The Oregon Zoo in Portland, home to the World Forestry Center, expects to install that state’s first building using cross laminated timber (CLT) this month, according to the Portland Tribune Thursday. As well, US home builder DR Johnson is reportedly building one of America’s first CLT production facilities in Riddle, OR.
Cross Laminated Timber
Madison’s regular readers are familiar with Structurlam, a successful CLT manufacturer in Okanagan Falls, BC.
CLT is an engineered wood product made of 2-by-6s glued together in huge sheets then cross-hatched in three to nine layers, that can be used to erect highrises up to 40 stories. It can be up to 18 inches thick, 10 feet wide, and 80 feet long. If this “plywood on steroids” supplants concrete and steel in larger buildings, it could lower carbon emissions and construction costs while creating new jobs in rural forestry communities.
CLT also can be made from lower-grade timber, especially the layers that won’t be visible.
Oregon’s timber industry is subject to wild swings due to it’s dependence on the cyclical homebuilding industry, explained Thomas Maness, dean of the College of Forestry at Oregon State University to the Tribune, so finding new uses in commercial buildings could help weather future downturns and create more job stability.
In terms of construction, it takes at least a dozen workers to install reinforced concrete, he says, but only four or five to frame with CLT. Because crews are working with large components custom-made in the plant, CLT buildings can go up much faster — about a floor per week vs. 2.5 weeks for concrete.
A new study was conducted by Mahlum Architects and Coughlin Porter Lundeen Engineering, both out of Washington State, and Walsh Construction of Seattle, WA, to determine the feasibility of CLT construction in the Pacific Northwest, mainly focusing on Seattle. The first of it’s kind, the study found that CLT construction is cheaper than conventional methods, but not by much. However, the study predicts that in the future, building material could get a lot cheaper, according to the Journal of Commerce October 8. It also reduces the carbon footprint of buildings.
Tall Wood Structures
That study defined “low high-rise buildings” as being taller than 75 feet but shorter than 125 feet. When compared to the base 10-storey concrete building, the CLT option offered an estimated four per cent cost saving.
As for the carbon footprint, in Britain — where the construction industry accounts for almost 7 per cent of the economy (including 10 per cent of total employment) — 47 per cent of greenhouse gas emissions are generated from buildings, while 10 per cent of CO2 emissions come from construction materials, said The Guardian October 8. Furthermore, 20 per cent of the materials used on the average building site end up being discarded as residue.
British Columbia allowed six-storey residential wood buildings five years ago, which resulted in more than 50 structures being built and another 250 in planning stages. Ontario also recently altered its building code to allow for six-storey wood residential structures.
The University of British Columbia in Vancouver, BC, issued an Express Of Interest this summer for architectural firms to design a wood-based high-rise tower between 16 to 18 storeys. At a height of 53 metres, it will be the world’s tallest wooden building of its kind. The mixed-use student housing wooden tower will include new academic space, up to 400 beds for upper year and graduate students, and student amenities – all in a floor area of 157,000 square feet.
In 2011 the eight-storey Bridgport House went up in London, UK, in 10 weeks.
A 10-storey CLT tower, Forté, opened in Melbourne, Australia, last year, and Danish architect CF Moller has won a building competition with designs for a 34-storey residential wooden skyscraper in Stockholm, Sweden.
In Europe, a 14-storey wooden building is currently under construction in Bergen, Norway, with another eight-storey structure on its way up in Dornbirn, Austria – the prototype for a 20-storey ‘plyscraper’ (plywood skyscraper) designed by the global engineering firm Arup.
Arup is currently working to educate engineers in China on the use of wood.
“Timber, despite being the world’s oldest construction material, is now the most modern,” said Alex de Rijke, director of London-based dRMM architects, to the Financial Times September 26. “It has undergone a renaissance in terms of processing and manufacturing of engineered timber, as opposed to just building with joists and planks. It’s now a whole family of very sophisticated, high-performance engineered products. CLT is the ‘new concrete’.”
Protection from the elements is key, explained Liam Dewar, director of Eurban, timber engineers and contractors to Financial Times. He said CLT has “a lifespan equivalent to concrete or masonry”, and points to old churches in Britain and Europe that have timber beams which have been around for hundreds of years.
A Yale University-led study published in March estimates that “the world’s forests contain about 385 billion cubic metres of wood, with an additional 17 billion cubic metres growing each year. A mere 3.4 billion cubic metres is harvested annually, mostly for subsistence fuel burning; the rest rots, burns in fires, or adds to forests’ density,” writes 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 carbon dioxide emissions, fossil fuel consumption and represent a renewable resource. Managed properly, this can be done without loss of biodiversity or carbon storage capacity.”
CLT has been slow to gain a foothold in the United States, which many blame on antiquated building codes that limit wood buildings to five or six stories. But new building codes should end those height limits, and that likely will get adopted by Oregon next year.
This year the Singapore Civil Defence Force (SCDF) officially revised its fire code after a thorough safety assessment to allow the use of CLT for structural components in buildings, according to EcoBusiness September 16. This change came about thanks to the efforts of Australia’s Lend Lease, which has been leading efforts to promote the use of CLT technology in Singapore as a cost-saving, environmentally-sustainable building system.
Singapore’s government has been cutting back on foreign manpower quotas to soothe the growing friction between locals and foreigners in the densely-populated city. The price of sand has also jumped as several Southeast Asia countries have banned the export of sand and granite to Singapore, citing environmental degradation caused by sand extraction.
Initially Singapore stipulated that CLT buildings could not exceed four storeys. Eventually, the height limit for CLT buildings was increased last November to a maximum of 24 metres, or six or seven storeys, after authorities conducted a further European study tour of CLT buildings.