What Plywood Is Used For Roofing: Guide To Types, Grades, And Best Practices In The U.S.

Choosing the right plywood for roofing is crucial for the durability, safety, and performance of your structure. This comprehensive guide explores what plywood is used for roofing in American homes, from types and grades to thickness standards and building codes. Whether you’re a contractor or a homeowner, this article provides all you need to know for a successful roofing project.

Types Of Plywood Commonly Used For Roofing

The selection of plywood for roofing applications depends on weather exposure, load requirements, and budget. Two main types dominate American roofing projects: CDX plywood and OSB (Oriented Strand Board). Both have unique features that make them suitable for residential and commercial roofs.

CDX Plywood

CDX plywood is a type of softwood plywood with a “C” grade front, “D” grade back, and “X” indicating exterior glue. It’s strong, moisture resistant, and affordable, making it popular for roof sheathing where it will be covered by shingles or other materials.

• Durability: Handles temporary exposure to the elements
• Common Thicknesses: 1/2″, 5/8″, and 3/4″
• Standard Sizes: 4’x8′ panels
• Application: Roof deck, roof substrate under felt or waterproofing

Oriented Strand Board (OSB)

OSB is a composite board made from wood strands compressed with adhesives. It’s widely used due to its cost-effectiveness and consistent strength throughout the panel.

• Durability: Good moisture resistance
• Sizes & Thickness: Similar to CDX
• Cost: Generally less expensive than plywood
• Application: Roof sheathing for most residential builds

Plywood Vs. OSB For Roofing

Both CDX plywood and OSB are approved for roof sheathing by building codes. However, plywood withstands moisture better and dries faster than OSB. OSB, while economical, is slower to dry out, increasing the risk for swelling if exposed to water for extended periods.

• Plywood is preferred in wet, humid climates
• OSB is common in budget-focused or large developments

Roof Sheathing Plywood Grades And Ratings

Plywood comes in specific grades, each indicating surface quality and allowed defects. Roofing jobs generally use grades suitable for structural integrity rather than aesthetics.

Plywood Grade	Description	Recommended Roofing Use
A-B	High-quality faces, few flaws	Rare, costly, not typical for roof sheathing
B-C	Moderate quality, some imperfections	Not cost-effective for basic roofs
C-D (CDX)	Utility grade, suitable for covering	Most common for roof sheathing

CDX plywood is the industry standard due to its balance of durability, structural rating, and price point.

Plywood Thickness Standards For Roof Sheathing

Proper thickness is essential for roof strength and code compliance. The following are general recommendations for American homes:

• 1/2 inch (12 mm): Suitable for rafters/trusses spaced 16″ on center with light roofing materials like asphalt shingles.
• 5/8 inch (15 mm): Used where trusses/rafters are 24″ on center or in areas subject to snow load.
• 3/4 inch (18 mm): Required for heavy roofing materials or where extra strength is needed.

Always consult building codes and manufacturer installation guides for the correct thickness in your region and application.

Key Properties Of Roofing Plywood

Several properties distinguish the best plywood for roofing:

• Strength: Must support wind, snow, and maintenance loads
• Moisture Resistance: Essential for withstanding accidental exposure
• Span Rating: Marked on the panel, shows maximum allowable spacing between supports
• Edge Support: Tongue-and-groove (T&G) panels may be required for wider spans
• Grain Direction: Panels installed perpendicular to framing for optimal strength

Understanding APA Ratings And Labels

Roof sheathing panels are commonly marked with an APA (The Engineered Wood Association) stamp. This rating ensures the plywood complies with U.S. building standards.

• Span Rating: Two numbers separated by a slash (e.g., 32/16) indicate maximum allowable span for roof and floor use
• Exposure 1: Indicates suitability for limited exposure to moisture
• Exposure 2/Exterior: Higher resistance, but generally not required for roof sheathing under underlayment

Check for the APA panel grade stamp before purchase to ensure compliance and reliability.

Common Sizes And Weight Considerations

Most plywood for roofing is sold in 4’x8′ sheets. This size balances material coverage and ease of installation.

• 1/2″ sheet: 40-60 lbs
• 5/8″ sheet: 48-70 lbs
• 3/4″ sheet: Up to 80 lbs or more

Plan for the weight during lifting and moving panels onto the roof. Use appropriate equipment and safety procedures.

Local Building Codes And Roofing Plywood Requirements

Building codes differ by region, especially due to wind, snow, or hurricane risks. Most American jurisdictions refer to the International Residential Code (IRC). Always consult your city’s or county’s code for:

• Minimum plywood thickness
• Required span ratings
• Nailing schedules and edge support
• Moisture barriers and underlayments

Moisture Management With Roof Plywood

Protecting the plywood from moisture is essential for the roof’s longevity. Key steps include:

• Installing an underlayment (roof felt or synthetic membrane) directly over plywood sheathing
• Ensuring proper attic ventilation to allow drying of incidental moisture
• Promptly covering exposed plywood if installation is delayed

Plywood with water-repellent treatments is available for extra protection, but standard CDX is typically sufficient when installed and covered promptly.

Best Practices For Installing Plywood Roof Sheathing

For optimal results and code compliance, follow these industry best practices:

1. Stagger End Joints: Reduce weak points by offsetting panel joints on adjacent rows
2. Leave 1/8″ Gaps: Allow for plywood expansion from moisture
3. Install With Correct Orientation: Face grain perpendicular to rafters/trusses for greater strength
4. Follow Nailing Schedule: Typically 6″ on edges, 12″ in the field with eight-penny nails
5. Use H-clips between panels where required for additional edge support on longer spans

Environmental Considerations: Plywood Choices For Roofing

Eco-conscious homeowners may opt for plywood made from sustainably managed forests (FSC or SFI certified) or low-formaldehyde adhesives. OSB, often made from fast-growing wood species, is sometimes viewed as more environmentally friendly due to resource utilization.

Cost Comparison: Plywood Vs. OSB For Roofing

Material	Average Cost (per 4’x8′ sheet)	Key Advantages	Key Drawbacks
Plywood (CDX)	$30 – $60	Better in wet climates, dries quickly	More expensive, heavier
OSB	$20 – $40	Less expensive, strong, uniform quality	Slower drying, may swell if exposed

Material prices fluctuate based on region and market conditions. Always verify current costs before purchasing for a specific project.

Plywood Alternatives For Roof Sheathing

Beyond plywood and OSB, some projects use structural panels like waferboard or composite panels, but these are rare in the U.S. for standard roofing. In specialized applications, such as hurricane zones, structurally insulated panels (SIPs) or marine plywood may be specified for additional strength or moisture protection.

Plywood For Special Roofing Systems

While CDX plywood and OSB suffice for asphalt shingle and metal roofs, unique roofing systems require special attention:

• Tile roofs: Often need thicker, stronger sheathing (5/8″ or 3/4″) due to high weight load
• Flat/Low-slope roofs: May use tongue-and-groove plywood or built-up panel systems for additional strength and seamless substrates
• Green roofs: Require moisture-proof layers under the plywood

Choosing The Right Plywood For Re-Roofing Projects

Inspect the current roof deck for rot, mold, or structural damage before overlaying new materials. While matching existing thickness is common, upgrading to a thicker or higher grade panel can enhance performance and lifespan.

• Repair or replace any soft, water-damaged, or structurally unsound sheathing
• Ensure appropriate ventilation to prevent future moisture problems

Frequently Asked Questions About Roofing Plywood

• Is “marine plywood” needed for roofs? Not typically. Marine plywood is more expensive and designed for continuous wetting, such as boats. CDX is sufficient for covered residential roofs.
• Can different thicknesses be mixed? Not recommended. Uniform thickness ensures even shingle installation and prevents weak spots.
• Should roof plywood be painted? Painting is unnecessary when using standard roofing materials and underlayment. Paint may impede drying and trap moisture.
• What if the plywood gets wet before roof installation? Allow it to dry completely before proceeding. Replace any panels with evidence of swelling or delaminating.

Summary Table: Key Points For Roofing Plywood Selection

Parameter	Recommendation
Type	CDX plywood or OSB
Thickness	Minimum 1/2″ (16″ OC) or 5/8″ (24″ OC)
Grade	CDX (C-D, X for exterior glue)
Moisture management	Keep covered and dry, use underlayment
Span rating	Check APA stamp, meets or exceeds rafter spacing
Cost	Plywood more costly, but superior in wet climates; OSB popular and affordable

Choosing Plywood For Roof Sheathing: Final Tips

Choosing the right plywood for roofing is about balancing strength, moisture resistance, cost, and code requirements. For most U.S. roofing projects, CDX plywood or OSB of the correct thickness will deliver long-lasting performance when installed properly.

Work with licensed professionals, follow local code, and prioritize quality when choosing roof sheathing materials for your home.