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Facts on Plywood, OSB

July 07, 1996

As a general contractor in Southern California for 19 years, and a construction litigation expert witness for the past five years, I have read your ongoing "Your New Home" series of articles with great interest.

Most of the points raised by the authors of the June 16 article headlined "Hiring Builder? Check Out the Subcontractors" hit the proverbial nail right on the head, but their comments on exterior particle board versus plywood sheathing contain several inaccurate statements.

The correct name for the "particle board" they refer to is "oriented strand board" (OSB). Plywood is not a single sheet of wood, as the authors state, nor is particle board really pieces of wood glued together.

Where plywood obtains its strength from various numbers of plies of thin strips of plywood veneers glued together in alternating perpendicular orientation (similar to the orientation of the noodles in a deep dish lasagna), OSB obtains the same structural effect from the use of wood chips in lieu of veneer strips.

It is true that OSB is cheaper than plywood; however, when installed as recommended, it performs as well as plywood. OSB has several other advantages: It provides a smoother surface than plywood and will not buckle or ripple as much as plywood if it should get wet.

The article also states that there should be no gaps between exterior sheets. That is incorrect. Good practice, and local codes, require that a small gap (about one-eighth of an inch) be left between sheets to allow for possible expansion of the individual sheets.

The most important thing for the concerned homeowner to verify is that the plans allow the use of OSB, and that the OSB has the mill mark stamps stating that the material is certified by the American Plywood Assn. or other similar certification organization.



Schaffel Development Co. Inc.

Van Nuys

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