New Ideas and Materials are not quickly adopted in the construction industry. Folks tend to do things and to use that which they have become familiar. This, unfortunately, tends to slow down advancement and change in the industry.

One example is the use of OSB sheathing verses the “good-ol” CDX plywood. I still find, in 2011, some builders who have never used nor plan to use OSB. When asked why, their answers seem to boil down to a few false ideas. Without further evaluation many dismiss OSB because they have seen the result of water damage to particle board in cabinet countertops. They remain convinced that OSB is similar and will come to pieces in high moisture. There is also, to some, a question of strength. How could a bunch of wood fibers that are pressed together be as good as the old standby, CDX plywood?

I was a bit skeptical myself when I first came across OSB as an option – several years ago. However when I took a look at the product I had to admit it was quite well worth the try. I\’m going to go over a few myths that I have heard regarding OSB – but first let\’s cover 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 (meaning Oriented Strand Board) is produced by taking small fibers from smaller, low diameter trees and bonding them with a resin, heat and pressure. These panels achieve excellent 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, and when folks compare the prices of OSB and Plywood (OSB sometimes costing half as much) this is usually the deciding factor.

I think it is a good idea to be on the lookout for newer and better materials and techniques – especially in construction. OSB is relatively new and I very much recommend it for any type of construction project.

Ken Risley, the Engineer Designer, is author of many construction and design articles. He provides personalized help in planning, design, engineering and construction plans and can be reached through his website.