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New Generation OSB Sub-flooring

A lighter sheathing panel, less prone to thickness swelling


Oriented strand board (OSB) is rapidly displacing plywood as the most common sheathing material for walls, roofs, and floors. OSB's advantages include lower cost, greater stiffness, and uniform strength. However, some builders and other users have complained that OSB is subject to strand delamination and edge swelling if it is exposed to too much moisture during the construction cycle. Recently, manufacturers have developed more durable OSB sheathing and subflooring products that provide extended warranties and performance guarantees, to control delamination and swelling.

OSB is an engineered sheathing panel created from layers of wood strands approximately ½-inch wide by 6 inches long. The strands in the outer two face layers are roughly parallel with the longitudinal axis of the panel, while the strands in the core layers are perpendicular to the longitudinal axis. In fabrication, the strands are first coated with resin, then oriented in the desired direction within a layer. The mat is then pressed under heat and pressure to form a panel. The panel is then cut to final dimensions, and packaged for shipment.

New-generation OSB uses special isocyanate resins that provide adhesion of the strands without overly compressing them. The result is a lighter panel, less prone to thickness swelling. J.M Huber AdvanTech®, Louisiana-Pacific Top Notch®, and Weyerhaeuser Structurwood® Edge, are considered as a "New generation" OSB. Other features employed by some manufacturers include edge sealers, to exclude water intrusion from the side of the panel, and special channels or notches, to facilitate water removal and drying.

Several companies report adequate supplies of OSB ready for immediate delivery. All manufacturers provide square and tongue and groove edges and offer thicknesses from 19/32-inch up to 1-1/8 inches. Panel dimensions are usually 4 feet by 8 feet, although special mill orders are available.


The cost of this material is still cheaper than plywood, so it is easily available to anyone seeking to utilize it.

Quality and Durability

The newer OSB is more resistant to swelling from moisture, resulting in less of a chance of rotting and a longer life.


While OSB is not suitable for all woodworking applications, it is widely used for roof and wall sheathing, and floor decking. Improved moisture resistance should improve its current wide acceptance. Utilizing the newer OSB should not change the construction process at all.

The New Generation OSB can cost less than plywood. A 4 feet by 8 feet by 23/32-inch panel costs about $18.

Regardless of its resistance to moisture, it is wise to periodically check to ensure that no damage is caused to the OSB from moisture, etc.

New Generation OSB conforms to APA PS2-92 performance standard and also to HUD/FHA Use of Materials Bulletin No. UM-40c. These panels are accepted by all major building codes.

Not Applicable

"New Generation" OSB installation guidelines are similar to conventional OSB. Screws, nails, staples, and glue are all approved fastening methods for OSB installation. Refer to manufacturers' literature for specific instructions or specifications. Manufacturers claim that the moisture-resistant properties of the panels eliminate the need for sanding prior to the installation of the finish floor.

Varies with manufacturer. One manufacturer offers a 50-year guarantee against manufacturing defects.

OSB products have been well accepted by builders, because they are less expensive and more consistent than the plywood products they replace. The main benefit of New Generation OSB products is their improved durability and resistance to swelling and delamination, when exposed to rain before they are enclosed. One manufacturer offers a 50-year guarantee against manufacturing defects.

There are environmental advantages to OSB as well. Plywood places a large demand on mature forests because it requires large diameter trees for veneer slicers to efficiently operate, OSB can be created from low-value, small-diameter trees, saving higher-valued species and older-growth forest.

Disclaimer: The information on the system, product or material presented herein is provided for informational purposes only. The technical descriptions, details, requirements, and limitations expressed do not constitute an endorsement, approval, or acceptance of the subject matter by the NAHB Research Center. There are no warranties, either expressed or implied, regarding the accuracy or completeness of this information. Full reproduction, without modification, is permissible.