Traditional Building Portfolio
Period Homes Magazine

 

Opinions

The Case for Structural Engineered Wood


By Jack Merry

The November commentary titled "Common Sense Green Building" by Michael Connor contained a number of inaccurate and misleading statements in support of a specious argument against the performance and environmental credentials of structural engineered-wood products.

Mr. Connor's argument, paraphrased, begins like this: the rise of engineered wood products over the past few decades was devised by "big lumber" as a way to capitalize on low cost "waste-stream products" while deceiving people into believing engineered wood is green by virtue of conserving timber resources. "We are making building materials from waste products and saving trees, so this is a good thing, is it not?" Mr. Connor asks. "Upon closer inspection," he answers, "another perspective emerges, whereby environmentalists are duped and big lumber smiles all the way to the bank."

The argument then jumps from impugning the motives of "big lumber" to challenging the durability and performance of the engineered-wood products they manufacture, particularly oriented strand board (OSB) and wood I-joists. In hyperbolical summary of his argument, Mr. Connor states: "While the actual service life of an I-joist/rafter can be debated until failures are reported, it would be fair to say that if Thomas Jefferson's Monticello had been built using I-joists and I-rafters, visitors today would be viewing an archeological dig, not a museum."

Let's back up a bit. First, structural engineered-wood products are not made from wood waste. OSB, for example, which is commonly used as a structural sheathing for floors, walls and roofs and as the web of wood I-joists, is made from harvested trees, largely from privately managed and certified forests, and often from fast-growing and underutilized species. As a result, old growth and other forests that we have chosen as a society to preserve are more easily safeguarded, and that's one among many reasons those products are rightly considered environmentally friendly.

The other common categories of structural engineered-wood products – wood I-joists, laminated veneer lumber, laminated strand lumber, oriented strand lumber, glued-laminated (glulam) timber, and the original engineered wood, plywood – also make increasingly efficient use of harvested forest resources. None is made of wood waste or the byproducts of other wood manufacturing processes.

The simple fact is that a leading cause of the research and development of more resource-efficient engineered wood products over the past quarter century has been the mandated decline of national forest harvest levels (down approximately 80 percent since the 1980s), not the attempt to refashion new products from wood waste (most of which is used for cogeneration to power manufacturing facilities). The industry has invested billions of dollars in product research and manufacturing facilities in support of this technology transformation.

Mr. Connor also suggests that because engineered-wood products have a shorter history of use than solid sawn lumber, it cannot be claimed empirically that they have as long a service life as solid sawn lumber. That argument could be used against all product innovation, and sounds surprisingly out of touch in this age of heightened public demand for new ways to achieve sustainability and marketplace demand for improved product performance.

In point of fact, the science and technology underpinning the performance and durability of structural engineered-wood products is exhaustive, well documented and accepted throughout the design, construction, standards and building-code communities. The service history of these products in construction applications – approaching 30 years for OSB, for example, and some 75 years for softwood plywood and glulam – has been outstanding. And there is no empirical evidence, or logical compulsion, to suggest that these products will not last as long in service as dimensional lumber or any other structural product.

This should not be surprising. OSB, for example, is manufactured according to the same performance standards as the softwood plywood that Mr. Connor himself uses in the homes he manufactures. There are three basic criteria for qualifying structural wood panel products under these standards – structural adequacy, dimensional stability and glue bond durability. Performance criteria in each of these categories were established by building code requirements and through tests of panel products with known acceptance in the marketplace. The tests evaluate a panel's ability to perform to the expected and necessary level for the intended end use. A partial list of typical tests includes racking, uniform load, concentrated static load, impact resistance, direct fastener withdrawal, lateral fastener strength and linear expansion.

As is well known, structural engineered-wood products actually improve upon many of the inherent structural advantages of wood. Cross-laminated oriented strand board, like plywood, for example, distributes along-the-grain strength of wood in both panel axes. OSB eliminates the negative impacts of knots and knotholes. And wood I-joists and glulam timber can carry greater loads over longer spans than is possible with solid sawn wood of comparable size.

Citing again the shorter history of some of these products in the marketplace, Mr. Connor states that "no empirical evidence exists to prove or disprove…what proper protections are required" to afford durability and long service life. Common sense is rather clear on this point, however – moisture is the enemy of all wood products, and the same protections that routinely apply to dimensional lumber also apply to engineered wood.

OSB, wood I-joists and other structural engineered-wood products have been used for many years now in tens of millions of homes, apartment buildings, office buildings, schools, churches, warehouses and other structures in all kinds of climates around the world. And their performance record is exemplary. We think Jefferson, something of an inventor himself, would have marveled at the ingenuity of these products.

Some of the more spectacular applications of engineered wood technology are the Kibbe Dome at the University of Idaho, which uses laminated veneer lumber to span the school's indoor football arena; the 1.3- million-sq.ft. Park 277 warehouse complex in Auburn, WA, which utilizes a glulam and OSB panelized roof system; the Village at Germantown, TN, a 500,000-sq.ft. senior living facility that incorporates wood I-joists, OSB and laminated-veneer lumber; and the Tacoma, WA, Dome, where a glulam framing system spans 530 ft. (Many other case studies of the use of engineered wood can be found in the publications section of APA – The Engineered Wood Association's website at www.apawood.org.)

We commend Mr. Connor and others like him who champion the preservation of period house designs and materials. They do our society a service. However, given that he has business interests in opposition to products and house designs that compete with those he sells, it strikes us as disingenuous to be characterizing engineered wood as some kind of plot whereby "environmentalists are duped and big lumber smiles all the way to the bank."

Structural engineered-wood products, in short, represent a significant step forward in the design and construction of green, strong, durable, functional and economical structures. And technology advancements are making those products better all the time.  

 


Jack Merry is industry communications director at APA – The Engineered Wood Association, a nonprofit trade association based in Tacoma, WA.

 

 
 

www.traditionalbuildingportfolio.com
Advertising Information | Privacy Policy

Traditional Building Period Homes Traditional Building Portfolio traditional product galleries traditional product reports
rexbilt BuildingPort.com Tradweb Traditional Building Conference Palladio Awards

Copyright 2014. Active Interest Media. All Rights Reserved.