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Plywood vs. OSB
When plywood was developed to replace solid-board sheathing for subfloors and decking, builders were generally reluctant to switch to the new product, which ultimately became the standard for subfloor applications. When OSB came on the scene as an alternative to plywood, detractors were quick to point out its deficiencies. The truth is that plywood and OSB each have strengths and weaknesses when used as exposed decking or subflooring.
When a roofless, partially built structure takes on water, both plywood and oriented strand board (OSB) used for floor decking can absorb water, swell, delaminate, and require sanding or replacement before finish flooring can be installed. The fix is to use water-repellent or water-resistant products in place of ordinary plywood or OSB.
Plywood and OSB are considered “structural panels,” and building codes treat both materials equally. Compositionally they are different, however. Plywood is made from glued strips of wood veneer that are layered at alternating 90 degree angles and placed in a hot press. The resulting cross-laminated and layered material is structurally enhanced and resistant to the expansion and contraction that affects wood.
OSB uses 3-inch to 4-inch strands of wood that are also layered and configured in a crossing pattern, then glued and pressed. OSB is heavier than plywood, absorbs less moisture, and is considered a more structurally consistent product. Furthermore, OSB does not have the delamination issues that can plague plywood. However, OSB is prone to edge swelling when exposed to moisture, and does not dry out as fast as plywood. In addition, a couple of national ceramic tile associations have discouraged the use of OSB as a subfloor or underlayment below a tile or ceramic finished floor, due to the problems encountered by edge swelling. “Wood and water just do not mix well,” says Jeff Key, marketing manager for wood products at Georgia-Pacific. To address these water issues, OSB and plywood manufacturers are refining their products.
Products like AdvanTech, an OSB product by Huber Engineered Woods, were brought onto the scene to meet the need for moisture-resistant OSB. Essentially an enhanced OSB material, AdvanTech uses a resin integrated with the wood to resist water absorption and reduce the swelling that plagued the original OSB subflooring. Huber even offers a 50-year warranty on AdvanTech.
Using a water-resistant subfloor product saves the builder time and money because they make compromised deck sections a thing of the past. “I use the AdvanTech sheets so I don’t have to worry about sanding the edges later,” says James Langeway, a Vermont contractor. Louisiana-Pacific offers Top-Notch, an enhanced subflooring system with an edge coating to prevent water absorption and a self-draining notch design that drains standing water away from the panels.
Acknowledging that some builders are going to be loyal to plywood, Georgia-Pacific recently went national with its new line of enhanced plywood, called Plytanium DryPly. DryPly is plywood treated with a water-resistant coating. “Our product comes with a 100 percent builder satisfaction guarantee against delamination, edge swelling, and joint sanding,” says Key. By combatting moisture issues, this new generation of plywood aims to go head-to-head with the enhanced OSB products. “There really isn’t another plywood product out there like it,” adds Key.
This evolved plywood may claim an overall advantage over OSB, since plywood is a stiffer, longer-lasting subfloor option. It will also hold up better under flooring accidents like leaks or flooding, and has greater nail withdrawal strength to hold the nail in under stress. “The difference with plywood is not felt initially during the first walk-through by the owners,” says Key. “It is made for long-term durability.” This sentiment is backed by Georgia-Pacific’s lifetime warranty on the product.
The cost of any wood product will fluctuate by region and supply. OSB is generally less-expensive than plywood, which is why a good number of high-volume builders have turned to it. The cost of plywood will vary depending on wood species, a factor that can also affect performance. Enhanced building products will cost more, but the savings come in time and materials when a second subfloor is not needed and finish flooring can be installed directly on top.