You want to build the highest quality home, right? Of course you do. That’s why you’re here reading this tip after you buy your home plans.

Because quality is also a concern for us, we want to help you make sure that every part of your home is as good as it can be, including hidden areas behind your walls, floor, and roof.

Many consumers are concerned when they see oriented strand board (OSB) being installed in their home. Because it costs less and looks different than plywood, they feel like they are getting a lower quality product, or that their contractor is trying to pull something on them. You need not worry; in many applications OSB has a comparable quality to plywood.

OSB AND PLYWOOD: WHAT’S THE DIFFERENCE?

Let’s start with the similarities. Building codes use the phrase “wood structural panel” to describe the use of plywood and OSB. Codes recognize these two materials as the same. They are both made by compressing and gluing small pieces of wood together.

Plywood is made from thin sheets of veneer that are peeled off a log. Picture a giant pencil sharpener. These sheets are laminated together in a hot press to make plywood.

OSB is made from wood ground into thin wood strands. These strands are mixed with wax and adhesive and then hot pressed. Approximately 50 layers of strands make one sheet of OSB.

OSB has some advantages over plywood:

  • OSB is generally more square and has smaller dimensional tolerances
  • It can be manufactured into panels of up to 8′ x 24′, far larger than plywood
  • There are no soft spots such as those that can occur in plywood
  • OSB is made from smaller (often farmed) trees reducing the demand for old growth timber
  • OSB has greater shear strength than plywood; the span rating, nail pull and screw hold are all roughly the same
  • It can be $3 to $5 a panel less expensive than plywood. For a typical 2400 square foot home, OSB will save about $700 if used as the subfloor, sheathing, and roof decking instead of plywood.

The major disadvantage of OSB is that if it gets exposed to significant amounts of water or moisture, the edges expand by up to 15%. . .especially if they are cut edges. This swell will then telegraph onto the shingles or some flooring. When plywood gets wet, it expands evenly throughout the panel, dries more quickly and shrinks down to its original size more rapidly than OSB.

The Structural Board Association has outlined a plan to prevent this phenomenon. They maintain that dry storage, proper installation, and adequate ventilation will help prevent edge swelling of OSB.

THREE COMMON APPLICATIONS

For the three main applications of OSB and plywood, flooring, wall sheathing, and roof decking, which product should I pick?

Grid marks printed on OSB and plywood will speed installation.
Photo: Martco Limited Partnership

***Whether you select OSB or plywood, use grid-marked sheathing, which includes pre-printed gridlines to facilitate measuring, marking, cutting, and fastening. It will speed installation, and save you money.***

Flooring

OSB is fine to use as a subfloor material for most types of flooring, especially resilient flooring.

If you are installing a tile floor, the National Tile Contractors Association recommends that you not use OSB as a subfloor or underlayment because of the potential that swollen edges will weaken the tiles.

Wall sheathing

OSB works just as well as plywood for sheathing. You should still check with the siding manufacturer’s installation instructions for compatibility, especially for stucco homes.

Roof Decking

Warranties on shingles are extended to both OSB and plywood, but some manufactures feel more comfortable with plywood because of the ‘roof ridges’ that can occur if OSB edges swell. OSB must be protected from rain.

ALTERNATIVES TO PLYWOOD AND OSB

Straw Board A structural strength board made from wheat and soybean straw can be used as wall sheathing. Straw boards can be more water-resistant than wood-based panels.

Recyled Paperboard Made from recycled newspapers, paperboard can be used as a sub-floor, sheathing or roof decking. Aside from being very environmentally friendly, paperboard also has a higher insulative value than wood panels and can reduce sounds. Traditionally, it is less expensive than other wood-based sheathings.

Foam Sheathing Foam insulating wall sheathings come in a variety of foam formulations including extruded polystyrene, expanded polystyrene, and polyisocyanurate. Regardless of foam type, however, foam sheathing is the most insulative of all the sheathing options. Foam sheathing does require corner bracing, as it is not structural in nature.

Gypsum Gypsum panels are used under brick veneer, and stucco finishes. An advantage of gypsum is the ability to obtain a fire-rated wall assembly. Gypsum panels, however, must be handled carefully and the paper-faced products need to be sheltered from precipitation.

Cementitious Board Cementitious board is a panel consisting of Portland cement reinforced with fiberglass mesh material. Typically used as backerboard for ceramic tile installations, cement board products have been used as exterior sheathing under a stucco cladding. Not structural in nature, buildings sheathed with cement board must have corner bracing

For more information on alternatives to OSB and plywood, read this ToolBase TechNote.

Courtesy of PATH
www.pathnet.org/homeowners