November/December 1992

Volume 1, Number 3

Laminated Strand Lumber Product Introduced

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Laminated Strand Lumber Product Introduced

Trus Joist MacMillan, makers of the Silent Floor™ framing system, have just introduced a rim joist made especially for use with that system. The new product is made from a new type of manufactured lumber called Timberstrand LSL™ (Laminated Strand Lumber), which is basically a next-generation, high-end oriented strand board (OSB). The new rim boards are 11/4" thick, and come in widths matching those of TJM’s I-beam joists. The standard lengths are 11' 8" and 17' 6", and the retail cost for the 117/8" wide board is about $1.25 per linear foot.

Dave Wooden of Brownsburg, Indiana is one of the first builders to have used these boards, which are only now reaching retailers in many parts of the country. When asked about the product, he sounded enthusiastic. “I really like it. It’s much easier to deal with, and saves lots of time ripping down plywood.” Unlike the 3/4" plywood commonly used for rim boards, the Timberstrand product is thick enough to nail the floor decking into, which helps to tie the house together.

The rim joist is only one minor product for the huge new Timberstrand LSL facility in Deerwood, Minnesota. The biggest potential markets for the new material are wood window and door manufacturers, who are seeking alternatives to solid, clear wood, for use in clad windows and veneered doors. The Deerwood plant manufactures Timberstrand LSL into huge billets, 35' long, 8' wide, and up to 51/2" thick. These billets can then be milled to any size, without the defects and waste associated with real lumber. To make the material, whole aspen logs from forests near the plant are peeled and then shaved into long, thin strands. After drying, these strands are mixed with an adhesive resin and shaped into large mats. The adhesive cures as the mats are injected with steam and pressed into shape. Bark from the trees is burned to generate heat for the presses.

From an environmental standpoint, Timberstrand LSL provides an alternative to old growth timber for some applications. A plentiful, fast-growing, and otherwise underutilized species, aspen, is used instead of centuries-old trees. The company carefully sited the plant where an adequate supply of aspen could be provided indefinitely from the surrounding 13-county area. By clearcutting aspen stands on a rotating basis, the tree will constantly regenerate from the root systems, reaching maturity in about 30 years.

Some environmentalists point out that aspen is not the area’s naturally dominant species, but a pioneer species. As such, it would be succeeded by higher-value hardwoods, primarily sugar maple and basswood, if it weren’t harvested. The area is currently covered with aspen because it is in the first stages of returning to forest from recent agricultural uses. Dr. John Kotar, a forester at the University of Wisconsin, reasons that for the sake of biodiversity the best case would be a balance of regularly harvested aspen (harvesting replaces the fires that used to clear the area periodically), with areas that are allowed to mature into other species. It is not clear if TJM’s timber requirements will allow such diversity.

Another concern some people have regards the adhesives used in manufactured lumber products. The resin used in Timberstrand LSL (MDI polyurethane, also called isocyanate) has no formaldehyde, so off-gassing once the product is installed should not be an issue. (It is the same adhesive used in Louisiana-Pacific’s “formaldehyde-free” OSB products.) Before it is cured, however, MDI is highly toxic, and a likely carcinogen. To protect workers, the areas in the plant where the adhesive is used are sealed off, and the pressing process is all remotely controlled. Overall, the new plant is built with state-of-the-art pollution controls and almost no emissions of any sort.

Trus Joist MacMillan is a 51%/49% partnership between Trus Joist International and MacMillan Bloedel Ltd. All of the former Trus Joist Corporation’s activities except for its window subsidiaries are now owned by the partnership, which also owns the Parallam PSL facilities formerly belonging to MacMillan Bloedel. Trus Joist MacMillan, 9777 W Chinden Blvd., Boise, ID 83714, 208/375-4450; 378‑4754 (fax).

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November 1, 1992