The best plywood for installing under flooring may not be plywood at all. When used as flooring sub-floor or underlayment, OSB runs neck-and-neck with plywood, according to the opinion of contractors, tradespeople, and other industry influencers.
Contractors tend to give higher marks to plywood than OSB, not just regarding flooring but with sheathing and roofing. Georgia-Pacific, the manufacturer of both OSB and plywood, recommends plywood for flooring. Installers find OSB slightly more difficult to work with than plywood since OSB is heavier and more prone to breakage than plywood.
Plywood and OSB Defined
- Plywood: Most people are familiar with the general nature of the plywood. But homeowners who do not work with plywood much may not know that plywood's great structural strength can partially be attributed to its perpendicular layers of veneer. These veneers are laid back and forth and glued together until a cohesive "sandwich" is formed.
- OSB: Oriented-strand board looks like large flakes of wood compacted together into a sheet. That is exactly what it is: about 50 layers of these "flakes" arranged roughly perpendicularly and sealed together with phenolic resins to make a single sheet.
Look for plywood that is graded "AC." This designates a product that is graded as "A" (smooth and sanded) on one side with the other side-graded "C" (rough, knotty). You will place the "C" side down.
Plywood that is ship-lapped or tongue-and-grooved means that its joints will mate with each other, ensuring a cleaner seam between the boards.
Compared to plywood, OSB is a relatively new building product. A leading manufacturer of both plywood and OSB, Georgia-Pacific, has been making plywood since 1964, but OSB only since 1982.
How do plywood and OSB stack up in major categories? In each category, the favored product is listed first.
Plywood: Across equally spaced joists, plywood can be up to 10 percent stiffer than OSB.
OSB: Smooth sub-floors rarely matter with solid floorings like hardwood or engineered wood. But they do matter when laying floor coverings that can "telegraph" imperfections from below—vinyl, laminate, and linoleum. AC plywood is comparable to OSB wood on its "A" side. OSB will be smooth on either side, making this a product with slightly greater utility.
OSB: OSB is $3 to $4 less per panel. If you are doing a whole-house floor installation, this cost difference can add up.
Plywood: OSB has waxes, which can compromise adhesion. Plywood's porous surface is excellent for adhesives.
Best Under Ceramic Tile
Plywood: Plywood works better as a substrate below tile because of its stiffness. Any flex will cause cracking in the tile's grout and even in the tile itself. In any case, tile should be installed over an underlayment of cementboard or other type of tile backer laid over the subfloor.
OSB: If huge panels are of a concern, you will find that OSB offers panels up to 8 feet by 24 feet.
Plywood: OSB's untreated, cut edges do not hold up well against moisture. Some OSB manufacturers even make a point of warranting their OSB for as long as 90 days against edge-swell. But that kind of protection against edge-swell is inherent in plywood.
Plywood: Panel-weight can be a big issue when you are remodeling by yourself. Even hoisting a mere 4 feet x 8 feet plywood panel can get tiring by the end of the day. But imagine repeatedly carrying a panel that is 15 percent heavier. OSB is slightly heavier than plywood, which can wear on you if you are handling multiple panels.
Both: OSB and plywood are covered up in flooring applications, so the appearance of the subfloor does not matter. In a pinch—if the surface had to be exposed in a workshop or shed—you could say that plywood wins out, due to its true wood grain look vs. OSB's flaky appearance.
Green and Eco-Friendly
OSB: OSB is chipped out of smaller trees and thus more productively uses timber than plywood.
Sub-flooring type— plywood or OSB—is often more of a matter of personal preference than absolute objective worth.