Engineered wood products such as cross-laminated timber have been getting a lot of attention lately.
Architect Michael Green’s Wood Innovation Design Centre (WIDC) in Prince George, British Columbia, is a six-storey building made entirely of engineered wood. Green has proposed wooden buildings up to 30 storeys.
In contrast to Green, architect Roald Gundersen takes a different approach to building with wood. Rather than chipping trees and re-forming the pieces with adhesive, Gundersen’s company, Whole Trees Architecture and Structures, has developed methods for using whole peeled logs for columns and trusses.
Using government grants and private investment, Gundersen’s team has performed research at the US Forest Products Laboratory to test Y-branched trees under axial loads and to test the parallel-chord trusses that join with the Y-branched trees. They then determined the design specifications of whole trees and branched columns, and designed patent-pending steel connectors that tie the parts together.
Logs are delivered to the company’s production facility where they are stripped of bark, treated to make them insect- and fire-resistant, and graded for strength. Then his crew builds the trusses as specified, from six to 17 metres long.
Gundersen said that when properly engineered, whole trees can effectively replace steel and concrete components. From a strength-to-weight perspective, wood is nearly as strong as steel in compression, and is twice as strong in tension. Compared to milled lumber, whole-tree timber can support 50 per cent more weight than the largest piece milled from that tree. Milling trees into lumber, Gundersen said, removes the concentric, continuous, and spiraling fibres that developed during the tree’s growth and allowed it to accommodate wind shear without tipping over.
One of the company’s current projects is a 5,300 square metre grocery store in Madison, Wisconsin. The building will use 295 parallel-chord trusses built from red pine trees from southwest Wisconsin, and 34 support columns made from 45 centimetre diameter ash trees harvested from the city of Madison due to the emerald ash borer.
Gundersen’s objective is to produce columns and trusses at commercial scale and at competitive cost, replacing steel and concrete components with more environmentally sustainable wood components. According to a report published by researchers at the Yale School of Forestry and Environmental Studies, titled Carbon, Fossil Fuel, and Biodiversity Mitigation With Wood and Forests, replacing all concrete, steel, and brick used in building with wood products would lessen global greenhouse gas emissions by 14 to 31 per cent, and lessen fossil-fuel consumption by 12 to 19 per cent. The researchers say the carbon reduction comes mostly from avoided emissions, with less coming from the wood actually sequestering carbon in a building or forest.
Globally, production of concrete accounts for about five per cent of CO2 emissions, and obtaining the raw materials requires large-scale mining operations. Brick-making produces 0.63 kilograms of carbon per brick, on average, and the kiln firing also produces substantial air pollution. Steel-making contributes about three per cent of global CO2 emissions.
In addition, the whole tree approach makes use of materials that can be useful for building but might otherwise be wasted. Ash is a strong and fast-growing hardwood tree, so it can be useful for projects such as Gundersen’s. Millions of ash trees in cities throughout the eastern and midwestern US will be removed and replaced due to the spread of the emerald ash borer (EAB). The EAB, a transplant from China discovered in Michigan in 2002, is 100 per cent fatal to American ash trees, which have no natural defense. Pesticides are available but require periodic use and are costly, so many municipalities have opted for removal and replacement, creating a ready supply of material. Rather than chipping or burning the trees and releasing their carbon, they can be used for building.
Similarly, forests in western North America have been ravaged by the mountain pine beetle. The beetle has killed millions of acres of pine trees that now harbor standing dead trees, which creates a substantial fire hazard. The trees remain a useful material for building for several years, though both drying and rotting in place limit their usefulness over time. In addition to projects like Gundersen’s, these trees are suitable for use in engineered wood products such as glulams and cross-laminated timber.