If you’re planning on renovating your roof or upgrading it to a more durable build, the first thing you need to keep in mind is the sheathing that your roof exterior will sit on. The sheathing is the foundation of your roof, and its thickness has a great impact, not only on the durability but also on the moisture resistance and noise cancellation of the roof.
The minimum requirement for roof sheathing is ⅜” thick. Plywood is slightly stronger than strand board, so ½” is the recommended thickness. However, OSB doesn’t hold fasteners as well as plywood; it must be a little thicker or at least ⅝”. Several factors determine the optimal roof sheathing thickness for added benefits like insulation.
Since roof sheathing comes in a wide variety of thicknesses, you might be quite overwhelmed by the ideal one for your house or shed, and that’s where this guide comes in handy!
In today’s article, we’ll walk you through everything you need to know about roof sheathing thickness, so you can pick the one that suits your needs.
What is Roof Sheathing?
Before diving into the juicy details of roof sheathing thickness, here’s a brief description of what roof sheathing is and what it does.
While building a roof to your house, you need a solid, flat, and smooth surface, so it acts as a base to which your roofing materials are attached.
The roof sheathing is simply this solid surface. It is added to the roof beneath the external roofing material, made of metal, shingles, or other types of roofing materials.
Back in the day, this base was known as “substrate,” a generic term that describes any supporting material used beneath the roof. The substrate used to be made of dimensional lumber or wood boards.
The problem with dimensional lumber is that it is quite expensive. Not only that, but it was also very heavy, which made it difficult to install and increased labor costs. Despite that, wood is prone to water damage and needs frequent maintenance.
Over the years, more households have replaced their old wood substrate with more affordable materials that are durable and easy to install, such as plywood and oriented strand board, which is commonly known as “OSB.”
What is the Purpose of Roof Sheathing?
The exterior roofing material provides an aesthetically pleasing appearance while acting as the first line of defense against environmental factors.
However, to fix this barrier, you need a solid and flat surface that you can attract shingles to via screws or nails.
The roof sheathing is another layer of defense designed to act as a secondary barrier to separate your interior from the exterior roofing material.
Moreover, the roof sheathing will also help keep heat and moisture out, although it’s not designed to be a moisture or vapor barrier primarily.
Instead, the underlayment over the roof deck remains the primary barrier against moisture while the attic handles the vapor.
In addition to acting as a substrate to which your exterior roofing material is attached, roof sheathing also contributes greatly to the roof’s structural durability and general sturdiness. It acts as a secondary sound barrier, which gives it a great advantage over battens.
Does Roof Sheathing Thickness Matter?
Now that you have a better idea about the roof sheathing and its importance to the roof structure, it’s easy to assume that the thickness of the sheathing plays a significant role in the quality of the build.
A roof sheathing made with a thicker panel will result in a more structurally sound roof deck.
The shear resistance of the sheathing material, coupled with the layer’s thickness, will also help resist any warping and bowing, especially between trusses and rafters.
This all will result in a more secure roof that is expected to last longer and even increases the general value of your property.
How Thick Should Roof Sheathing Be?
The minimum requirement for roof sheathing is ⅜” thick. Plywood is slightly stronger than strand board, so ½” is the recommended thickness. However, OSB doesn’t hold fasteners as well as plywood; it must be a little thicker or at least ⅝”. Several factors determine the optimal roof sheathing thickness for added benefits like insulation.
You should know about average roof sheathing thickness because it can vary depending on the material used and the level of durability you’re after.
There Is No Standard Roof Sheathing Thickness
You should keep in mind that roof sheathing thickness isn’t standardized. However, the Engineered Wood Association “APA” still standardizes the quality testing of the sheathing but not the thickness.
Instead, some standard roof sheathing thicknesses are agreed upon for being the perfect balance between durability, ease of installation, and budget.
For instance, the most commonly used thickness will be about 5/8 inch thick when it comes to strand board roof sheathing.
On the other hand, plywood roof sheathing is usually more durable, so a thinner board will still do the trick, which is why about 1/2 inch thick boards are the agreed-upon standard for plywood.
The Gaps Between the Framing Matter Too
The average roof sheathing thickness is also heavily dependent on the spacing distance between rafters or trusses.
The further your trusses or rafters are spaced, the thicker the layer of the roof sheathing needs to be.
For example, the most common spacing between trusses is about 24 inches, while the most common for rafters is about 16 inches.
Luckily, the APA regulates the maximum distance that a panel can bridge between the gaps, stamped on the roof decking in the form of two numbers divided by a slash.
For example, if a roof sheathing panel has a stamp that says 24/0. This means that the maximum gap it can hold between framing is about 24 inches.
Roof Sheathing Code Requirements
The minimum requirement for roof sheathing is ⅜” thick. Plywood is slightly stronger than strand board, so ½” is the recommended thickness. However, OSB doesn’t hold fasteners as well as plywood; it must be a little thicker or at least ⅝”.
Several factors determine the optimal roof sheathing thickness for added benefits like insulation.
What Is the Ideal Thickness of Shed Roof Sheathing?
If you’re roofing a shed, you might consider a sheathing substrate of about 5/8 inches. This thickness is considered the sweet spot at which the roof sheathing won’t cost you as much, remain easy to install and provide you with a pretty decent level of durability.
When it comes to sheathing material, you should consider OSB or plywood. These materials are excellent for the job, although OSB is preferred over plywood because it holds up better and is easier to install.
Moreover, strand board is more affordable than plywood, making it an ideal choice for those on a tight budget who don’t want to spend a lot of money on roofing a shed.
However, if you’re worried about rain penetrating your roof, plywood would be a better choice for you because it dries up much quicker than OSB and returns to its initial thickness when it dries up.
Will Cold Climates Require a Thicker Roof Sheathing?
Whether you’re sheathing a house or a shed, you should always keep the weather in mind while deciding on the suitable thickness for the roof sheathing, especially in the winter.
This is because winter is where the majority of the rain and wind occur, which are the true test of the structural integrity and durability of the roof sheathing.
Moreover, in northern states, winter is often accompanied by snow, which puts a tremendous load on the roof in terms of sturdiness and moisture resistance.
Another specification that the APA includes on the label of the roof sheathing is the maximum load it can support, which is usually measured by pounds per square foot or “psf.”
If you live in an area where snow falls regularly, it’s always better to err on the side of caution and go for a roof with a load tolerance of about 50 psf or higher.
Of course, panels rated at 50 psf or higher are usually thicker than average roof sheathing options, and they usually cost a bit more, so you have to keep that in mind.
How Thin or Thick Can a Roof Sheathing Be?
While there aren’t constant standards for how thin or thick a roof sheathing can be, we can conclude the thinnest and thickest commercial roof sheathing boards that you can find out there, whether they’re plywood strands board or other engineer wood materials.
Ideally, the thinnest roof sheathing panels on the market are usually about 3/8 inches. They usually also happen to be the cheapest on the market, especially if they’re made of strand board.
Such a thickness is suitable for sheathing a small shed in an area that is mostly dry throughout the year and doesn’t get much rain or snow.
On the other hand, the thickest roof sheathing panels will average between 1/2 and 3/4 inches. Of course, these panels are usually the most expensive, and they’re recommended for homes and sheds in areas that are struck with heavy rain and snow throughout the winter.
You should also know that sheathing thickness and span rating are not the same things. For example, you can find two panels of the same thickness and make from the same materials.
However, each of them is rated for a different span due to differences in construction, variety, and layering.
For that reason, you should look at the different specifications mentioned on the label instead of relying on the thickness alone while picking panels for your roof sheathing.
What About Metal Roof Sheathing Thickness?
There’s quite a difference between roofs that use metal for exterior roofing and others that use tiles or shingles. This is because metal roofs don’t use as many nails as asphalt shingles, so they’re held together by fewer fastening points.
For that reason, you need a solid substrate to hold the roof, which translates to relatively thicker panels with a higher span rating. Ideally, a metal roof will require a minimum of 5/8 inch panels to support the weight and design of metal roofs.
What Are the Most Popular Types of Roof Sheathing?
Roof sheathing is made of several materials. Such as:
- OSB or Strand Board
- Plywood
- Planks
- Wood boards
- Compressed wood panels
Despite that, the most popular ones on the market nowadays are OSB and Plywood, with dimensional lumber falling out of the competition because it’s significantly more costly without offering a true advantage over the much cheaper and easier to use alternatives.
OSB is currently the most popular option for roof sheathing because it’s incredibly durable, all the while being relatively affordable. About 60 to 75% of all roof sheathings in North America are currently made of OSB.
Plywood is also commonly used because it’s more durable and lighter in weight. It also dries up quicker than OSB and has a better moisture resistance in general.
What Kind of Fasteners Are Used for Roof Sheathing?
Substrates are usually fastened using either nails or screws. Since they are responsible for holding the entire thing together, it’s always critical to choose the right type of nails depending on the thickness of the boards you’re using.
Ideally, you should use 8d ring shank nails that are specifically designed for roofing. These nails are about 2.5 inches long, making them long enough to fasten just about any roof substrate regardless of its material or how thick it is.
As for screws, the size will depend more on the thickness of the panels. For example, if you’re getting a panel that is 1/2 inch thick or less, a #10 roofing screws would do the trick because it’s about 3 times longer than the board.
If you’re opting for a thicker roof substrate, you can go for #12 roofing screws, which are about 2 inches long.
Lastly, you should never try to fix your roof sheathing with staples, as they’re never durable enough to hold up the roof properly.
Roof Sheathing Thickness FAQs
What Thickness OSB for Roof?
How Thick should Roof Decking Be?
The typical roof decking thickness is ⅜” thick. Plywood is slightly stronger than strand board, so ½” is the recommended thickness. However, OSB doesn’t hold fasteners as well as plywood; it must be a little thicker or at least ⅝”. Several factors determine the optimal roof sheathing thickness for added benefits like insulation.
What Size Sheathing for Roof?
The recommended size sheathing for roofs is determined by the spacing of the rafters. Some experts suggest that 19/32-inch plywood should be the minimum if the underlying roof rafters are spaced 16 inches apart or less, but you should use slightly thicker 3/4-inch plywood for rafters further apart.
Wrap Up
With that said, you now have a brief guide with everything you need to know about roof sheathing thickness and how to choose the ideal one for your needs.
Typically, most roof sheathing panels on the market will range from as thin as 3/8 inches up to 3/4 inches, with 5/8 inches being the most commonly used thickness because it’s an excellent balance between durability, price, and ease of installation.
Remember to also check the label on the panel you’re about to buy and make sure that other specifications are also suitable for your condition, such as the maximum psf and span rating.