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Plywood was once the industry standard. However, in recent years, OSB has gained impressive popularity. The two share a lot of similarities, but they both have their advantages and disadvantages.
Which is stronger? Which one should you be using?
How They Are Made
First, it’s important to understand how plywood and OSB board is made. Both are created from small pieces of wood, which are combined to create large sheets.
Plywood starts with thin strips of wood, known as plies. They are laid in layers at 90 degree angles to each other. Then, with the help of glue and a hot press, they are made into sheets.
OSB stands for Oriented Strand Board. It uses smaller strands, about 3-4 inches. They are placed in layers in a crossing pattern, and then glued.
Plywood requires mature trees, while OSB can be made from smaller trees.
Which is Stronger?
This should be a simple question, with a simple answer, right? In reality, it’s not. Which is stronger depends on the situation.
Shear Strength
We’ll start with shear strength. This is how much pressure it takes to break a board. OSB is 2 times stronger than plywood in shear values. However, this is far from the end of the debate about which is truly stronger.
Screw and Nail Holding Ability
For many applications, the strength of the board itself is only half the story. Once fastened to a structure, the board is only as strong as the screw or nail that is holding it.
If enough force occurs, the screw or nail can be removed, causing the board to fail.
APA testing found that plywood held screws better than OSB. 5/8 plywood had a withdrawal strength of 79.7, while 23/32″ OSB had an average withdrawal of 67.6.
Florida Controversy
When considering the strength of plywood vs. OSB, it’s important to take a look at Florida. After Hurricane Andrew, Florida determined that OSB was an inferior material for roofing.
After Andrew, Florida created an advisory committee to determine how such disasters could be reduced in the future. One of the committee members was Jose Mitrani. He is also a civil engineer and professor at Florida International University.
Mitrani noticed something when combing the debris after Andrew. He saw a lot of shattered OSB, and very little broken plywood. Mitrani’s eventual conclusion was that OSB swells when it’s wet. This allows the nails to come free with less force than is required for plywood.
He noted that the APA’s tests, and his own data, shows that OSB is strong or even stronger than plywood when dry. However, he didn’t agree with the APA’s assertion that this also applied to wet OSB.
The APA had their own theory. They claimed it was improper building, and improper inspections as well. A senior APA engineer notes that he saw many construction issues, including too few nails, among the debris.
As of 2022, both are acceptable for roofing, except in two Florida counties. These two counties don’t allow OSB for roofing, so plywood must be used.
Impact Strength
However, it’s not Andrew that led to this restriction in Dade and Broward counties. It’s a missile test. The test fires a 9 pound 2×4 at 34 mph. To withstand the impact, plywood must be 19/32 inch. OSB would need to be 30% thicker to meet this requirement.
This would make it infeasible as a construction material, even if it was allowed.
Whether this level of strength is necessary, or simply arbitrary, is up for debate. Homes do undergo impacts during severe weather events, and items dropped onto floors can also cause an impact. Impact strength is important, but how much impact strength should be required is less clear.
However, when it comes to impact tests, plywood is stronger than OSB.
Summing Up Plywood vs. OSB Strength
It’s important to know that both plywood and OSB meet the same building requirements in nearly all areas, and perform similarly in most tests.
OSB has a greater shear strength. However, when nails or screws are used, plywood performs better than OSB. When it comes to impact strength, plywood is the clear winner.
Choosing Between Plywood and OSB
How do you determine which is better for your project? Both plywood and OSB have their own strengths and weaknesses. You’ll find people who are zealous about using one or the other quite often. This seems to be influenced by the area they work in, as well as their personal experience with the products.
To understand which is truly better for you, let’s take an objective view of the pros and cons of each.
OSB is More Consistent
OSB’s manufacturing process makes it more consistent than that of plywood. Plywood can have what’s known as soft spots. This is because knots and other imperfections can be placed on top of each other.
OSB has more layers, which provides more consistency. OSB is also denser and heavier than plywood, which also lends more consistency.
Moisture Considerations
Plywood absorbs moisture faster than OSB. However, once plywood dries, it maintains its shape and structural integrity. It also dries much faster than OSB.
Both plywood and OSB will swell at the edges, but OSB will remain that way even after the board is completely dry. This can cause problems, particularly when OSB is used as a subfloor. A few ceramic tile associations have recommended against using OSB subfloor for this reason, at least if installing a tile floor.
Cost
Cost is far from the only consideration when choosing building materials, but it is important. Prices vary based on the type of plywood or OSB and the region.
However, OSB is nearly always significantly cheaper than plywood. This is a big reason for it’s surge in popularity in recent years, particularly among multi-family home contractors.
Weight
OSB is heavier than plywood. Exactly how much varies depending on the type of plywood and OSB. The biggest impact this has is during construction. OSB is heavier, which makes it a bit harder to handle.
However, the extra weight may have other implications as well. It requires the structure to hold more weight,which can eventually put more strain on the structure.
Size
Plywood is available in a few standard sizes, usually 8 ft or 10 feet. However, OSB can be purchased in lengths up to 16 feet. This can be particularly helpful for walls. You can install floor to ceiling sheets, avoiding having a middle seam.
Durability
Plywood and OSB are thought to perform the same in terms of sdurability, assuming that high moisture exposure isn’t an issue. Moisture can cause OSB to degrade faster than plywood, because it holds moisture longer.
Plywood has been around for more than 50 years, so it has a clear track record for durability. OSB is the newer material, arriving on the scene about 30 years ago.
So, it’s impossible to say for sure if OSB holds up as long as plywood over an extended period of time at this point.
Appearance
If appearance matters, you’ll want to choose plywood. Some types of plywood have a smooth surface that can be painted or stained. OSB doesn’t have this, and is only used in applications where it will not be visible.
This means it can be used in roofing, subfloor, and wall sheathing, but not finishing applications like cabinets or flooring.
Best of Both Worlds?
You may find that plywood is better for some applications, while OSB is suitable for others. OSB works well for wall sheathing, and potentially for roofing. Keep in mind, however, that plywood fares better in impact tests.
Plywood is considered better for subflooring, because it is stiffer and holds its shape.
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