What Is OSB Flooring?OSB stands for oriented strand board. OSB has the appearance of giant cornflakes pressed together to form structural panels in sizes similar to plywood, such as 4' x 8' x 5/8". Because OSB is unattractive on its own and would never serve as a finish floor, it is more accurate to say that there is really no such thing as OSB flooring. OSB subfloor is more accurate because it serves as a base under the finish floor (hardwood, engineered wood, vinyl tile, etc.) and even underneath the underlayment, in some cases.
Bones of Contention About OSBContractors, builders, and home remodelers have mixed opinions about the use of OSB for flooring, mostly tending toward the negative:
- Moisture Resistance - When OSB flooring is left exposed to the weather, unsealed edges have a tendency to swell and bubble up. This requires contractors to sand down those "bubbled up" areas after the house has been buttoned up and before the finish flooring is installed.
- Adhesion - OSB's materials are held together with resin binders and wax. The wax makes it difficult, if not impossible, to adhere some types of flooring directly to the OSB subfloor, requiring the installation of a plywood or cementboard underlayment.
- Weight - OSB is heavier than plywood.
- Drying Ability - Once wet, OSB stays wet for a long time--slowing down the project.
- Poor Wood - Base materials for making OSB--poplar, aspen, etc.--are very rot-prone woods. This means that the resin and wax additives "pull the weight" of keeping the material from rotting away.
- Nail Withdrawal - Nails pull out more readily from OSB than plywood. Not a favorable quality when nailing down flooring.
Why Some Contractors Like OSB For FlooringA few builders say that they prefer OSB over plywood for flooring because the surface (when new) is always clean, flat, and knot-free.
Simply put, many contractors find OSB to be a more consistent product than plywood or other types of material for subfloor: every sheet is the same.
The other motivation for builders to use OSB is money. OSB tends to be less expensive than plywood, so builders and contractors can squeeze a bit more profit out of the project. When OSB goes beyond flooring use and into wall and roof sheathing, the profit margin increases.
A Few OSB Flooring Myths DebunkedIs there anything to be said in favor of OSB for subflooring? It is helpful to debunk a few myths about OSB.
Myth: OSB is made from waste products.
Truth: No. Trees are logged expressly for the manufacture of OSB. No bark is used.
Myth: OSB and plywood are vastly different in term of construction.
Truth: Not really. Both products are "sandwiches" of many layers of perpendicularly-grained wood. The main difference is that OSB mats, as they are called, are composed of smaller segments of wood than are plywood layers.
Myth: Plywood is stronger than OSB.
Truth: Yes and no. For flooring applications, this is most likely true. OSB has excellent shear strength; that's why OSB is used for wooden I-beam joists. Yet shear is not an issue with flooring. OSB deflects more than plywood, which is a big reason why tile contractors unequivocally say that OSB should not be used under tile. OSB deflects 10% more than plywood under foot.
Myth: OSB is responsible for thinning out our forests and is not considered "green."
Truth: OSB uses smaller-diameter, faster-growing wood such as aspen poplar, southern yellow pine, and mixed hardwoods. In some instances, the waste bark is used as an energy source in the manufacture of OSB.
Myth: OSB instantly falls apart when it comes in contact with moisture.
Truth: It is true that OSB isn't as good against moisture as other materials. Yet the resin binders and wax in OSB help it perform adequately well in light water conditions.
Summary: OSB Flooring - Yes or No?As foreclosures mounted in 2008-11 and housing "starts" became non-starters, OSB became the visible face of failure. Under all of that flapping, wind-torn Tyvek was OSB swelling up, bubbling, flaking away, and looking like dried-up salt flats.
So, that is the public relations failure of OSB. But OSB supporters say that OSB properly installed and maintained is just as good as anything else.
If you are a homeowner building your own workshop or laying own your own subfloor in your house, pay the extra money and buy the 5/8" CDX plywood.
If you are a contractor or builder, plywood or OSB. If cost is an issue and you can ensure a moisture-free environment, you may want to consider OSB.