Oriented Strand Board (OSB) has gained popularity very rapidly for being environmental-friendly. Almost 70% of the sheathing is done by OSB for its durability which is similar and cheaper as plywood.
OSBs lack formaldehyde and they are absolutely non-toxic to the environment. Moreover, this engineered board is made from chips of fast-growing trees like aspen, and the chips are put in layers before compressing hard and forming a board.
The vacant areas are filled using wax, making these boards water-resistant and with a bit more customizing, they might be waterproof, as well.
They are not aesthetically pleasing to the eye but due to their durability and cheaper price, they have claimed fame, and are used for sheathing walls, roofs, and floors.
The reason for the popularity of OSB is that they are water-resistant, structurally consistent and available almost everywhere in North America, take long to get wet, and are cheaper than any other sheathing.
Now, let us know exactly how thick should OSB sheathing be and learn more interesting facts about OSB.
OSB sheathing thickness
The thickness of the OSB (Oriented Strand Board) sheathing depends on the area or surface on which it is being installed or will be. Typically, the roof needs a thickness of half inches, floors need ¾ inches, while walls need ⅜ inches or 7/16 inches–if the exceptions are overlooked.
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The popularity of OSB has been recent in making and yet almost every house in North America prefers to use OSB sheathing as exterior and interior walls, including roofs and floors.
Exterior OSB sheathing:
Almost 70% of all the houses in all over North America contains OSB as sheathing in the outdoors. This is because OSB is more water-resistant than any other kind of sheathing.
These water-resistant characteristics come from the use of waterproof resin adhesives used in every layer of the board.
OSB absorbs water slower and remains dry due to the use of resin as adhesive, use of wax to bond the chips of wood. And, with more configurations, these boards can be made waterproof even.
However, once the OSB absorbs too much moisture, it swells and deforms, creating bubbles on them, and has to be replaced.
Interior OSB sheathing:
OSBs are even used as floors these days, and surprisingly, people prefer it over plywood.
That is because, OSB is more structurally consistent and dense than plywood, is way cheaper than plywood, more water-resistant, and more available and preferred by builders.
But, when the boards get dry after being wet, their edges swell and that creates an unseemly scene, and for this reason, has been discouraged to be used as flooring and as an underlayment.
Roof OSB sheathing:
OSB is strong, durable, and water-resistant. This means it can make a good, durable roof sheathing for the roofs, and protect the roof.
Moreover, they are cheap and come in various thicknesses and the thickness is even all over the boards.
However, since OSB takes a long to get wet, it takes longer to get dry as well and this tendency to hold moisture for a longer period of time says negative about OSB’s durability and it tends to degrade.
Wall OSB sheathing:
OSB can definitely be used as an interior since they are cheap, durable, and good for structural support.
Their dense structure helps in sound-proofing rooms, as well. In some cases, they provide a chic aesthetic, and some even consider leaving the board unpainted.
On top of that, these boards meet the air and vapor permeance specifications that need to be met for normal living in a house without suffocating, or the room being too humid or too cold.
1/2″ OSB vs 7/16″ OSB for wall sheathing?
Majority area-wise, the use of a 7/16 inches OSB sheathing is preferable for wall.
The thickness of the sheathing depends on the area where one lives and the span between the rafters/trusses.
In most cases, a 7/16 inches OSB wall sheathing is used since they are more available while the ½ inches is not widely found, maybe not even in the lumber yard. Therefore, in a sense, the 7/16 inches OSB wall sheathing is preferable.
However, when one is sheathing the whole wall, the thickness rarely matters since most importance of sheathing is taken by the roof and it is used on walls, by popular opinions, only for the purpose of maintaining the aesthetic beauty.
The extra thickness that comes with using the ½ inches sheathing, doesn’t really make a big difference, only costs more than a 7/16 inches thick OSB wall sheathing.
What is the code for OSB sheathing thickness?
There are no specific codes for the thickness of an OSB sheathing since it’s mostly governed by the distance between rafters, weather, and the place of installation.
Even then, a typical measurement’s followed by the constructors and realtors and they are elaborated below.
For Walls:
The thickness of walls depends on the weather and the material and position of the wall and sheathing.
If the wall of the house has stucco installed, or if it’s built in a place that’s particularly prone to natural calamities or harsh weather, the sheathing should be a bit thicker, preferably ½ inches.
Otherwise, the optimum thickness for OSB sheathing is 7/16 inches.
For Floors:
The thickness for the OSB sub-floor, the final layer on the floor which we see and walk on, is ¾ inches. OSBs aren’t known for their beauty.
Therefore if they are installed on the floor, it isn’t for beauty or humid weather since they absorb water and deform shapes rather than increase efficiency.
For Roofs:
The thickness of the OSB sheathing depends on the store and the weather. ½ inches is the typical thickness for roofs but if they aren’t adequately thick, the sheathing might sag and cause damage.
4 factors that determine OSB sheathing thickness
There are many factors that have a way of influencing the thickness of the OSB sheathing and some of them are explained below.
Rafters/ trusses:
Rafters are a series of sloped wooden structures that extend from the ridge of the roof till it meets a plate of the house and support roof.
The thickness of the OSB sheathing depends highly on the span between two consecutive rafters. According to the specific distance between two rafters, the thickness of the board is chosen.
Weather:
In some areas, the weather is more harsh as that has the ability to make the shingle of the house look dilapidated.
In some areas, we have heavy rain or snow, on top of strong thunder and tornadoes that can create huge damage if the house is not fortified enough.
A roof or wall keeps you safe from harsh weather.
Heavy snow might result in the shingle sagging and creating an unseemly look, and might also break and fall, whereas, in walls, the walls might be less protected if the OSB sheathing is not adequately thick.
Living Area:
There are certain requirements when it comes to installing sheathing, and some of them are weather, local codes, local lumber yard, and so on.
Where one leaves, the constructor and realtors will always use a specific thickness, which then depends on the area on which the house is being built.
Some lumber yards do not contain the products that are necessary or the ones we need.
There is also the factor of weather. In some areas, the rain or snow is so heavy, that it affects the thickness of the sheathing.
Place of installation:
The thickness of an OSB sheathing depends on the place where it is being installed. The roofs are normally made the thickest due to weather. The walls are built a bit thinner than the roof unless the wall has stucco.
The thickness differs because the roof takes for the brunt of the weather than the walls or floors.
Is OSB or plywood better for sheathing?
Based on popular opinion, plywood is better for sheathing since it is more durable even though OSB is cheaper.
There are advantages and disadvantages to both types of sheathing but both of them are almost equal when it comes to durability and functionality.
Plywood are stronger than OSB, and they have the ability to absorb moisture quicker as well as dry quicker. While both the sheathing has the tendency to absorb moisture and swell when wet, plywood dries faster while OSB doesn’t, leaving it to deform.
The quicker the sheathing dries, the more durable it is, and plywood takes the lead here. But, OSB being cheaper, these are used more often in homes for sheathing the walls and roofs.
Final Thoughts
The area or surface on which the OSB (Oriented Strand Board) sheathing will be put or placed determines how thick it should be. Typically, the walls need to be 3/8 inches or 7/16 inches thick, the floors need to be 3/4 inches thick, and the roof has to be half an inch thick.