Oriented Strand Board

 Oriented Strand Board Subfloor InstallationOriented Strand Board (OSB) is a popular and durable paneling product. In the USA and Canada it’s often made from strands of aspen and poplar, or other such hardwoods; that have been bonded together under high heat and pressure with a waterproof adhesive.

The use of the term strand here is in the context of a wafer or small thin sheet of material and the term ‘oriented’ denotes that the outer ‘strands’ of a panel are arranged to run lengthwise along it, similar to the construction of a plywood, making it strongest along its length, compared to the width.

Making Oriented Strand Board Panels

The individual strands used to produce an OSB are typically less that 150mm (6 inches) long, 25mm wide (1 inch) and are wafer thin at about 1mm (1/32 inch); they are sliced from small diameter round logs that have had their bark stripped off. Each panel is comprised of several layers or mats of strands.

The orientation of the strands is automatically done by a machine for each layer or mat, the orientation is simply set as the direction the material passes through the machine. The strength of the panel comes from the cross-orientation of the mats, the outer layer strands being oriented in the same direction; whilst the application of a reliable and strong resin bond completes the strengthening process.

Panels of OSB can be manufactured and cut to varying thicknesses and dimensions, according to the job they’re needed for. Most panels are between 6mm (1/4 inch) and 25mm (1 inch) thick, the commonest panel size is 1220 x 2440mm (4 x 8 feet), but can be produced in panels up to 8 x 24 feet.

Uses of Oriented Strand Boards

Since their introduction in the 1970s OSBs have become a popular replacement to plywoods in the construction industry. With a high degree of strength, rigidity and water resistance OSBs can be put to many uses including: rim boards, stair treads, sheathing and for concrete formwork.

When treated with a fire retardant they can also be used in wood flooring, walls and as a base for roofing materials. With an added foam insulation core they can be used as ‘outer-skin structural’ panels, whilst pre-fabricated wood I joists can also be made from them. All OSB panels are easily cut and worked with ordinary manual or powered carpentry tools.

Care of OSB Panels

Although strong and durable, OSBs need storing and handling correctly. Whilst being stored before use, they should be protected from getting unnecessarily wet; so store them under cover and off the floor. Whilst they can be stored vertically, storing them horizontally is probably best.

If they’re ‘tongued and grooved’ panels - definitely store them horizontally and protecting the edges and corners becomes especially important. Although the panels are treated with water resistant chemicals, when installing OSB panels you need to allow for the panels to expand. Most OSB panel manufacturers recommend a 3mm (1/8 inch) gap between the panels for this purpose.

Read the Labels

OSB panels may have several stamps on them form the manufacturer or retailer. One of those stamps will have a vital piece of information on it, which if you’re new to OSBs you’ll need to read. Whilst experienced workers with OSB panels can tell which direction the maximum strength can be obtained it might not be apparent to everyone else all the time. To help with this the manufacturer will have stamped the panel telling you, amongst other things, the direction of the surface strand alignment. This is usually at the bottom of the TECO label.

Photo by Garrulus, Creative Commons Attribution License