Image Source: MaineSci (www.umaine.edu)
Wood I-joist with LVL flanges
and OSB web material
Engineered Wood Products
New developments in engineered wood products have led to materials that are more versatile, resource efficient, and capable of spanning longer dimensions. These engineered materials lack defects, inconsistencies, and other stresses commonly seen in solid sawn lumber.
Weyerhaeuser TrusJoistTM has several engineered wood products currently available to the residential construction industry. Timberstrand Laminated Strand Lumber (LSL) is used for wall systems, beams, and headers. It has the appearance of OSB (although all the strands are typically positioned in the same direction, OSB strand orientation is mismatched for panel strength) but the LSL dimensions are the same as sawn studs and headers. LSL provides the ability to design and construct walls up to 30 feet in height without twisting and shrinking concerns.
As the text box below discusses, the overall use of engineered wood products in the homebuilding industry has increased rapidly in recent years. While part of this growth is due to product development and process improvements, the example of LVL also highlights that the pathway from innovative materials to a market-accepted product can take many years and is also influenced by external factors such as the price of competing products and shifts in resource supplies.
Market Growth of an Innovative Material
Engineered Wood Products: Over the past decade, the use of engineered wood products in the U.S. has grown at a rapid pace of roughly 250 million board feet per year. Several factors have led to the increased market growth, including higher prices for sawn-lumber products and changes in resource characteristics. Engineered products were relatively expensive in the past, but the rise in sawn lumber costs as well as the increase in competition within the engineered wood manufacturing sector has helped to decrease the gap between lumber and wood products prices. Tree harvesting practices have also influenced the emergence of engineered wood products. Harvesting practices have moved towards shorter rotation and the use of faster-growing, lower quality tree species. Engineered wood products offer the industry an opportunity to add value to smaller, lower structural quality logs.
One such engineered product, Laminated Veneer Lumber (LVL), has been a popular choice in construction as an alternative to large solid-wood or steel beams, girders, headers, and I-joists. LVL is generally manufactured using a process comparable to that for plywood, except for differences in wood grain orientation and the roll press process. The parallel grain orientation used to manufacture LVL allows the product to carry large loads over increased spans.
LVL, which was first used for airplane propellers in World War II, was initially developed as a building material in the late 1960's. LVL began to make an impact on the wood products industry in the late 1980's and early 1990's, due mainly to a shift towards composite materials within the industry. This shift was due in part to the greater resource utilization possible with engineered wood products and their ability to utilize fast growing, small diameter trees. As a result, the use of products such as LVL and wood I-joists increased significantly. According to the Engineered Wood Association (www.apawood.org), LVL production has increased 360 percent since 1980, to an output of 86.3 million cubic feet last year. It is one of the fastest growing non-panel engineered wood products available today.