APA: Engineered Wood Products
What is Engineered Wood?
- Engineered wood is a relatively new term that means just what it says: wood products that are engineered for specific performance characteristics.
- Plywood is considered to be the original engineered wood product and has been used for structural applications since the 1940s.
- Since then, other products have been developed which fit into the engineered wood family: OSB, glued laminated timber (glulam), composite panels, wood I-joists and laminated veneer lumber.
- Engineering occurs during the manufacturing process. Wood components are combined in specific ways with adhesives to form structural members that perform to established standards set by APA and other certification agencies.
- Many engineered wood products are used in the construction of buildings, while some are used in other engineered applications such as materials handling and transportation, and even for the construction of road bridges.
The first generation of products
Plywood
- Plywood is the original structural wood panel. It is composed of thin sheets of veneer, or plies, arranged in layers to form a panel. Plywood always has an odd number of layers, each one consisting of one or more plies.
- Adhesive is applied to the veneers. These plies are then laid up with their wood grain orientated perpendicular to the other layers. By alternating grain direction between adjacent layers, strength and stiffness in both directions are maximised, and shrinking and swelling are minimized.
Orientated Strand Board
- OSB is a structural, performance - rated panel product made with wood strands that have been layered and orientated at various angles to one another in order to maximize panel strength and stability. The strands are then bonded with phenolic resins.
- Manufactured to be used in the same residential and commercial applications as plywood, OSB brings many benefits to the designer and end user. For instance, OSB’s manufacturing process allows for a uniform, consistent panel which is free from core voids, knotholes or other natural imperfections.
The next generation of engineered wood products
- The new generation of engineered wood products make even more efficient use of timber resources.
- Environmental issues are currently of major concern to the wood products industry. In the US, a battle is being waged over the allocation of timberland and multiple use management and it is APA members who are setting a lead.
- Not only do they appreciate the need to utilise resources in an efficient manner but have been instrumental in bringing about changes to both products and manufacturing techniques which enable mills to reduce raw material requirements and take advantage of more plentiful species.
- Particularly when using veneer to produce a solid timber product, manufacturers are able to make better use of smaller, second generation trees and thereby reducing the pressure on the larger more established forest areas.
Wood I-Joists
- I-Joists, also referred to as wood I-Beams, are structural load carrying products for roof and floor joist applications. Their ‘I’ configuration provides high strength and stiffness in long lengths with low material weight.
- The flange material for I-Joists can be stress graded dimension lumber or LVL; the web material OSB or plywood.
Laminated Veneer Lumber (LVL)
- One of the most important recent developments in timber technology has been the introduction of Laminated Veneer Lumber (LVL). It is already used extensively in the US, where the majority of manufacturers are located.
- When compared to steel, LVL has the advantage of being much lighter in weight which gives it a superior strength-to-weight ratio. LVL’s improved strength is its ability to disperse natural growth characteristics such as knots, splits and grain slope and minimise their effect on the product’s structural integrity.
- With its greater load capacity and ease of handling, LVL is ideal for beams, lintels and a variety of long-span applications. It is manufactured to full dimension which eliminates the need for labour-intensive shimming and its multi-ply configuration means LVL has all the advantages of wood products without the disadvantages like shrinking, twisting and splitting.
- The manufacturer of LVL is a sophisticated and precise operation which begins with the drying and grading of veneers. Both visual and ultrasonic grading methods are employed at this critical stage in the process.
- A waterproof phenolic adhesive is then applied to the selected veneers prior to the actual lay-up process.
- The coated veneer is arranged with the grain direction running parallel to adjacent veneers and is inserted into a continuous press where heat and pressure activate the adhesive. The LVL is now permanently bonded and can be cut into the desired lengths.
Parallel Strand Lumber (PSL)
- The manufacture of PSL is similar to that of both LVL and OSB . To make PSL, long veneer strands are bonded together with waterproof adhesives in a parallel formation to produce beams.
- As with LVL, parallel strand lumber also carries a high fibre bending stress. This product can be used in beam and lintel applications where high bending strength is critical, such as floor girders.
Glued Laminated Beams
- Glued laminated beams, or glulams, are manufactured by end-gluing dimensional lumber such as 2x4’s or 2x6’s into continuous plies. These plies are then face-glued with waterproof adhesives, formed under intense pressure, and finished.
- Glulams are used in a wide variety of residential and commercial applications such as girders and purlins, ridge beams and roof rafters.
ENDS
APA-The Engineered Wood
Association is widely recognised as a world authority in engineered
wood products. It is a non-profit making trade association representing
manufacturers of plywood, OSB, glulam, I-joists and laminated veneer lumber
(LVL).
APA provides a comprehensive online technical service on the
uses of engineered wood specifically for the European market which includes a
list of brochures available free of charge as downloadable pdfs. These can be
accessed on apa-europe.org. A full list of downloadable technical material is
available on www.apawood.org.
APA member mills produce approximately 70% of the structural
panel products and over half the glued laminated beams manufactured in the US.
It also represents a significant number of Canadian OSB producers. One of APA’s
most important functions is quality inspection and testing. It maintains five
quality testing laboratories in key production regions, and a 3,400 square metre
research centre at its US headquarters in Tacoma, Washington State.
APA-The Engineered Wood Association
7011 South 19th Street
Tacoma
WA, 98466
USA
Tel: +1-253-565-6600
Fax:
+1-253-565-7265
e-mail: kevin.hayes@apawood.org
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