By Paul Bianchina
Your local lumber yard is definitely a different place from the one your parents and your grandparents visited. An area once dominated by big wood timbers and endless stacks of solid lumber sawn from massive trees, today's yard has an increasingly diverse selection of structural materials made from previously-unusable small growth logs. Some of these products you've probably used or at least seen in the stores, while others may be completely new to you. Here are just a few of them:
Panel Products
Plywood, a building material that virtually every homeowner has used at one time or another, is probably the earliest type of engineered lumber product in existence. A composite of thin sheets of wood peeled off a log, called veneers, that are stacked and glued together under heat and pressure, the resulting sheet is considerably stronger than the total strength of the individual layers.
Oriented strand board (OSB), often referred to by the generic names "waferboard" or "chipboard," is another engineered panel product that many people are familiar with, particularly for wall and roof sheathing. Small diameter logs are ripped into long thin strips, then clipped into strands approximately 3 1/2 inches long. The strands are dried, coated with resin, then oriented into three or five layers, each layer perpendicular to the ones above and below it. The layers are pressed up under heat and pressure, and the resulting sheet is strong, stable and rated by the American Plywood Association for a variety of structural applications.
A hybrid of these two is Com-Ply, which utilizes a standard veneer top and bottom face that is oriented to the long dimension of the panel, and a core of OSB. The resulting sheets have good stability and load-bearing capabilities with no "hollow spots," called core voids, than are found in some plywood. Com-Ply products are used for subfloor applications, and are also commonly made up into sheet siding in a variety of standard patterns.
Lumber Products
In the place of solid-sawn lumber is a growing variety of engineered lumber products with superior strength and virtually unlimited length, all made from small, fast-growing second- and third-growth trees with less impact on the environment. Some of the more common ones include:
- I-Joist: Engineered lumber I-joists have gained tremendous popularity in recent years as the quality and stability of standard sawn lumber has diminished. The I-joist uses a top and bottom flange of conventional lumber or an engineered product such as LVL (see below), sandwiched to a center web of plywood or OSB. The resulting product is exceptionally strong and light-weight, with none of the warping or shrinking associated with standard lumber. I-joists can span long distances without intermediate support, and are commonly used as floor joists, ceiling joists and, increasingly, as rafters in a variety of roof-framing applications.
- Laminated veneer lumber (LVL): Like plywood, LVL begins as thin wood veneers peeled off a log. The veneers are cut into strips ranging from 27 to 54 inches wide, dried and coated with adhesive, and then stacked several layers thick with the grain all running in the same direction. The stack is pressed and dried, then cut to length, forming long, dimensionally stable lumber for a variety of framing applications.
- Parallel strand lumber (PSL): Once again, PSL begins with veneers. The veneers are then clipped into thin strands four to eight feet long, then sorted for defects, coated with adhesive, aligned parallel with one another and pressed up into long, thick beams - typically 11 x 17 inches and up to 66 feet long. There are over 3500 individual wood veneer strands in 8 feet of PSL beam, making for exceptional stability and strength for a variety of long-span, load-bearing uses.
- Laminated strand lumber (LSL): LSL utilizes small logs that are cleaned, debarked and then cut into small, thin strips about 12 inches long, called strands; as much as three-quarters of the log is processed into usable material. The strands are glued and formed into loose mats, then pressed using a steam-injection process that creates massive, high-strength beams up to 8 feet wide, 5 1/2 inches thick and 48 feet long.
All of these engineered lumber products - and many more - can now be found in stock or through a quick special-order from virtually all lumber yards and home centers.
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