growing list of applicants says the Reports.