Roofing systems are like onions—they come in layers. Alongside the primary surface material, they consist of shingles, flashing, underlayment, and sheathings.
This article focuses on the layer fixed to the roof’s joists and trusses: the sheathing.
The roof sheathing plays a vital role in the roofing system. It adds insulation and a radiant barrier and increases the strength and rigidity of the roof. Moreover, it evenly distributes the weight across the house’s top structure.
This layer comes in two materials: Plywood and OSB. Both materials come with their advantages and disadvantages. We’re going to discuss that and more in today’s article.
OSB vs. Plywood for roofing: which is the right material for you? Let’s find out.
What Is OSB?
OSB, also known as Oriented Strand Board, is manufactured wood made out of compressed layers of wood strands and bonded together with adhesives like synthetic resin and wax. All in all, it’s 95% wood and 5% wax and/or resin.
Due to its high strength, it’s especially suitable for load-bearing applications in construction. Although considered a low-cost alternative to plywood sheathing, OSB has better structural integrity and is more readily available.
To date, OSB is used on 70% of floor, wall, and roof sheathing in North America.
OSB is produced in a variety of types and thicknesses. Some of the most common types of OSB are OSB1, OSB2, OSB3, and OSB4.
OSB1 (Type 1) is nonstructural and non-waterproof, which is why it’s rarely used in roofing applications. OSB2 (Type 2) is ideal for structural, non-load-bearing conditions. Although it’s water-resistant, it’s best used in areas that experience little rain or snow.
OSB3 and OSB4 (Type 3 and 4) are both suited for roofing applications, as they perform very well in structural, load-bearing conditions and harsh weather. Additionally, they’re bonded with phenol-formaldehyde resin (PF), increasing their moisture resistance and overall performance.
Is Oriented Strand Board a Viable Option for Roof Sheathing?
For any material to work as a suitable option for roofing, it must meet some essential requirements. For starters, a roof sheathing material needs to be pretty durable to withstand not only the high-speed wind of the winter but also the weight of a grown adult for any projects or maintenance.
In addition to bearing the roof’s load, it also needs to have a remarkable level of moisture resistance to prevent the rain from seeping or leaking into the house’s main foundation, causing anything from mold to structural weakness with time.
As previously discussed, OSB is made from the compression of durable types of wood like aspen and poplar. This means that with the proper thickness, such boards are capable of bearing heavy loads.
Additionally, since the flakes of the wood are mixed with a waterproof resin, it has some waterproof properties that allow it to resist varying degrees of moisture.
Based on all that, we can conclude that Oriented Strand Boards qualify as a viable roof sheathing material.
The material is so durable and strong that it’s currently used as the material for roof sheathing in anywhere between 60 to 75% of all roof sheathings and walls and floors in North America.
Not All OSB are Created Equal
Although OSB is quite strong and reliable to be used in the roof sheathing, you should know that there are two types of OSB out there, which vary in durability, insulation, and price.
These two types are known as “OSB2” and “OSB3”. OSB2 is the more affordable variant of OSB. However, it’s typically used for bearing light to medium weight loads and specifically designed for being used in mostly dry conditions.
On the other hand, OSB3 is typically used for load-bearing projects, such as roof and wall sheathing.
Moreover, OSB3 has much better insulation and waterproof rating, which allows it to be used in humid conditions. Yet, this type of board is more expensive and is used almost exclusively in structural projects.
Is OSB Approved for Use in Roof Sheathing?
Of course, the legality of using OSB in roof seething will vary depending on the local rules where you live.
According to the National Roofing Contractors Association (NRCA) and the Asphalt Roofing Manufacturers Association (ARMA), the use of OSB in roof sheathing is approved as long as it meets the requirements of the APA – Engineered Wood Association.
In other words, the use of the OSB in roof sheathing is approved by almost all authoritative bodies concerned with the structural integrity of roofs in the United States.
The only place where OSB isn’t approved for roof sheathing in the U.S. is in Dade County, Florida.
OSB was approved for use there until 1992 when Hurricane Andrew caused significant damage to the area’s rooftops.
After the devastating damages caused by the hurricane, the Dade country banned OSB for roof sheathing, claiming that it could not hold nails properly.
Although subsequent investigations and research have proven this claim false, the country maintains its ban on OSB.
In addition to the U.S., Canada also approves the use of OSB for roof sheathing as long as the panels meet the Canadian Standards Association requirements, which are based on the CSA O86 Engineering Design in Wood and CSA O325 Construction Sheathing.
Advantages of OSB Roof Sheating?
Now that you know more about OSB and that they’re approved for roof sheathing in most of North America, here are some of the most significant reasons why you’d want to use this material while sheathing your roof:
1. Excellent Level of Sturdiness and Dimensional Tolerance
OSB is made from durable strains of wood, which makes it a naturally durable engineered wood.
Additionally, the way these layers of wood are compressed also adds to the shear strength and sturdiness it has.
The design of the panels made them more square with an adequate dimensional tolerance, which exponentially boosts the ability of OSB to support heavy load projects like roofing. This explains why OSB is becoming the most popular material for roof sheathing, ahead of plywood, planks, and other compressed wood panels.
2. Highly Affordable When Compared to Other Options
Another significant reason why many homeowners are opting for OSB while sheathing the roof is how inexpensive it can be.
For instance, a 4 x 8 ft sheet of OSB will cost you anywhere between $4 to $7, while other materials, such as plywood, would cost you about $10 for the same size sheet.
Since they cost about the same to install, which is usually around $70 an hour for a professional carpenter, going with OSB can save you a lot of money.
Despite that, you won’t compromise the quality, as both materials have the same screw hold, nail pull, and span rating, with minor differences in general durability.
3. Consistent Design
Another advantage that the OSB has is that its design makes it extremely consistent and stiff across the board with a very limited range of variability.
This is because OSB can be made from up to 50 strands, evading any chances for variability or inconsistencies, making it a highly dependable roof sheathing material with little to no weak points.
4. Wide Range of Options
OSB is highly versatile and can be available in a wide range of sizes as large as 8 x 24 ft with no soft spots.
This is also an advantage that OSB possesses over plywood, as no plywood sheets are available in such size.
5. A Very Sustainable and Eco-Friendly Source
One of the reasons why OSB is affordable is because it needs young trees and doesn’t factor in the aging of the trees for the durability of the boards.
Making OSB uses up to 90% of the tree log, which is higher than many other sources.
It also doesn’t harm forests because most of the fibers for the boards are obtained from sustainable tree farms and forests.
OSB is considered more eco-friendly than plywood because it uses smaller trees and has a more energy-efficient manufacturing process.
Disadvantages of Using OSB?
Despite all its merits, some drawbacks are associated with using OSB. Here’s a quick look at these points:
1. Relatively Heavy
Since OSB may use up to 50 layers of fibers and sheets to create a single board, it’s no surprise that the boards are pretty heavy compared to other engineered wood options, such as plywood.
For example, a 23/32 OSB panel will weigh around 2.4 lbs, while a panel with the same thickness made from plywood will only weigh 2.2. This can add up pretty quickly in the case of large roofs.
While some might perceive this as an advantage rather than a disadvantage, it’ll always make the installation process a little more tedious, which calls for more workers, and therefore, more labor costs.
Additionally, the extra weight will exert extra pressure on the house’s foundation, which makes the maintenance routines slightly more frequent in the long run.
2. Has a Lower Moisture Tolerance Than Other Options
Back when OSB was first produced, it had a major problem with moisture. However, with advanced technologies and incorporating waterproof waxes in the manufacturing process, the moisture tolerance of the OSB has significantly improved.
Despite that, OSB is still slightly inferior to plywood when it comes to moisture resistance. While both plywood and OSB will swell upon exposure to moisture, plywood will return to its original thickness as it starts to dry out.
On the other hand, OSB takes much longer to dry out, which causes it to remain swollen for a significantly longer time. Even after the wood dries, OSB panels will always remain slightly swollen due to their compaction ratio.
Both OSB and plywood will be covered with water-resistant material to protect them from moisture. But, if you cut the OSB at any point, you’ll need to seal it to prevent it from swelling up on moisture and water.
3. Some Homeowners May Not Like its Look
This one is down to the personal preferences of each homeowner, although many homeowners believe plywood looks better than OSB in the roof sheathing.
What Is Plywood?
Like OSB, Plywood is often used for wall sheathing, subflooring, and roof applications. Although not as popular as OSB, it’s considered among the best types of roofing materials available.
Plywood is a type of engineered wood made from thin sheets of veneer taken from debarked wood. These sheets, also known as plies, are secured together in a cross-grain pattern at adjacent 90-degree angles. It’s then bonded with resin to form a composite material.
Cross-graining comes with several important functions. For one, it reduces the tendency of splitting wood when nailed at the edges.
Two, it balances the strength of the panel across all directions. It likewise reduces shrinkage and expansion, which therefore improves the panel’s dimensional stability and longevity.
Unlike OSB, which was first invented in 1963 by Armin Elmendorf in California, Plywood has been around for centuries, dating back to 1797. Instead, the Plywood we know and love today was first manufactured in the 1860s, where it received immediate global attention.
Plywood comes in multiple types, including softwood, hardwood, tropical, aircraft, decorative, marine, and many others. For roofing applications, softwood plywood and hardwood plywood are the most frequently used.
Pros
- Slightly stronger than OSB
- Decent moisture resistance
- Holds fasteners better
Cons
- May split in hot climates
- Uneven layers, resulting in more soft spots
- Fairly expensive
OSB vs. Plywood for Roofing: What’s the Difference?
OSB and Plywood share several structural similarities, so much so that the terms are often used interchangeably. But although they both belong in the manufactured board family, they’re two completely different materials with several distinct features.
1. Moisture Resistance
One of the most significant differences between the OSB and Plywood is their reaction to moisture over extended periods.
OSB—particularly OSB3 and OSB4—is slightly more resistant to water than Plywood. However, this doesn’t mean they’re 100% waterproof.
Thanks to its water-resistant nature, OSB sheathing takes a lot longer than Plywood to get wet. But this quality also makes it harder to dry. Plywood absorbs water quicker than its counterpart, but it also dries much faster.
Both materials swell when wet, but as Plywood dries much faster, it almost always returns to its exact shape.
OSB, on the other hand, is far less forgiving. As it doesn’t dry as fast as Plywood, it’s much more susceptible to moisture damage. When it dries, the untreated edges will appear deformed and swollen. Unfortunately, it will stay swollen even after the material has completely dried out.
That being the case, Plywood reigns on top in terms of water resistance. So if you live in an area that experiences constant rain, plywood sheathings are the better choice.
However, it’s important to remember that Plywood doesn’t hold well in extremely hot weather, as it tends to delaminate and crack.
For areas with hot weather, like Florida and Texas, consider OSB.
2. Cost
As mentioned earlier, OSB is the low-cost alternative to Plywood.
Compared to Plywood, OSB typically costs around $5 to $7 less per panel. This may not seem like much, but the cost savings are significant when used as a roofing material.
In most home improvement centers, a 23/32 in. x 4 ft. x 8 ft. OSB costs around $15, while a 3/4 in. x 4 ft. x 8 ft. plywood sells for about $22.
The installation also costs more than Plywood. Generally, OSB installation costs around $100-$110 per 500 sq ft. while plywood costs $150-$160.
If you want to replace your roof, check how much it costs to replace roof decking.
3. Structural Strength
Although OSB has better structural integrity than Plywood, Plywood is slightly stronger and more rigid. As alternating wood layers make it, Plywood offers supreme dimensional stability and strength.
For instance, a 3/4 in. x 12 in. x 36 in. Plywood can support about 50 lbs. of weight with no issues. Generally speaking, the thicker the wood, the higher its strength.
When it comes to sheer, OSB is about twice as strong as Plywood. Compared to Plywood, which has a broader range of variability, OSB is consistently stiff. Its strands, perhaps 50 strands thick, average out the “layers” found in Plywood.
Both products perform equally well in structural strength and integrity. Some may argue that OSB is slightly weaker than plywood, but the difference is so small that it barely counts.
4. Resale Value
OSB and plywood roofing don’t impact the overall value of the house unless disclosed. Both materials are attached to the roof’s trusses and joists and hidden right underneath the shingles.
Particularly observant buyers may want to pay extra on plywood for roofing, but prospects don’t often consider OSB as the “cheaper” alternative, so it won’t lessen the value of your home. Overall, sheathing material is rarely noticed.
5. Installation Method
Both materials follow the same installation technique. But since Plywood is much lighter than OSB, installing the former is easier for a home DIYer.
A single 23/32 in. x 4 ft. x 8 ft. plywood weighs approximately 67 lbs. while OSB with the exact dimensions weighs about 78 lbs.
Another minor difference is that OSB may require more fasteners than Plywood, as nails and screws are more likely to remain in place than OSB. On the other hand, plywood holds fasteners better than OSB, making it easier to install overall.
6. Care and Maintenance
Roof sheathing is hidden from plain sight, so care and maintenance aren’t essential. However, there are a few tips to consider when installing both materials.
If you’re planning to paint the OSB panel for any reason, don’t forget to apply a thick layer of oil-based primer to prevent moisture damage and swelling. Also, always use OSB3 and OSB4 panels as they’re specifically engineered for outdoor use.
In both cases, expensive repairs can be prevented by routine maintenance and regular inspections. Removing roof debris and securing or replacing loose shingle tabs maintain the integrity of the roof sheathing.
All in all, roof sheathing doesn’t require much care. Believe it or not, the roof sheathing can last as long as the house itself. Some sheathing stands strong even after 100+ years.
Plywood sheathing lasts longer than OSB sheathing because of its moisture retention. If the sheathing appears damaged, rotten, or if its fasteners are failing, it’s best to contact a professional to replace the sheathing to avoid problems in the future.
7. Environmental Impact
OSB is generally more environmentally friendly than Plywood, as it’s made from shredded wood strands. Most of these strands are obtained from smaller trees with low diameters or recycled wood from wooden furniture and the like.
However, the resins used to create OSB panels emit volatile organic compounds such as formaldehyde. Therefore, OSB that emits urea-formaldehyde is toxic and should never be used in home applications. Phenol-formaldehyde OSB is relatively hazard-free, however.
Reputable manufacturers almost always use non-toxic resin to avoid health and environmental issues. Environmentally-friendly OSB panels use isocyanate resins that, when properly cured, are nonvolatile.
On the other hand, Plywood is constructed from large frees with high diameters that take quite a while to grow, thus considered a less “greener” option.
Although primarily sourced from sustainable forests, the plywood industry carries a relatively large carbon footprint due to its high transportation and energy consumption.
The good news is that Plywood is produced without the use of chemical compounds. Instead, manufacturers use non-toxic soy-based glues to bond the layers together.
Conclusion
OSB and Plywood differ in both cost and performance. However, Plywood is generally better than OSB; it offers better moisture resistance and structural strength and looks better overall.
However, the difference in performance isn’t significant enough to disregard OSB entirely, and 70% of US homeowners seem to agree.
OSB, while cheaper than Plywood, is a perfectly acceptable sheathing material. In addition, since it’s consistently stiff, it has better structural integrity than Plywood, resulting in lesser soft spots.
With that said, OSB doesn’t fare well with moisture. Therefore, homeowners who live in areas with frequent rain would benefit from Plywood rather than OSB.
Regardless of your choice, both materials excel in their unique way. If budget isn’t an issue, it’s worth installing plywood roofing panels. Otherwise, OSB is a brilliant choice in most situations.