Building A Home? Should You Use OSB Or Plywood Sheathing?

by Engineer Designer on November 9, 2011

The Building Profession is traditionally slow to change and adapt to new methods and materials. 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 is used to stiffen a group of parallel framing members to keep them from racking. It is sometimes called a diaphragm. Plywood is a flat sheet of wood that is quite strong because of the way it is made. It consists of layers of wood (thin veneers) which are laminated together in alternating grain orientations. Since wood has a weak direction and a strong direction (relative to its grain pattern) these layers contain wood turned in different directions to gain strength in all directions. CDX plywood is a designation indicating a rough finish and a glue that is okay 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 OSB lacks the strength of CDX plywood. This is untrue. All building codes and dictating standards make no differentiation between OSB and plywood. For sheathing, they are considered structurally equivalent. Myth 2 - OSB will fall apart like particle board. This is untrue. Many have observed kitchen cabinets (many are largely made of covered particle board) which expand and even crumble after exposure to moisture. This would be quite unacceptable for a structural member of a home or building. However particle board is different than OSB in that it is not produced for exterior use. The truth is OSB is designed for longer exposure to exterior higher moisture conditions than even CDX. 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. OSB has proven itself in the industry and is used in about 70% of homes in the U.S. I now specify it in my own designs and on my own projects unless the owner really insists on plywood. When this occurs I always make available the facts but will go with plywood if he or she chooses. Oh, and when folks compare the prices of OSB and Plywood (OSB sometimes costing half as much) this is usually the deciding factor. 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.
  Imagine this: You are building a home with either on your own or with the help of a general contractor. The project is finished and you take possession and move in as a happy owner of a brand new custom home.   You have faithfully paid every bill that was due. You finally pulled it off. It’s done.Then, out of the blue, you get notice that your brand new home has been slapped with a lien (a legal claim against your home for an amount stilled owed) for sums still owed for some materials or labor (or both) for which you are certain you have already paid.   How would you feel? Violated? Like after a burglary? You bet you would. After checking further you find out that one of the material or labor suppliers, a company that you may never have heard of, supplied products for your home and was never paid. Of course you paid your bills. But the guy you were paying did not. And that person is gone!   You might say, “That shouldn’t be my problem!”. Not correct. It is your problem.   The good news is that there are ways to avoid this painful situation. Here are a few suggestions (the last one most important):  
  •  If you are the owner-builder (ie. contracting your own home) make sure you know how every subcontractor (“sub”) who you hire is hiring their own labor forces and from whom they are obtaining materials. This may be tedious, but it is worth knowing. Your checking will put the sub on notice that you are watching. Find out if his workers are employees or is he sub-contracting (“subbing”) to them. If he is subbing, each sub has the legal right to lien your property if he or she is not paid. If they are not paid by the sub, they can come after you – even if you paid the sub.
  •  If you are the owner-builder be sure to have a written contract with each sub. Do not go for “hand-shake” deals. If he is supplying materials as part of his agreement find out who the supplier is. Contact the supplier and make sure that the sub has an account which is up to date. If no account, then he is likely paying cash for the material which is totally fine.
  •  If you are the owner-builder, when you pay a sub, get a release of lien from them and an affidavit that they have paid for all labor and materials that were part of their contract with you. This affidavit may not be worth much but it is another assurance that you can us. The above two and the next one are the most important.
  •  And the last point, likely the most important, applies, whether you are the owner-builder or have a contractor who is building for you. All subs and material supplier who are not in direct contract with you are required, by law, in most states, to supply what is called a “Notice to Owner” document to you before they can place a lien on your property. This is a legal notification, sent to you by certified mail, that they are supplying materials or labor, or both, to your new home. So you should check your legal address routinely, during construction, and watch for these documents. There are certain time requirements and you should check your local state laws to determine these. Once that time has passed they can not lien your home, regardless if they were paid or not. If you get such a notice pay attention. Assure that that entity is paid before releasing funds to your contractor or sub. If he can’t do it, then double-party checks can work. You can find a way. Just remember that it is, ultimately, your legal responsibility to assure that these folks are paid.
        Know the players, know the laws and pay attention. Awareness is the key.   Have fun.
I am often asked by my clients if we should use a masonry exterior wall or one that is framed in wood. Masonry walls consist of concrete blocks stacked up from the slab to the full height of the wall. They are placed in beds of mortar and strengthened with embedded reinforcing steel and hollow cores full of concrete. The strength is dictated by wall thickness, height and density of reinforcement and, of course, loading conditions. Framed walls consist of wood studs usually 16" on center with a stiff sheathing material, water proofing and some sort of siding on the outside such as stucco or siding. Let me answer a few common questions: Can termites be a problem in wood framed homes? If the framed wall is built correctly the answer is "no". Pressure treated plates are used at the bottom of the wall. Termites hate PT wood and won't eat through it. Also termite shield should be used. This is like flashing and is placed under the wall and extends out to block passage of subterranean termites in their attempts to travel up the wall. Those and routine maintenance, after construction, such as inspections and treatment allow homes to last a long time. There are many framed homes that are several centuries old which stand as proof that such construction methods are valid. Is a masonry wall stronger than a framed wall? In general, a framed wall can be built with adequate strength to handle hurricane winds and other forces. A wooden wall with proper sheathing, nailed properly, is quite strong. A masonry wall is also quite strong. Its strength is a function of its thickness, its height as well as the reinforcement used. What about Cost? Would masonry or framed walls be cheaper in the long run? Siding for a framed home can cost more than the typical stucco finishes used over block walls. However other factors, including speed of construction, cost of materials and labor tend to make framing an overall less expensive approach. What about insulating masonry walls and framed walls? Insulation is always a challenge with masonry walls. The blocks themselves are not good insulators. Insulation is usually achieved by placing a foil over the pressure treated furring strips, or foam sheets over the wall and can even include filling the cores with insulation. None of these achieve insulation as high as that achieved in a wood wall. Wood framed walls are usually insulated with batts ranging from R-11 right to up in the 20's, depending upon wall thickness. Wood is generally easier to insulate to higher levels. One advantage of masonry is that it has a higher thermal mass which will tend to regulate temperatures a bit better. Does the relative thickness of masonry walls take up more room in the house? If one uses a standard 8" masonry block and compares it to a typical 2x4 exterior wall, one can instantly see about a 5" different in the amount of each exterior room that is taken up by the wall. Framing does take up less room. These are just a few factors to consider. Framing the exterior walls of a home is an excellent way to proceed. Interestingly, most homes that I design are masonry because most folks tend to feel more comfortable with masonry walls. There is a perception of additional strength. But, frankly, the facts indicate that this is a false sense. If done properly (and it is important that it be done correctly) framing is a better value.