Basic Manufacturing Process of OSB

Since the mid-1980s, oriented strand board (OSB) has been one of the most commonly used engineered wood-based panels for structural construction in residential sectors in North America. OSB was first produced in Canada in 1964, but it did not find its solid status in the market until the mid-1980s.

The number of OSB mills increased by more than 50 percent from 1990 to 1997. Today, total OSB production in North America is approximately 706 million ft3 (20 million m3), and there are about 20 companies that manufacture OSB in the United States, Canada, and Europe.

 Oriented Strand Board

Forest products companies are utilizing raw materials more efficiently with better technologies in more environmentally friendly ways. With this approach to managing forests, engineered wood composite products such as OSB have gained a significant role in the world market. A decline in plywood manufacturing in many countries, due to limited large log supplies and environmental concerns, will increase the production of OSB in the future. OSB production is expected to continue to increase in North America and Europe and have the main share in the structural wood composite market.

This fact sheet summarizes the basic manufacturing steps of OSB and some of its properties as a building material.

Basic Manufacturing Process of OSB

OSB is manufactured from fast-growing, small trees. West Coast inland mills producing OSB primarily use lodgepole pine logs averaging 10 to 12 inches in diameter at the breast height (DBH). Mills in the South use pine plantation thinning, Southern Pine, and soft hardwoods species such as aspen with an average DBH of 8 inches.

Short segments of the logs are washed and debarked prior to strand production by using disk or ring-type flakes. Generally, strand size is approximately 0.5 inches by 3 inches by 0.02 inches depending on the type of process and raw material. The size of the strands can be modified based on the target specifications of the panel.

 Oriented Strand Board     

Since the moisture content of the strands ranges from 40 to 75 percent, they have dried to 5 to 10 percent moisture in large, rotating single-pass or triple-pass dryers with an inlet temperature of as high as 1,250oF.

Dried strands are classified into two sections using various sizes of screen. Larger strands are used for the face layers while the smaller strands are laid out in the core layer. Face and core layer strands are mixed separately with an exterior binder in a drum-type rotating blender. Depending on the process, a certain percentage of wax and other chemicals also can be applied during the blending process.

Applications of OSB

OSB is extensively used for wall sheathing, floor underlayment, roof cover, and I-joist in both commercial and residential buildings. OSB also is used in furniture, reels, trailer liners, and recreational vehicle floors.

Similar to other wood products, OSB also is prone to decay when conditions are optimum for biological microorganisms, such as fungus. Zinc borate and oxine copper are sprayed as fungicides to enhance the resistance of OSB to biological deterioration. In general, OSB is not used for applications where there is direct contact with a moisture source, such as soil. However, brief periods of exposure to rain during the installation of OSB in residential construction should not cause any significant problems in terms of its dimensional stability.

It is recommended to leave a 1/8-inch gap between panels during installation to prevent possible buckling due to expansion. Most OSB panels also are treated with a sealant on the panel edges to reduce moisture penetration during the service life.