OSB or Plywood for Metal Roofing: Which is Better Choice

Selecting the right roof deck substrate is essential for the longevity and performance of a metal roofing system. Whether it’s a commercial or residential structure, the choice between OSB (Oriented Strand Board) and plywood directly impacts the durability, weather resistance, insulation, and load-bearing capacity of the roofing system.

This guide provides an expert comparison of these two sheathing materials, discussing installation techniques, attachment methods, structural integrity, compliance with building codes, and cost-efficiency.

2. OSB vs. Plywood: Composition & Manufacturing

Understanding OSB (Oriented Strand Board)

• OSB is an engineered wood panel made from wood chips, glued, pressed, and bonded under heat and pressure to form thin sheets.
• It is commonly used as a cost-effective sheathing option in construction projects.
• OSB panels offer good structural strength but are more susceptible to moisture saturation, swelling, and delamination.

Understanding Plywood

• Plywood is made of cross-laminated wood veneer that is bonded with resin and pressed under high pressure.
• The cross-graining technique enhances stiffness, stability, and strength, making it ideal for roofing applications.
• Plywood’s moisture resistance is superior to OSB, reducing the risk of swelling, decay, and separation.

3. Strength, Load-Bearing Capacity & Fastener Retention

Load-Bearing Capacity

• Plywood has a higher weight-bearing capacity compared to OSB, making it ideal for heavy roofing materials, open framing installations, and hurricane zones.
• OSB can support significant loads but may require additional reinforcement layers for stability.

Fastener Retention & Pull-Out Values

• Plywood provides better fastener attachment and pull-out values, meaning nails, screws, and clips hold more securely over time.
• OSB tends to lose fastener grip, especially in humid environments, which can compromise the structural integrity of a metal roofing system.
• Recommended fastener sizes include #10, 13×1”, pancake-head screws, and #12 or #14s for secure fastening systems.

4. Moisture Resistance, Weatherproofing & Longevity

Moisture & Humidity Concerns

• Plywood withstands moisture exposure better than OSB.
• OSB tends to absorb water, leading to swelling and structural weakening.
• Proper venting and insulation help mitigate moisture-related issues in metal roofing applications.

Weather Resistance & Environmental Impact

• Plywood performs better in extreme weather conditions such as heavy rain, snow, and hailstorms.
• OSB is more susceptible to weather-related deterioration unless it is properly sealed or covered with peel-and-stick underlayment.

Thermal Resistance & Energy Efficiency

• Plywood offers better thermal resistance, preventing heat buildup under the metal roof.
• OSB traps more heat, potentially impacting the energy efficiency of a roofing system.

5. Cost Considerations & Affordability

• OSB is generally more cost-efficient, making it a popular choice for budget-conscious projects.
• Plywood has a higher price point due to its manufacturing process and superior performance.
• The overall price for a 4×8 plywood sheet is higher than a comparable OSB panel.
• Labor costs for OSB installation are often lower, but long-term maintenance expenses can be higher.

6. Installation Process, Methods & Best Practices

Ease of Installation

• OSB is heavier, making handling and cutting more labor-intensive.
• Plywood is lightweight, allowing for easier installation and maneuvering.
• Proper fastener spacing, attachment techniques, and flashing installation are critical for ensuring a weathertight roofing system.

Fastening Systems & Sheathing Support

• Fastening systems include self-drilling screws, clip attachments, and mechanical seams.
• Plywood provides stronger fastening security, especially in open purlins and structural decking installations.
• OSB requires additional reinforcement, such as furring strips or foam insulation layers, for better attachment stability.

7. Suitability for Metal Roofing Applications

Roofing Techniques & Compatibility

• Plywood is the preferred choice for metal roofing systems, offering better compatibility with fastener requirements and long-term weather durability.
• OSB can be used but needs additional layers of waterproofing for increased resistance against moisture, humidity, and temperature fluctuations.

Compliance with Building Codes & Industry Standards

• Both OSB and plywood must comply with UL 580, UL 1897, and ASTM E 1592 testing standards for wind uplift resistance.
• Plywood is more compliant with fire-rated requirements, making it a safer choice for residential structures.

8. Expert Recommendations & Conclusion

Which Is the Best Choice for Metal Roofing?

When it comes to metal roofing applications, plywood stands out as the superior choice due to its exceptional moisture resistance, stronger fastener retention, and better load-bearing performance. It holds screws, nails, and clips more securely, ensuring long-term structural stability. Additionally, plywood resists swelling, warping, and decay, making it a durable and low-maintenance option for both residential and commercial roofing systems.

On the other hand, OSB can be a budget-friendly alternative, but it requires proper weatherproofing, sealing techniques, and additional reinforcement to maintain its structural integrity. Since OSB is more prone to moisture absorption, edge swelling, and fastener pull-out issues, it’s crucial to use high-retention screws and protective coatings to enhance its longevity.

Ultimately, plywood is the best choice for metal roofing when durability and strength are priorities. However, for those seeking a cost-effective option, OSB can work if installed with the right sealing and reinforcement techniques to withstand weather conditions and maintain structural stability.