WOOD, A VIRTUOUS MATERIAL
Innovative processes, allied with natural sustainability and durability, could push a wood renaissance.
Wood is strong, lightweight, easy to modify into a wide variety of forms, and has innumerable uses in construction.
The American Wood Council (AWC) claims it is used in over 90 percent of residential construction, according to information on its website (www.awc.org). Recent innovations in wood products and a focus on this material’s benefits are increasing its use in non-residential construction.
Wood is a surprisingly green product. According to the Consortium for Research on Renewable Industrial Materials (CORRIM), it takes less energy to manufacture wood products than steel or concrete. The AWC says, "Wood is the perfect green building material because it is renewable, stores carbon that reduces greenhouse gases, and is energy efficient."
The use of wood as a building material has some significant obstacles. According to the AWC, for example, rating systems such as LEED carry anti-wood bias. Nevertheless, a recent report from the U.S. Forest Service found that using wood in building products yielded fewer greenhouse gases than other common building materials, such as concrete and steel, making it the greenest construction material.
Innovations in wood products and a number of cutting-edge projects have continued to advance the use of perhaps the most versatile building material available.
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Green trees are green
Woodworks, an initiative of the Wood Products Council, and a cooperative venture of all the major wood associations in North America, research organizations and government agencies, provides resources that allow engineers, architects, general contractors, developers, and others to build non-residential structures out of wood more easily and at less cost. Lisa Podesto, P.E., senior technical director, says Woodworks is a "one-stop-shop in wood construction."
Woodworks, an initiative of the Wood Products Council, and a cooperative venture of all the major wood associations in North America, research organizations and government agencies, provides resources that allow engineers, architects, general contractors, developers, and others to build non-residential structures out of wood more easily and at less cost. Lisa Podesto, P.E., senior technical director, says Woodworks is a "one-stop-shop in wood construction."
"The sustainability aspect of wood is really beginning to set in with people. People thought for a long time, ‘Oh we’re cutting down a tree, this can’t be a sustainable project’ but now they’re realizing this isn’t the case," Podesto said.
Unlike steel or concrete, wood regenerates itself. Wood-based products have drastically increased the speed of construction, along with providing superior characteristics such as moisture retardation, fire resistance, advanced performance in seismic situations, and long building life.
It’s wood, but it’s better…
Innovative wood products and systems have evolved by huge leaps and bounds. Pre-fabrication techniques and engineered wood products such as Glulam, SCL, Wood-I joists, trusses, and cross-laminated timber have created new opportunities for the old material.
Innovative wood products and systems have evolved by huge leaps and bounds. Pre-fabrication techniques and engineered wood products such as Glulam, SCL, Wood-I joists, trusses, and cross-laminated timber have created new opportunities for the old material.
Light-framed wood construction, common in residential design, is perhaps the most standard use of wood for structural construction. Framing of this sort is commonly used on buildings up to six-stories high.
Heavy timber frame and cross laminated timber (CLT) products have applications up to 10 stories. CLT is made from crosswise glued layers of wood boards (of low, medium, or high grade) with an average thickness of 20 to 38 millimeters. The cross lamination of the wood minimizes swelling and shrinkage and increases resistance. CLT panels are used for floor, wall and roof systems. Often pre-assembled wall sections are lifted into place with cranes and attached to each other with long screws or steel brackets. This method of construction offers major time-saving benefits when compared with concrete or steel.
"Cross-laminated timber changes the dynamic/scope of what a wood-building is," Podesto said. "Heights can be much higher, two-way slabs of CLT act like a concrete slab vertically/horizontally. They have excellent seismic performance. The connections are simple and streamlined. For every reason cross-laminated timber is a new realm for the wood industry."
Panelized roofs, made out of both all wood and hybrid materials, are being used primarily in the West Coast. These flat and low-slope roofs are fabricated on the ground and lifted into place with cranes. "It is absolutely genius how fast these go up," Podesto says.
Fire resistance
Although wood is more "combustible" than concrete or steel, recent studies have proved that in many ways a wood structure can be far safer in a fire than structures built with other materials.
Although wood is more "combustible" than concrete or steel, recent studies have proved that in many ways a wood structure can be far safer in a fire than structures built with other materials.
Canadian Sustainable Timber (CST) Innovations claims that the low surface area of this product doesn’t sustain a flame, so fires burn themselves out, according to information in its website (www.cstinnovations.ca). Additionally, "Airtight construction lowers the fires’ oxygen supply, gas does not travel through the panel" and "heat does not conduct from one side of the panel to the other," according to CST Innovations.
Heavy timber also resists fires through charring, which acts as an insulator by preserving the inner wood and allowing beams to maintain their strength during a fire.
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| The Earth System Science Building — UBC in Vancouver, British Columbia, an example of construction using some of the latest technologies in sustainability and comprised of cross laminated timber. Photo by John Boys, Structurlam |
Seismic performance
A number of studies have been performed on the seismic performance of wood-framed structures through "shake testing" – building models placed on a shaking platform.
A number of studies have been performed on the seismic performance of wood-framed structures through "shake testing" – building models placed on a shaking platform.
Woodworks details a number of characteristics that allow wood-frame buildings to perform well in earthquakes.
1) More connections provide redundant load paths for earthquake forces. If one connection becomes overloaded, its load is shared with those surrounding it.
2) A high strength-to-weight ratio. Wood buildings are typically lighter than their steel or concrete counterparts, an advantage in an earthquake.
3) Flexibility. Connections in a wood-frame system have some flexibility, allowing for absorption and dissipation of energy.
4) Resistance to lateral forces. Engineered wood-frame buildings and structural panels like plywood or OSB, in combination with studs and joists, create shearwalls that resist the lateral forces experienced during a seismic event.
Thermal benefits
Woodworks cites a study conducted by CORRIM that exudes the thermal qualities of wood. "According to the report, the homes framed in steel and concrete would require 17 and 16 percent more energy, respectively (from extraction through maintenance), than their wood-framed counterparts," the study says.
Woodworks cites a study conducted by CORRIM that exudes the thermal qualities of wood. "According to the report, the homes framed in steel and concrete would require 17 and 16 percent more energy, respectively (from extraction through maintenance), than their wood-framed counterparts," the study says.
Wood also has 400 times better insulating properties than steel and 15 times better insulating properties than concrete. Woodworks attributes this to the cellular structure of wood, which contains air pockets, where the solid composition of concrete and steel facilitate heat loss and therefore are less energy efficient.
As a case-study example, the Austria House, nestled just north of Whistler Village, in British Columbia, is said to be so well insulated that it doesn’t even need a furnace. The house is made almost entirely of wood.
"Indeed, where nearly every Canadian builder installs sheets of gypsum drywall, Sohm Holzbautechnik mounted solid walls of spruce two-by-fours. The boards are stood vertically, and lined up one after another, so that only a two-inch side is visible. All of these boards are held together using patented diagonal wooden dowels, which eliminate the need for toxic glues or chemicals of any kind," Monte Paulson wrote in a Jan. 26, 2011, article published in TheTyee.ca.
The Austria House is a good example of a "Passivhaus" or Passive House, one designed to use significantly less energy. Thick, well-insulated walls decrease heat and energy transfer from the inside to the outside. The Austria House is constructed with a series of layers, nearly every one made of wood.
The future
Podesto feels that wood can do many of the same things in structural construction that steel and concrete can do, and often better.
Podesto feels that wood can do many of the same things in structural construction that steel and concrete can do, and often better.
"The problem is: it’s new… It always takes a few years for code to catch up with innovation and, once that happens, people are going to feel more comfortable and see that there’s a lot of potential there," she said.
A big hurdle is being able to teach people about the systems and code aspects of wood.
Podesto, who is not the only critic of the current code, feels that current building codes are not written with the wood industry in mind.
"Much of the code aspects can be overcome with alternate means, but current regulations kind of pigeon-hole wood as a stick-frame, and there’s all these other uses of wood out there," she said.
Christina M. Zweig is a writer at ZweigWhite. She can be contacted at christinaz@zweigwhite.com.
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