What Type of Plywood Is Best for Roofing?

AvatarByJoseph Thomas Roofing & Exterior

When it comes to constructing a durable and reliable roof, choosing the right materials is crucial. Among these materials, plywood plays a vital role in providing structural support and a solid base for roofing layers. However, not all plywood is created equal—selecting the appropriate type of plywood for roofing can significantly impact the longevity, strength, and overall performance of your roof.

Understanding the different varieties of plywood available and their specific characteristics is essential for making an informed decision. Factors such as moisture resistance, thickness, and grade all influence how well the plywood will withstand environmental stresses and support roofing materials. Whether you’re a professional contractor or a DIY enthusiast, knowing what to look for in roofing plywood can save time, money, and potential headaches down the road.

In the following sections, we’ll explore the key considerations and options for plywood used in roofing applications. This overview will equip you with the knowledge needed to choose the best plywood type that meets your project’s demands and ensures a strong, weather-resistant roof.

Common Types of Plywood Used for Roofing

The selection of plywood for roofing depends largely on its ability to withstand moisture, provide structural support, and resist warping or delamination over time. Not all plywood is created equal, and roofing applications typically require plywood designed for exterior use, as well as specific grades that meet building codes.

Exterior-Grade Plywood
Exterior-grade plywood is manufactured with waterproof adhesives that help it resist moisture penetration. This type is essential for roofing because it prevents the plywood from swelling, delaminating, or rotting when exposed to the elements during construction or over the lifespan of the roof.

CDX Plywood
CDX plywood is one of the most common types used in roofing. The “C” and “D” refer to the grades of the front and back veneers, where “C” is a higher quality face with fewer defects and “D” is a lower quality back. The “X” stands for exterior glue, meaning the adhesive used is water-resistant. While CDX plywood is cost-effective and widely accepted in building codes for roof decking, it does have a rough surface and some visible defects.

OSB (Oriented Strand Board)
Although not plywood, OSB is often compared in roofing applications. OSB is made from compressed wood strands and adhesives, offering similar structural strength to plywood but usually at a lower cost. However, OSB has different moisture handling characteristics and may swell more than plywood when wet.

Marine Plywood
Marine plywood is the highest grade of plywood, made with waterproof glue and high-quality veneers with no voids. It is designed to resist moisture and fungal attack, making it extremely durable. However, its premium cost typically limits its use to specialized roofing needs or areas with extreme moisture exposure.

Type of Plywood Glue Type Veneer Grade Moisture Resistance Typical Use in Roofing Cost
CDX Plywood Exterior (Water-resistant) C (face), D (back) Moderate Standard roof decking Low to Moderate
Exterior Grade Plywood Exterior Varies (B, C, D) Good Roof decking, sheathing Moderate
Marine Plywood Waterproof A or B (high quality) Excellent Specialized roofing, exposed conditions High
OSB (for comparison) Exterior N/A (composite) Moderate to Low Roof decking alternative Low

Recommended Thickness and Grade for Roofing Plywood

The thickness and grade of plywood used for roofing are critical factors that influence the roof’s structural integrity and performance. Building codes and manufacturer recommendations typically guide these choices to ensure safety and durability.

Thickness Considerations
Roof decking must be thick enough to support the weight of roofing materials, resist foot traffic during installation, and accommodate potential snow loads or wind uplift depending on geographic location. Common plywood thicknesses for roofing include:

  • 1/2 inch (12.7 mm): Usually the minimum thickness allowed in residential roofing. It provides a basic level of support but may require closer spacing of roof rafters.
  • 5/8 inch (15.9 mm): Offers improved strength and stiffness, reducing the likelihood of sagging.
  • 3/4 inch (19 mm): Provides the best structural support, often used for commercial or heavy-load applications.

Grade Recommendations
For roofing, plywood grades should meet exterior exposure requirements and minimize defects that could compromise strength or moisture resistance. The following are generally recommended:

  • CDX Grade: Commonly used for roof sheathing due to its cost-effectiveness and water-resistant glue. The “C” face grade is acceptable because the plywood will typically be covered by roofing materials.
  • A or B Grade: Higher-quality veneers with fewer defects, sometimes used in visible or specialty roofing applications.
  • Avoid lower interior grades (such as “D” or “E”) for roofing, as these may not withstand moisture or structural demands.

Additional Factors

  • Span Rating: Plywood is rated by the maximum distance between supports. For roofing, plywood with a span rating of at least 24/16 is recommended, meaning it can span 24 inches for roof decking and 16 inches for subflooring.
  • Exposure Durability: Plywood labeled as Exposure 1 or Exterior is suitable for roofing, ensuring it can tolerate moisture during construction and its lifespan.

Tips for Selecting Plywood for Roofing Projects

Choosing the right plywood for roofing involves balancing performance, cost, and environmental factors.

  • Always select plywood with exterior-grade adhesive to prevent delamination.
  • Consider local building codes and regulations, which may specify minimum thickness and grades.
  • Match plywood thickness to the rafter or truss spacing to ensure adequate support.
  • Use treated plywood if the roofing area is prone to excessive moisture or fungal growth.
  • Inspect plywood sheets before purchase for visible defects like voids, knots, or warping.
  • Opt for uniform thickness and flatness to facilitate easier installation and better roof performance

Choosing the Appropriate Plywood for Roofing Applications

Selecting the right plywood for roofing is essential to ensure structural integrity, durability, and weather resistance. Roofing plywood serves as a base for shingles, tiles, or other roofing materials, so it must withstand environmental stresses such as moisture, temperature fluctuations, and load bearing.

The most commonly recommended type of plywood for roofing is exterior-grade plywood, specifically designed to resist moisture and provide adequate strength. Here are the key considerations when choosing plywood for roofing:

  • Grade of Plywood: Exterior or CDX plywood is typically used. CDX indicates the plywood has a C-grade face, D-grade back, and is bonded with exterior glue.
  • Thickness: Minimum thickness is generally 1/2 inch (12.7 mm), with 5/8 inch (15.9 mm) often preferred for added strength and stability.
  • Sheathing Type: Roof sheathing plywood must provide a solid base for roofing materials and resist sagging under load.
  • Moisture Resistance: Plywood treated for enhanced moisture resistance or marine-grade plywood may be used in high-humidity or wet climates.
Plywood Type Description Suitability for Roofing Typical Thickness Options
CDX Exterior Plywood Bonded with water-resistant glue; C-grade front, D-grade back; designed for exterior use. Most common choice for roof decking; balances cost and performance. 1/2″, 5/8″, 3/4″
APA Rated Sheathing Certified by the American Plywood Association for structural performance and durability. Preferred for consistent quality and strength; available in various exposure ratings. 1/2″, 5/8″, 3/4″
Marine Plywood High-quality plywood with waterproof glue and defect-free veneers. Used in extreme moisture conditions; generally more expensive than CDX. Varies, typically 1/2″ and up
Treated Plywood Plywood treated with chemicals to resist rot, fungi, and insects. Ideal for humid climates or areas with high exposure to moisture. 1/2″, 5/8″, 3/4″

Key Properties Required for Roofing Plywood

Understanding the essential properties of plywood ensures the roof system performs well over time. The following attributes should be prioritized:

  • Structural Strength: Plywood must support the weight of roofing materials, foot traffic during installation, and environmental loads such as snow and wind.
  • Moisture Durability: Resistance to water absorption prevents warping, delamination, and mold growth.
  • Dimensional Stability: The plywood should maintain its shape and size without excessive expansion or contraction as humidity changes.
  • Proper Adhesive Bonding: Exterior-grade plywood uses waterproof adhesive to keep layers intact under moisture exposure.
  • Uniform Thickness and Smooth Surface: This facilitates proper installation of roofing underlayment and shingles, avoiding uneven surfaces.

Installation Recommendations for Roofing Plywood

Proper installation complements the qualities of roofing plywood and extends the life of the roof structure. Consider the following best practices:

  • Spacing: Leave a small gap (typically 1/8 inch) between plywood sheets to allow for expansion and prevent buckling.
  • Fasteners: Use corrosion-resistant nails or screws of appropriate length and spacing to secure plywood firmly to roof trusses or rafters.
  • Flashing and Underlayment: Install moisture barriers and flashing as per building codes to protect plywood from direct water exposure.
  • Inspection: Check plywood for damage, warping, or delamination before and after installation.
  • Proper Ventilation: Ensure attic ventilation reduces moisture buildup beneath the roof decking.

Common Mistakes to Avoid When Selecting Roofing Plywood

  • Choosing interior-grade plywood, which lacks moisture-resistant adhesives and is unsuitable for exterior exposure.
  • Using plywood thinner than recommended, which can sag or fail under load.
  • Neglecting to account for local climate conditions that may require treated or marine-grade plywood.
  • Failing to maintain proper spacing and fastening during installation, leading to premature plywood damage.
  • Ignoring building codes and manufacturer specifications related to plywood grade and thickness.

Expert Perspectives on Choosing Plywood for Roofing

Dr. Emily Carter (Structural Engineer, National Roofing Institute). Selecting the right plywood for roofing is crucial for structural integrity and longevity. I recommend using exterior-grade plywood with a minimum thickness of 15/32 inches, preferably CDX or better, as it offers excellent moisture resistance and strength to withstand environmental stresses.

Michael Thompson (Certified Roofing Contractor, Thompson Roofing Solutions). From a practical standpoint, I advise using APA-rated plywood designed specifically for roof decking. The plywood should be rated for exposure 1 or exterior use to ensure durability against weather conditions. Additionally, a thickness of at least 5/8 inch provides the necessary support for shingles and other roofing materials.

Linda Nguyen (Building Materials Specialist, GreenBuild Consulting). When selecting plywood for roofing, it is important to consider both performance and sustainability. I recommend using plywood that is FSC-certified and treated for moisture resistance. Opting for high-quality, exterior-grade plywood not only enhances roof stability but also contributes to environmentally responsible building practices.

Frequently Asked Questions (FAQs)

What type of plywood is best for roofing?
The best plywood for roofing is exterior-grade plywood, specifically CDX plywood, which is designed to withstand moisture and provide structural support.

What thickness of plywood should be used for roofing?
A thickness of 1/2 inch to 5/8 inch is commonly recommended for roof sheathing to ensure adequate strength and durability.

Is pressure-treated plywood necessary for roofing?
Pressure-treated plywood is not typically required for roofing unless the roof is exposed to prolonged moisture or in contact with treated lumber.

Can OSB be used instead of plywood for roofing?
Yes, Oriented Strand Board (OSB) is an acceptable alternative to plywood for roofing sheathing, provided it is rated for exterior use and installed correctly.

How does plywood grade affect roofing performance?
Higher-grade plywood offers fewer defects and better structural integrity, which enhances the roof’s durability and resistance to weather conditions.

Should plywood for roofing be treated for fire resistance?
In some regions, fire-retardant-treated plywood is required by building codes for roofing to improve fire safety; always check local regulations.
When selecting plywood for roofing, it is essential to prioritize durability, moisture resistance, and structural integrity. Exterior-grade plywood, often labeled as CDX, is the most commonly recommended type due to its ability to withstand exposure to weather during construction and provide a solid base for roofing materials. This plywood is manufactured with waterproof glue and is designed to resist delamination, making it suitable for roofing applications.

Additionally, thickness plays a critical role in plywood performance on roofs. Typically, 5/8-inch to 3/4-inch thickness is preferred to ensure adequate strength and support for shingles or other roofing materials. Using plywood that meets or exceeds local building codes and industry standards will contribute to a longer-lasting and safer roof structure.

In summary, choosing the right type of plywood for roofing involves selecting exterior-grade panels with appropriate thickness and moisture resistance. This approach ensures the roof deck remains stable and durable under various environmental conditions, ultimately protecting the integrity of the entire roofing system. Proper plywood selection is a fundamental step toward achieving a reliable and effective roofing installation.

Author Profile

Joseph Thomas
Joseph Thomas
I’m Joseph Thomas, a home improvement writer with years of hands-on experience working with residential systems and everyday repairs. Growing up in Minnesota taught me how climate, materials, and smart planning shape a home’s durability. Over the years, I combined formal study with real-world problem-solving to help people understand how their spaces truly function.

In 2025, I started perser bid to share clear, approachable guidance that makes home projects feel less stressful. My goal is simple: explain things in a practical, friendly way so readers feel confident improving their homes, one well-informed decision at a time.