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Oriented Strand board (OSB)

By HHI Staff

Oriented Strand Board (OSB) is a wood-composite used in both residential and commercial building. OSB is often used in place of plywood for construction of walls, roofing and floors. OSB, like plywood, is made from wood material held together by resins and glue. Unlike plywood, which is made from thin sheets of shaved wood, OSB consists of flakes or strands of wood produced by the grinding or shredding of whole logs. OSB is more efficiently produced than plywood, and the end product is less expensive, as well as more consistent and uniform.


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OSB and plywood are structurally equivalent in many ways, and each has pluses and minuses depending on specific uses and environmental factors. OSB does not hold up as well as plywood when exposed to moisture. Subject to wetness, plywood will readily soak in water or moisture, but will dry very fast once conditions change. OSB, on the other hand, absorbs moisture more slowly but once wet is likely to stay that way. OSB also has a tendency to curl or warp around its edges, which can sometimes be seen in roofs constructed with OSB.

Mold infesting wet or damp OSB materials is a potential health hazard. Once covered by siding, shingles or flooring materials, OSB contaminated with mold becomes a hidden problem that is likely to get worse over time.  Mold contamination can cause a variety of health problems; common symptoms of mold exposure include an irritated or scratchy throat, running nose, sinus congestion and infections, breathing problems, itchy eyes, fatigue and a general malaise.

Another health concern is the potential for offgassing of chemicals used in manufacturing. OSB and exterior plywood both contain a formaldehyde-based, waterproof resin called phenol-formaldehyde (PF). Compared to the widely used urea-formaldehyde (UF) resin, PF resins emit relatively low levels of formaldehyde. UF resins, which are found in composite materials used in cabinets, shelving, paneling and other products, are more toxic and outgas significantly more formaldehyde than PF-based glues.

Avoid or minimize problems with OSB by:

  • Inspecting OSB panels to be used for construction or home remodeling for signs of water-damage or mold. If you suspect it may be damaged, calling in a professional inspector may be warranted to avoid structural and health-related issues down the road.
  • Not using OSB for subflooring, particularly in bathrooms or other areas where moisture and exposure to water is likely.
  • Avoiding materials made with formaldehyde. Research manufacturers for those making formaldehyde-free OSB.  
  • Isolating it from the living space. As with construction-grade plywood, it can often be used in a healthy house if it is well-separated from living areas.


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Oriented Strand board (OSB):  Created on December 25th, 2009.  Last Modified on January 7th, 2010


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