When it comes to structural sheathing for roofs, walls, and floors, two materials dominate the market: oriented strand board (OSB) and plywood. Both are engineered wood panels, but they have distinct differences that can affect your project's cost, durability, and performance. Understanding these differences is crucial for making the right choice.

Cost and Availability

OSB is generally more affordable than plywood, often costing 20-30% less per sheet. This makes it a popular choice for large-scale projects where budget is a concern. However, plywood prices have become more competitive in recent years, and it remains widely available.

Strength and Stiffness

Plywood is known for its excellent stiffness and nail-holding ability, especially in thinner panels. OSB, on the other hand, is slightly more flexible but provides superior shear strength in thicker sheets (7/16 inches or more). For roof sheathing, OSB's larger panel size (up to 8x24 feet) reduces seams and potential leak points.

Moisture Resistance

This is the biggest differentiator. Plywood resists moisture better, especially if it is exterior-grade (CDX). When exposed to rain or humidity, plywood swells less and returns to its original shape better than OSB. OSB edges are more vulnerable to moisture—if water penetrates the edges, the panel can swell, delaminate, and lose structural integrity. For bathroom and roof sheathing in humid climates, plywood is often preferred.

Installation and Handling

OSB is heavier and less forgiving during cutting. It creates more dust and can be more difficult to work with in tight spaces. Plywood is lighter, easier to cut precisely, and produces fewer splinters. However, OSB’s rough surface offers better traction for roofing walkways.

Fire Resistance

Both materials have similar fire resistance, but plywood generally chars more slowly. For code compliance, fire-rated versions are available for both.

Conclusion

For budget-friendly, large-area sheathing with fewer seams, OSB is a solid choice—especially for roof decks in dry climates. For projects requiring superior moisture resistance and long-term durability, plywood is the better option. Ultimately, the decision should factor in your local climate, building code, and project timeline.