Wall, Floor and Roof Sheathing - Plywood or OSB?

Sheathing is the material that covers the frame on the outside of a home (walls and roof).  Sheathing is usually made of plywood or Orientated Strand Board (OSB).  OSB is made of small chips of wood that are glued together.  In OSB, the wood chips are placed at angles across various levels.  Plywood is made using layers of wood veneer glued together so that the grain of each veneer layer is at different angles.  The angles used to place the strands or veneer helps give these materials strength.  Plywood is usually a little stiffer than OSB and may provide a little more strength for the same thickness..

One benefit of OSB is it costs less than plywood.  Also OSB helps conserve environmental resources because it uses wood particles.  OSB is becoming more widely used then plywood and plywood may be harder to obtain in some areas.

OSB is not the same as particle board, waferboards, flakeboards, or fiberboards.  Those other types of materials may look similar to OSB but those materials are inferior to OSB.

Plywood holds nails and screws better than OSB and OSB is more likely to swell if it gets rained on.  When swelling occurs it can loosen the nails fastening the OSB to the frame.  If rain or snow may occur in your area during construction then it's a good idea to use plywood or OSB that has a rating of "Exposure 1".  This means that the sheathing is made with waterproof glue and resins and will hold up better under wet conditions.  Exposure 1 materials can hold up fine for the few weeks they are exposed to possible moisture during construction.  Also, it's a good idea to protect the materials from moisture during storage and construction.  If the plywood or OSB is going to always be exposed to the exterior then get materials that are rated as "Exposure".  The ratings are stamped on the materials.

When swelling occurs in OSB the swelling typically happens around the edges of the material.  OSB manufacturers usually treat the edges of OSB to help resist swelling.  However, builders sometimes cut OSB boards and don't treat the edges of OSB that have been cut.  These untreated edges are more likely to swell.

Plywood tends to absorb water faster then OSB but plywood tends to be more forgiving because plywood dries out faster and swells less.  Because of this plywood may be a better material to use in places that may experience more humidity (such as floors over crawlspaces or in attics).

The quality of OSB tends to be more consistent than the quality of plywood.  This is because plywood may have spots with knots or gaps.  Because of this a floor that has an OSB subfloor may be quieter or feel more solid then a floor with a plywood subfloor.  However, because of a greater risk of swelling, some manufacturer's warrantees on roofing materials or floor coverings (especially ceramic tile, or vinyl) may require plywood to be used.  In areas that have hurricane force winds local building codes may require plywood for roof sheathing.

Plywood can be treated for fire resistance or moisture resistance better than OSB.  This is because the strands of wood in OSB are covered by more resins and are more difficult to treat.  If you plan to treat the home with fire resistant or moisture resistant chemicals then plywood may be a better choice over OSB.  OSB is also heavier then plywood and its weight can make it more difficult to work with.

Plywood is usually made of either yellow pine or fir.  Yellow pine costs less.  Fir is usually a better wood to work with and may be more resistant to moisture damage from rain.  However, fir wood is becoming more scarce and may not be available in some areas.

In summary, the quality of OSB and plywood is very similar ant they are both fine to use as wall, floor and roof sheeting...