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What is Oriented Strand Board?

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  • Written By: B. Turner
  • Edited By: W. Everett
  • Last Modified Date: 24 August 2016
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Oriented strand board, or OSB, is a type of lumber that shares many properties with plywood or fiberboard. While other types of wood sheeting typically feature a smooth surface, this type features a rough surface made up of hundreds of wood chips. While these scraps of wood may appear randomly placed, each piece of wood is actually aligned to maximize the strength of the panel. Manufacturers combine multiple layers of these wood chips to create a board up to 1 inch (2.54 cm) thick. The layers are then subjected to high levels of heat and pressure and joined together with resin to create a secure bond.

Builders use oriented strand board to construct wood-framed homes and commercial buildings. These boards serve as sheathing to support lumber framed walls and roofs, and also serve as a base for interior or exterior finishes. For example, builders may fasten siding or roof tiles to the boards, or even apply stucco or plaster over the surface of the OSB. When installed over top of floor joists, this type of material can also serve as a support base for flooring.

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OSB comes in a number of varieties to suit the needs of different applications. For interior applications, installers rely on interior grade products, which are designed for areas with little to no moisture exposure. Exterior grade oriented strand board can be used in areas subject to minimal amounts of moisture or humidity changes, while moisture-resistant products must be used in wet areas.

One of the primary advantages of using this material is its low cost compared to plywood or fiberboard. While most experts agree that plywood and oriented strand board share virtually the same properties in terms of strength and durability, OSB is less expensive, which can reduce overall building costs. Oriented strand board also offers a more uniform and consistent construction, resulting in greater stability. Because it consists primarily of wood scraps, OSB is also considered more eco-friendly than plywood.

Excess moisture can lead to big problems with OSB, particularly if the boards are not sealed properly. While OSB generally gets sealed during production, field cutting results in unsealed edges that allow moisture to seep in. Once it gets wet, OSB tends to swell or warp, resulting in poor performance. Wet oriented strand board may even telegraph through floor or wall finishes. To prevent these types of problems, installers must reseal any edges cut during construction to minimize the risk of moisture exposure.

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Discuss this Article

kentuckycat
Post 4

@titans62 - When I was in college, I actually worked in a wood products lab on campus where forest products researchers got grants from the different lumber companies to design and test new products. I really learned a lot about how everything happens.

OSB is usually make from aspen and poplar trees, whereas plywood is usually pine or Douglas-fir. Aspen and poplar are cheaper to grow and can have the same strength as pine when they are chipped. The pattern OSB uses depends on the size of the board, but in general the layers are at 90 degrees to each other with a few randomly oriented layers thrown in the middle.

There are a lot of different things being tested at the moment. When I was working there, we were seeing how we could reuse the waste material from cotton production to make boards.

titans62
Post 3

When they are making OSB boards in the factories, how do get the special arrangement of the wood chips that the article mentions? There is no way that they have people individually setting the different chips. Along the same lines, what is the specially arrangement that results in the best strength?

Also, what are the differences in oriented strand board vs plywood? Do they both use pine wood, or are there different types of wood that get used?

I have painted plywood before with no problems. Can you also paid OSB fairly easily (besides the fact that the surface isn't smooth)?

Emilski
Post 2

@stl156 - Like the article mentions, and you have found out with the shed, if it gets wet it can start to fall apart a lot easier than plywood can. I can't recall if I have ever seen any treated OSB at my lumber yard or not. They don't always carry the widest range of stuff, though. I would just call the places around you that sell wood and see what they tell you.

If all else fails, you might be able to use some sort of a polyurethane sealant or something similar. By that time, though, it might have just been cheaper to get the plywood.

You question got me wondering, though, how resistant OSB was to termite

damage. When I had part of my siding redone, I'm pretty sure they used OSB. We have never had any problems with termites before, I am just curious if they would be able to chew through OSB faster than plywood or whether the resins help resist termites.
stl156
Post 1

I had no idea you were supposed to reseal the edges of OSB after you cut it. I didn't know it was specially sealed. I just figured it was like plywood, and you could use it how it was. Maybe that would explain why when I used OSB for the floor of my shed it didn't last as long as I expected it would. Now I know, I suppose.

I have only used OSB in dry situations, but is it possible to buy OSB that has been weather treated? I would like to use some of it for an outside project instead of plywood, but I'm not sure how it would hold up. Any advise?

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