A good roof is not only judged by its roofing material but also the stability of its foundation. While roofing materials and underlayment are large parts in this, it also comes down to the supportive layers that hold everything else up, otherwise known as the sheathing or roof deck. But since it’s the bottom layer, most homeowners ignore it.
This structural layer is the foundation for your roofing materials, providing support and stability to ensure a long-lasting roof. The two most commonly used materials for roof decking are Oriented Strand Board (OSB) and plywood. Both options provide the same purpose, but there are also several differences between the two.
As a premier roofing company specializing in roof repair and replacement, we understand that you want to make informed decisions about roofing materials as a homeowner. That’s why we’ve created this guide to help you understand the differences between OSB and plywood sheathing. After reading, you’ll hopefully be able to determine which material is best suited for your home.
What Is Roof Sheathing?
Before diving into the differences between OSB and plywood, it’s essential to understand what roof sheathing is and why it matters. Roof sheathing is the layer of boards that covers the rafters or trusses of your roof. It serves as a base for the underlayment and shingles to be installed while distributing the weight of these materials evenly across the roof’s structure.
Quality roof decking material ensures that your roof can withstand weather elements, including wind, rain, and snow. It also contributes to your home’s overall insulation and ventilation, preventing issues like moisture buildup and heat loss.
To learn more about roof sheathing in general, you can read more here.
What Is OSB?
OSB, otherwise known as oriented strand board, is an engineered wood product made by compressing layers of wood strands (or wood chips) with adhesives under high pressure and heat. The strands are arranged in specific ways and are interweaved together to maximize the strength and durability of the deck panels. Usually, the strands are around the size of 8 to 12 cm and are mixed with resins.
Advantages of OSB:
- Cost-Effective: OSB is a cheaper option compared to plywood, which is why it’s so popular for homeowners on a budget.
- Consistent Quality: Since OSB is crafted using precise engineering methods, all panels are typically uniform in thickness and density, reducing variations in quality.
- Larger Panel Sizes: OSB panels come in larger sizes, reducing the number of seams and enhancing overall structural integrity.
- Sustainable: OSB is made from smaller, fast-growing trees, making it an environmentally friendly option that maximizes wood usage.
Disadvantages of OSB:
- Moisture Sensitivity: OSB easily absorbs water compared to plywood and also takes longer to dry, increasing the risk of swelling and weakening if exposed to weather elements for extensive periods of time.
- Heavier Weight: OSB is denser and heavier than plywood, making installation slightly harder.
- Less Breathability: Due to its compressed nature, OSB has lower permeability, meaning it doesn’t offer ventilation as well as plywood and can retain moisture if not properly ventilated.
What Is Plywood?
Plywood is a popular choice for roof decking among homeowners and contractors. Until the 1970s, plywood was the only material used for this purpose, as oriented strand board (OSB) was introduced later. Each layer, or ply, has its grain oriented in alternating directions, which improves the material’s strength, stability, and resistance to warping. This unique construction method sets plywood apart and makes it a reliable option for roofing applications.
Advantages of Plywood:
- Superior Moisture Resistance: Plywood resists moisture better than OSB, drying out faster and maintaining its shape more effectively after exposure to water.
- Lighter Weight: Plywood is generally lighter than OSB, making it easier to handle and install.
- Stronger Fastener Holding: Nails and screws grip plywood more securely, reducing the risk of fasteners loosening over time.
- Less Swelling and Warping: Plywood does not expand or contract as dramatically as OSB when exposed to temperature changes.
Disadvantages of Plywood:
- Higher Cost: Plywood is more expensive than OSB. It often uses higher-quality wood like hardwood or softwood veneers, which are more expensive to harvest and process. This can be a deciding factor for homeowners on a budget.
- Variability in Quality: Since plywood is made from natural wood layers, it can have imperfections, knots, and variations in thickness.
- Smaller Panel Sizes: Standard plywood sheets are smaller than OSB panels, leading to more seams in the roof deck.
OSB vs. Plywood: A Side-by-Side Comparison
In the above sections, we discussed the pros and cons of both OSB and regular exterior plywood sheathing. Here is a table to demonstrate those differences.
| Point Of Difference | OSB | Plywood |
| Cost | An OSB roof deck is more affordable in terms of overall cost. OSB is cheaper by 15% to 30% | Plywood is expensive due to a more extensive process and select veneers |
| Strength and Durability | OSB absorbs and retains moisture for longer | Plywood has more strength in terms of fastener retention and stability |
| Swelling | Since OSB retains moisture longer, it tends to swell more. It also requires more time to revert | Plywood does not swell as much as OSB |
| Sustainability | More eco-friendly since these are made from wood chips (smaller trees) | Less eco-friendly, requires larger trees |
Is There A Third Option?
OSB and plywood are the two most prominent choices you have when it comes to roof decking, but there is a third option. It’s not the most popular, but metal roof decks are another choice, especially if you have a commercial property.
More About Metal Roof Decks
These decks, often made from steel or aluminum, offer a highly durable and long-lasting alternative to traditional wood decking. Metal roof decking is known for its strength and fire-resistant properties, making it an ideal choice for both commercial and industrial buildings. Additionally, metal decks are lightweight, reducing the overall weight on the structure, and can be used as a base for various roofing systems.
They also provide superior moisture resistance, which helps to prevent issues like rot or mold that are more common in wood decking. Although metal decking may have a higher upfront cost compared to OSB or plywood, its durability and minimal maintenance requirements make it a smart long-term investment for specific applications, particularly in areas with harsh weather conditions.
Also Read: Do You Need A Permit To Replace A Roof?
Start Your Roof Replacement On The Right Note!
Choosing the right roof sheathing material is a crucial step in ensuring a strong and long-lasting roof. While OSB and plywood each have their advantages and drawbacks, both are widely used and can provide excellent structural support when properly installed.
If you’re unsure which material is best for your roof, consulting with a professional roofing contractor can provide clarity. At A. Fricker Roofing and Waterproofing, we have years of experience in roof repair and replacement, and we can help you select the best materials for your home’s unique needs.
Contact us today at (918) 402-7167.
