Oriented Strand Board (OSB)
PJ Fitzpatrick, Inc. A Green Contractor
What is OSB? OSB is made from wood ground into thin wood strands. These strands are mixed with wax and adhesive and then hot pressed. Approximately 50 layers of strands make one sheet of OSB. Mostly used as roofing materials by local contractors.
Oriented Strand Board: The Future
Since its debut in 1978, OSB has been rapidly accepted. In fact, in many areas of North America, OSB has virtually replaced other panels in new residential roofing construction. Today, all model building codes in the U.S. and Canada recognize OSB panels for the same uses as plywood on a thickness-by-thickness basis, and is a favorite of local contractors.
Advantages of OSB over Plywood
- OSB is generally more square and has smaller dimensional tolerances, great for roofing.
- It can be manufactured into panels of up to 8′ x 24′, far larger than plywood
- There are no soft spots such as those that can occur in plywood
- OSB is made from smaller (often farmed) trees reducing the demand for old growth timber.
- OSB has greater shear strength than plywood; the span rating, nail pull and screw hold are all roughly the same.
- It can be less expensive than plywood. For a typical 2400 square foot home, OSB will save money if used as the sub floor, sheathing, and roof decking instead of plywood.
- 50 strands thick, so its characteristics are averaged out over many more “layers” than plywood.
- Consistently stiff. Plywood has a broader range of variability.
OSB and the Environment
Choosing the right structural panel means more than checking performance specifications. The concern for energy efficient and environmentally sound building products is a growing priority – both to you and your customers. As the only truly renewable building material, wood is increasing its reserves every year. Therefore oriented strand board is the natural solution to this challenge.
- The fiber for OSB is grown in sustainable forests and tree farms.
- The manufacturing process uses nearly 90% of the log, with the balance used to supply energy to mill.
- OSB is environmentally responsible. It takes far more energy and resources to produce steel, concrete, or other roofing or building materials.
- Modern mills – costing more than $150 million – are scientifically designed to meet or exceed strict quality standards for environmental safety.
- OSB is safe to use. Resin binders and waxes are completely cured and stabilized, so there is no measurable off-gassing from panels. roofing contractors prefer this product for it’s nationally recognized safety record.
OSB Manufacturing Process
After harvest, whole logs are hauled to the mill’s wood yard, then sorted.
Logs are soaked, to remove ice and prepare wood for stranding, then sent up the jack ladder.
Logs are run through the debarker to remove bark. Bark is later used as fuel in the mill’s energy supply.
The strands are cut from whole logs into precise dimensions of up to six inches long.
Strands are deposited into wet bins.
Strands are then dried until the appropriate moisture content is reached.
Strands are blended with resin binders and a small amount of wax, which improves the efficiency of the resin binder and enhances the panel’s resistance to moisture and water absorption.
Strands go through the forming line where cross-directional layers are formed.
Layers of cross-directional strands are pressed under intense heat and pressure to form a rigid, dense structural panel of oriented strand board (OSB). Presses are primarily multiple opening allowing 8 to 16 master panels to be pressed in one operation for increased efficiency.
Panels are cooled, cut to size, stamped, stacked in bundles and edge coated. All graded panels bear a mandatory certification agency stamp, plus the SBA logo if applicable.
Finally, the panels are ready to be loaded and shipped to destinations around the world. Panels can be ordered smooth sanded for special uses or with tongue and groove edges.
