Wondering what plywood is best for roofing? Learn about types, sizes, and codes. Get expert tips on plywood vs. OSB and what works in California.
If you're planning a roof replacement or new installation, you might hear your contractor talk about the condition of your roof decking. But what exactly is roof decking, and what type of plywood is used for roofing?
Roof decking, also called sheathing, is the wooden base that supports all other roofing materials. It’s what shingles, underlayment, and insulation sit on. Picking the right type of decking isn’t just about meeting code—it's essential for long-term roof performance, especially in places like Fresno where heat and seasonal rain take their toll.
Roof decking has several important jobs:
If your decking is old, sagging, or damaged, it can lead to leaks, mold, and expensive repairs. That’s why it’s so important to understand the materials used—and why roofers might recommend replacing them during a re-roof.
Most residential roofs are decked using one of two materials: plywood or OSB (oriented strand board).
Plywood is made from thin layers of wood veneer that are glued together. It’s strong, flexible, and resists warping from moisture better than many other materials. In roofing, the most common type is CDX plywood, which is bonded with moisture-resistant adhesives and suitable for outdoor use.
OSB, on the other hand, is made from wood chips and resin. It’s a cost-effective alternative to plywood and performs well under many conditions. However, OSB is more likely to swell at the edges when exposed to moisture over time. That doesn’t mean it’s a bad choice—it just means installation and ventilation need to be done carefully.
In hot, dry areas like Fresno, either plywood or OSB can work well. Plywood is often preferred for its durability and better moisture performance, while OSB may appeal to homeowners on a tighter budget.
In most roofing projects, the standard size for plywood is 1/2-inch CDX. It’s sturdy enough to span the distance between rafters spaced 16 inches apart, which is standard in many homes. For homes with wider rafter spacing—say, 24 inches—contractors may use thicker 5/8-inch or even 3/4-inch plywood to prevent sagging.
The “CDX” label is important. The “C” and “D” refer to the grading of the front and back faces (C being smoother, D being rough), while the “X” means it’s intended for exterior use and treated to resist moisture.
Using the correct thickness helps prevent bowing or sagging, especially under heavy roofing materials like tile. Always check with your roofer to make sure they’re using the proper thickness based on your roof’s structure.
California homes, especially those in the Fresno area, have to meet a few extra requirements due to heat, fire risk, and building codes.
Make sure your roofing contractor understands these codes and pulls the necessary permits before work begins.
Even high-quality plywood can deteriorate over time. You may need to replace sections—or the entire roof deck—if you see:
If you're getting a roof replacement, the contractor will inspect the decking and recommend replacement if any of these issues are found. Some companies charge extra to replace decking, while others include a certain amount in the base price.
The installation process generally follows these steps:
Once the decking is down, the underlayment and roofing materials are installed over it.
Not sure what your roofer plans to use? Here are a few questions you can ask:
A reputable roofing company will answer these questions clearly and provide documentation if needed.
Material prices fluctuate, but here are some general ranges:
Depending on your roof size, you may need 40 to 60 sheets. That brings the material cost alone to roughly $1,500 to $3,000, not including labor.
Some roofing companies include minor decking replacement in their estimates. Be sure to ask if your quote covers decking or if it’s extra.
Choosing the right plywood for your roof is more than just a technical detail—it’s the foundation for the entire roofing system. Whether you're replacing a few sheets or installing a new roof from scratch, selecting the right material ensures better longevity, safer performance, and peace of mind.
If you're in the Fresno area and want expert advice on your roof decking or need a full roof inspection, our team is ready to help. We offer free, no-obligation estimates and can explain everything you need to know before you commit.
Let’s make sure your next roof starts on the right foundation.