In my years in this business I have observed that the building profession tends to be resistant to new ideas and techniques. The tried and true methods seem to endure even as newer materials and techniques are developed.

One area where this is evident is in the use of OSB as a sheathing material versus the more traditional CDX plywood. Even in 2011 one will find many who refuse to use OSB for one reason or another. Most make such conclusions without really evaluating the details. It is easy to confuse OSB with the particle board that we have seen expand and deteriorate when exposed to moisture. Some question the strength of OSB.

I, too, felt that way for many years. Then one day I took a look. I want to discuss a few popular myths about OSB. But first a few definitions:

Sheathing – When we say \”sheathing\” we are talking about the action of placing a large stiff sheet of something over several framing members to tie them together. This is sometimes called a diaphragm.

Traditional plywood is a flat sheet of layered veneers of wood. Each layer has a strong direction and a weak direction based upon the grains of the wood. The layers are alternated to achieve strength in all directions. We often see the term CDX plywood. This simply indicates the quality of the finish (C and D are pretty rough) and the X indicates its for exterior use.

OSB means Oriented Strand Board. It is produced by taking many fibers of small, low diameter and relatively young and fast harvesting trees and bonding them together using thermal resin and pressure into a panel with good strength in all directions.

Myths:

Myth 1 CDX plywood is stronger than OSB. Nope. Interestingly, all testing standards and building codes consider the two materials (OSB and Plywood) as structurally equivalent.

Myth 2 OSB will expand and deteriorate like particle board. This is not true. OSB and particle are not the same at all. OSB is actually better suited for longer periods of direct exposure to rain than CDX plywood. This can be important when we get the plywood installed and are not able to cover it in time for that early summer shower.

Myth 3 Plywood is just better than OSB and its what I have always used. I would never suggest anyone changing against their own certainty however my experience is that such considerations do not stand up to evaluation. If one looks one will likely conclude that plywood is not \”better\” than OSB. Factually OSB is made from younger and smaller fibers and are actually faster to product when one includes the growth of the wood. There is great consistency in the product and it is more stable, in dimension, than plywood when exposed to moisture.

Today OSB is used in about 70% of the homes built in the U.S.. I specify it in my own designs and in my own building projects unless instructed otherwise by my client. When my client has such an opinion, I show him or her the facts but then let them make the final call.

Oh, I failed to mention, OSB can cost about half as much as plywood. This fact alone may be enough reason to make the switch from plywood to OSB.

I believe that all of us should be open to newer and better ways to build our homes and buildings. OSB is one of those methods that I readily endorse.

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