Oriented Strand Board or Plywood

The price of solid timber keeps rising, while environmentalists tell us to use every scrap of tree we harvest. Plywood and oriented strand board (OSB) can help us achieve this goal, although both have their limitations.

We discuss these two materials, and explain how they work. That’s because we believe in customers making informed decisions, as opposed to blindly following advice from contractors who may have a surplus of one or the 0ther material.

What is Plywood?

Plywood comprises successive thin layers of solid wood glued together, with their grains offset up to 90 degrees each time. This rotation reduces the possibility of nails splitting the edges, and encourages consistent strength and stability.

There are different types of plywood for various applications. Softwood plywood is easier to work with, while hardwood is more impact-resistant. Decorative plywood is more expensive, because it comes from rare timber. Finally, flexible plywood has thinner inner layers to facilitate bending into decorative shapes.

What is Oriented Strand Board?

Oriented strand board is a type of particle board in which wood flakes are mixed with adhesive, and then compressed so they lie in a particular direction. Its favorable mechanical properties render it suitable as load-bearing material in construction. There are five grades to choose from:

OSB/0 – contains no added volatile formaldehyde resin.
OSB/1 – general purpose boards for interior dry conditions
OSB/2 – load-bearing boards for dry conditions only.
OSB/3 – load-bearing boards suitable for humid conditions.
OSB/4 – heavy-duty load-bearing boards for humid conditions.

Oriented Strand Board (Elke Wetzig BY CC 3.0 Share Alike)

Which Is Best: Oriented Strand Board or Plywood?

Both types of boards find uses on roofs, walls and floors. But this depends on the conditions and the particular application too.

Humid Conditions

Both types of board may work well in humid conditions, but there are limitations. OSB is more moisture resistant, but it takes longer to dry out. Moreover, extended damp periods may cause the edges to swell. It is particularly important to keep it covered during installation.

Plywood has almost the opposite characteristics. It becomes wet faster, but dries out sooner. However, it can deteriorate if left damp for a long time. It should cope well during assembly. That said, the material is unsuitable for exposed exterior use.

Structural Considerations

Plywood sheeting, and suitably-graded oriented strand board have comparable strengths when used correctly. Once again, we recommend keeping both dry when exposed to the air. Because moisture damage can cause them to swell and buckle, robbing them of tensile strength. Contact Valiant Exteriors for more advice on local Calgary conditions.