Roof Decking: Plywood vs OSB for Florida Roofs

When most homeowners think about their roof, they picture shingles, tiles, or metal panels. But beneath every visible roofing material sits the structural layer that holds it all together: the roof decking, also called roof sheathing. This layer of sheet material spans your trusses or rafters and provides the nailing surface for underlayment and roofing materials. It is also the structural component that transfers wind uplift forces from the roof covering to the framing below.

In most of the United States, the choice between plywood and oriented strand board (OSB) for roof decking is primarily a cost decision. OSB costs less, both materials perform adequately in moderate climates, and builders default to whichever is cheaper that month. But Florida is not most of the United States. The combination of extreme humidity, daily afternoon thunderstorms during summer, hurricane exposure, and strict building codes makes the plywood vs. OSB decision far more consequential in Pinellas County than it is in Ohio or Oregon.

This guide breaks down the differences between plywood and OSB for Florida roof decking, explains when each is appropriate, covers the relevant Florida Building Code requirements, and gives you the practical information you need to make the right call for your home.

What Is Roof Decking and Why Does It Matter?

Roof decking is the layer of sheet goods (typically 4-foot by 8-foot panels) nailed directly to the top of your roof trusses or rafters. It serves three critical functions. First, it provides the structural surface that your underlayment, drip edge, and roofing materials are attached to. Second, it acts as a structural diaphragm that distributes wind and dead loads across the roof framing. Third, during a hurricane, it is the primary barrier preventing wind-driven rain from entering your attic if the roof covering is compromised.

In Florida, that third function is arguably the most important. When a hurricane strips off shingles or tiles, the decking is your last line of defense against catastrophic water intrusion. If the decking is solid, water entry is limited. If the decking has delaminated, rotted, or lost its fastener integrity, entire panels can lift off in the wind, exposing your attic and everything below to the full force of the storm.

Florida's roofing nailing schedule (the specific pattern and spacing of nails attaching decking to trusses) is among the strictest in the country precisely because of this. The 2023 Florida Building Code, 8th Edition, requires 8d ring-shank nails at 6 inches on center along panel edges and 12 inches on center in the field for most wind zones in Pinellas County. Some HVHZ areas require even tighter spacing.

Plywood (CDX): The Florida Favorite

When roofers in Pinellas County say "plywood," they almost always mean CDX plywood. The "C" and "D" refer to the veneer grades on the front and back faces (C is the better side, D is the rougher side), and the "X" stands for exposure, meaning the adhesive is rated for temporary moisture exposure during construction. CDX is not rated for permanent outdoor exposure, but it handles intermittent wetting and drying far better than OSB.

CDX plywood is manufactured by layering thin sheets of wood veneer (called plies) at alternating 90-degree angles and bonding them with waterproof adhesive under heat and pressure. A typical 15/32-inch CDX panel has five plies. This cross-grain construction is the key to plywood's performance advantages. Because the grain direction alternates with each layer, plywood resists expansion and contraction in both directions, distributes loads more evenly, and maintains its dimensional stability even after repeated wetting and drying cycles.

Plywood Strengths for Florida Roofs

• Superior moisture handling: Plywood absorbs moisture more slowly than OSB and releases it much faster. In Florida, where afternoon thunderstorms are a near-daily event from June through September, this quick drying capability is critical. A plywood panel that gets wet during installation will typically dry to acceptable moisture levels within 24-48 hours.
• No permanent edge swell: Unlike OSB, plywood does not suffer from permanent edge swelling when exposed to moisture. It may warp slightly when wet, but it returns to its original dimensions when it dries.
• Better nail holding after wetting: When plywood gets wet and dries, it maintains most of its nail withdrawal resistance. This matters enormously during hurricanes, when the nails connecting decking to trusses are the primary structural connection resisting wind uplift.
• Longer track record in Florida: Plywood has been the standard roof decking material in Florida for decades. Roofers, inspectors, and engineers are all intimately familiar with how it performs in this climate over 20, 30, and 40-year timelines.
• Easier to identify damage: Damaged plywood is straightforward to spot during inspections. Delamination, rot, and water staining are all visible and obvious. OSB damage can be harder to assess because the compressed strand structure can look intact even when compromised.

Plywood Weaknesses

• Higher cost: CDX plywood costs $5-10 more per sheet than comparable OSB, and the gap can widen during periods of high demand (like after a hurricane season).
• Less uniform thickness: Plywood thickness can vary slightly from panel to panel due to the natural veneer manufacturing process. This variation is minor (typically less than 1/32 inch) but can occasionally create slight unevenness in the roof surface.
• Weight: Plywood is slightly heavier than comparable OSB panels, though the difference (a few pounds per sheet) is negligible for structural calculations.

OSB (Oriented Strand Board): The Budget Option

Oriented strand board is manufactured by compressing large wood strands (typically 3-6 inches long) with waterproof adhesive under extreme heat and pressure. The strands are oriented in specific directions in each layer, similar in concept to plywood's cross-grain construction but using strands instead of continuous veneers.

OSB dominates the national market for roof sheathing. It accounts for roughly 70% of all structural sheathing used in residential construction across the United States. The reasons are straightforward: OSB is cheaper, it is more dimensionally consistent (uniform thickness from panel to panel), and it is available in larger panel sizes for commercial applications.

But OSB's national dominance does not translate to universal suitability. In dry climates like Arizona or moderate climates like the Pacific Northwest, OSB performs perfectly well on roofs for decades. In Florida's subtropical environment, OSB faces challenges that don't exist in those regions.

OSB Strengths

• Lower cost: OSB typically costs $5-10 less per sheet than CDX plywood. On a full roof replacement requiring 80-120 sheets, that translates to $400-1,200 in material savings.
• Consistent thickness: OSB panels are manufactured to extremely tight thickness tolerances, creating a very uniform roof surface. This is particularly noticeable with architectural shingles, which can telegraph minor surface irregularities.
• Engineered strength: OSB's structural properties (span ratings, load-bearing capacity) meet or exceed plywood's at equivalent thicknesses. A 7/16-inch OSB panel has the same span rating as a 15/32-inch plywood panel.
• Environmental argument: OSB uses smaller, fast-growing trees and produces less waste during manufacturing than plywood, which requires large-diameter logs.

OSB Weaknesses in Florida

• Catastrophic edge swell: This is the single biggest concern with OSB in Florida. When cut edges or damaged areas are exposed to moisture, the wood strands absorb water and swell permanently by 15-25% in thickness. These swollen edges create ridges that telegraph through shingles and never flatten back out, even after drying completely.
• Slow drying: OSB absorbs moisture more slowly than plywood but releases it much more slowly. A soaked OSB panel can take two to three weeks to dry to acceptable levels, compared to one to two days for plywood. In Florida's humid environment, that slow drying means prolonged moisture exposure to your roof structure.
• Reduced nail holding when wet: When OSB absorbs moisture, the strands soften and nail withdrawal resistance drops significantly. If a hurricane arrives while your OSB decking is still holding moisture from a recent rain event, those fastener connections are weaker than they should be.
• Difficult damage assessment: OSB can look structurally sound from above while being severely compromised underneath. The top surface strands can maintain their appearance even when the interior has begun to degrade from trapped moisture.
• Delamination pattern: When plywood fails, it tends to delaminate in visible layers that are easy to spot. When OSB fails, the strands lose their bond with the adhesive and the panel gradually turns soft and spongy. This failure mode is harder to catch during a visual inspection.

Plywood vs. OSB: Direct Comparison for Pinellas County

Florida Building Code Requirements for Roof Decking

The Florida Building Code (FBC) establishes minimum requirements for roof decking that are stricter than the International Building Code (IBC) used in most other states. These requirements reflect Florida's unique combination of hurricane-force winds, heavy rain, and the critical role that roof sheathing plays in protecting occupied spaces during severe weather events.

Minimum Thickness Requirements

For residential construction in most of Pinellas County (wind speeds of 150-170 mph per the FBC 8th Edition), the minimum roof decking thickness is 15/32 inch for plywood or 7/16 inch for OSB, assuming standard 24-inch on-center truss spacing. These two thicknesses have equivalent structural span ratings, meaning they can support the same loads over the same unsupported spans.

However, many roofing contractors and structural engineers in Pinellas County recommend upgrading to 19/32-inch (5/8-inch) plywood, particularly on homes in higher wind zones or older homes where truss spacing may not be perfectly consistent. The added thickness provides a safety margin, better nail holding, and increased resistance to wind uplift forces.

HVHZ (High-Velocity Hurricane Zone) Requirements

Florida's High-Velocity Hurricane Zones apply to Miami-Dade and Broward counties, not Pinellas County directly. However, portions of coastal Pinellas County fall under design wind speeds that approach HVHZ levels (170+ mph 3-second gust). In these high-wind areas, the code requires enhanced fastening schedules, and some inspectors and engineers will specify plywood over OSB because of its superior moisture resistance and nail-holding capacity after wetting.

When a product approval is required (which is increasingly common in Florida's stricter permitting environment), plywood products have a longer and more established approval history than OSB products for high-wind applications. This does not mean OSB cannot be used, but it does mean that the contractor needs to verify that their specific OSB product has the appropriate Florida Product Approval for the wind speed and building configuration.

Fastener Requirements

Florida's roof decking fastener schedule is one of the strictest in the nation:

• Nail type: 8d ring-shank nails (2-3/8 inch length, 0.113 inch diameter) are the standard for most Pinellas County applications
• Edge spacing: 6 inches on center along all panel edges
• Field spacing: 12 inches on center at intermediate supports (6 inches in higher wind zones)
• Edge distance: Nails must be at least 3/8 inch from panel edges
• Panel gaps: 1/8 inch gap required between panels to allow for thermal expansion

These fastener requirements apply equally to plywood and OSB. However, the practical reality is that ring-shank nails hold better in plywood's cross-grain veneer structure than in OSB's compressed strand structure, particularly after the panel has gone through wetting and drying cycles.

Moisture Performance: The Critical Difference in Florida

If there is one factor that should drive your plywood vs. OSB decision in Pinellas County, it is moisture performance. Florida's climate subjects roof decking to moisture stress that simply does not exist in most other parts of the country.

How Florida's Climate Attacks Roof Decking

Consider what your roof decking endures during a typical Florida summer. Morning humidity regularly exceeds 90%. Afternoon thunderstorms dump heavy rain at least three to four days per week from June through September. Attic temperatures can reach 150 degrees Fahrenheit, creating a massive temperature differential between the top and bottom surfaces of the decking. And if you have any roof penetrations (vents, skylights, pipe boots) that develop even minor leaks, moisture can contact the decking continuously for weeks or months before anyone notices.

During roof replacement, the decking is fully exposed to the elements for hours or even days. A roofer who strips your old roof on a Monday morning and has a surprise thunderstorm roll through at 3 PM has just soaked every sheet of decking on your roof. With plywood, that's a one-day setback. With OSB, that single rain event can create permanent edge swelling that shows through your new shingles for the life of the roof.

The Edge Swell Problem

Edge swelling is OSB's Achilles' heel in Florida, and it deserves detailed explanation because it is the single most common defect roofers in Pinellas County encounter with OSB decking.

When an OSB panel is cut (either at the factory edges or during installation), the compressed wood strands at the cut edge are exposed. These strands act like tiny sponges when water contacts them. They absorb moisture and swell in thickness, sometimes expanding 15-25% at the edge compared to the center of the panel. This expansion is largely permanent because the adhesive bonds between strands break during the swelling process and do not re-form when the panel dries.

The result is a visible ridge at every panel seam. Roofers call these "ghost lines" because they show through the finished roof covering like phantom lines running across the roof surface. With asphalt shingles, ghost lines from OSB edge swell are visible from the ground and are a common source of homeowner complaints and warranty claims.

Some OSB manufacturers have developed edge-sealed products that include a water-resistant coating on the factory edges. These products (like LP's TechShield or Weyerhaeuser's Edge Gold) do reduce factory-edge swelling. However, every on-site cut still exposes raw strands, and roof installations require dozens of cuts for hips, valleys, ridges, and penetrations. Edge sealing helps but does not eliminate the problem in Florida's wet environment.

When Plywood Is the Clear Winner in Pinellas County

While OSB can work acceptably on Florida roofs in certain situations, there are specific scenarios where plywood is the clearly superior choice:

• Coastal properties: Homes within 3,000 feet of the Gulf of Mexico or Tampa Bay face higher humidity, salt air exposure, and wind-driven rain. Plywood's superior moisture handling makes it the safer choice in these locations.
• Low-slope roof sections: Any roof section below 4/12 pitch is more susceptible to water pooling and slower drainage. Plywood tolerates this occasional standing water better than OSB.
• Homes with a history of leaks: If your roof has experienced leaks in the past, the replacement decking should be plywood. Any residual moisture in the framing or adjacent panels will stress new OSB more than plywood.
• Premium roofing materials: If you are investing in stone-coated steel, clay tile, or other 50-year roofing materials, it makes no sense to use budget decking underneath. The decking needs to last as long as the material above it.
• Insurance considerations: Some Florida insurers are beginning to differentiate between plywood and OSB in their underwriting. While not universal, using plywood can occasionally help with premium calculations or avoid pushback during the inspection process.
• Older homes with irregular framing: Many older Pinellas County homes (pre-1990) have truss spacing that varies slightly from the standard 24-inch centers. Plywood's cross-grain construction is more forgiving of minor framing irregularities than OSB.

When OSB Is Acceptable in Pinellas County

OSB is not inherently bad for Florida roofs. Millions of Florida homes have OSB decking that has performed adequately for years. Situations where OSB is a reasonable choice include:

• Budget-constrained projects: When every dollar matters and the home is inland (not coastal), OSB saves $400-1,200 on a typical residential reroof. That money can be redirected to better underlayment or impact-resistant shingles.
• New construction with quick dry-in: On new builds where the roof is sheathed and dried in (underlayment applied) within the same day, OSB's moisture vulnerabilities are minimized because the panels never get wet.
• Inland properties: Homes in central Pinellas County, away from direct coastal exposure, experience slightly less moisture stress than beachfront properties.
• When paired with premium underlayment: A high-quality synthetic underlayment or peel-and-stick membrane over OSB provides an extra moisture barrier that compensates for some of OSB's weaknesses.

If you do choose OSB, insist on edge-sealed panels, ensure the panels are stored off the ground and covered before installation, and make sure your contractor has a dry-in plan that minimizes exposure time during installation.

Cost Breakdown: Plywood vs. OSB for a Typical Pinellas County Roof

The cost difference between plywood and OSB on a full roof replacement is real but modest in the context of the total project cost. A typical Pinellas County reroof costs $15,000-40,000 depending on the roofing material chosen. The $400-1,200 savings from choosing OSB over plywood represents roughly 2-5% of the total project cost. For that relatively small savings, you are accepting meaningfully higher moisture risk in one of the most moisture-intensive climates in the country.

Partial Decking Replacement: What to Expect During a Reroof

Full decking replacement is relatively uncommon during a standard reroof. What happens far more often is partial replacement: after the old roofing material and underlayment are stripped, the crew walks the entire deck and identifies panels that need replacement due to rot, delamination, water damage, or soft spots.

In Pinellas County, it is typical for 5-20 sheets of decking to need replacement during a reroof, depending on the age of the home, the condition of the previous roofing system, and whether any chronic leaks existed. At $75-100 per sheet installed, partial decking replacement adds $375-2,000 to most reroofing projects.

Your roofing contract should include a per-sheet price for decking replacement so there are no surprises. Reputable contractors in Pinellas County will photograph each damaged panel, show it to you (or document it for your records), and charge the agreed-upon rate. Be wary of contractors who quote a suspiciously low per-sheet replacement price, as this sometimes indicates they plan to skip necessary replacements or use substandard material.

When replacing individual panels during a reroof, always match the existing material and thickness. If your home has plywood decking and a few sheets need replacement, use plywood. Mixing plywood and OSB panels on the same roof is not a code violation, but it creates inconsistencies in how the roof system handles moisture and can lead to differential movement at the seams between dissimilar materials.

Special Considerations for Pinellas County Homes

Homes Built Before 2002

If your Pinellas County home was built before 2002 (when the current Florida Building Code was adopted, replacing the older Standard Building Code), there is a good chance your original decking was thinner than current code requires. Many pre-2002 homes used 3/8-inch plywood or 3/8-inch OSB, which does not meet current minimum thickness standards.

When you reroof a pre-2002 home, the new roof must comply with current code. If your existing decking is thinner than 15/32 inch (plywood) or 7/16 inch (OSB), the building department may require full decking replacement, even if the existing panels are in good condition. This is an important budget consideration that you should discuss with your contractor during the estimate process.

Homes With Tile Roofs

Concrete and clay tile roofs are heavy. A concrete tile roof can weigh 900-1,200 pounds per roofing square (100 square feet), compared to 200-300 pounds for asphalt shingles. This added weight puts more static load on the decking, and the Florida Building Code requires that decking under tile roofs meet specific structural requirements.

For tile roofs in Pinellas County, 19/32-inch (5/8-inch) plywood or equivalent OSB is commonly specified, and many engineers prefer 23/32-inch (3/4-inch) plywood for the added stiffness and nail-holding capacity. The extra cost of thicker plywood is small relative to the overall cost of a tile roof installation, and the structural benefit is substantial.

Hurricane Damage Patterns

Post-hurricane damage assessments in Florida consistently show that roof decking failure is a leading cause of catastrophic home damage. When decking panels separate from the trusses, everything above them goes with the wind, and everything below them is exposed to rain intrusion.

Studies of hurricane damage patterns have found that the most common points of decking failure are panel edges and corners, particularly at gable ends where wind uplift forces are highest. Plywood's cross-laminated construction provides more consistent performance at edges and corners than OSB's strand construction, which is one of the reasons structural engineers in hurricane-prone areas tend to favor plywood.

What Your Roofer Should Tell You About Decking

A good Pinellas County roofing contractor should discuss decking with you during the estimate process. Here are the questions to ask and the answers to expect:

• "What type of decking will you use for replacements?" The answer should be specific: CDX plywood or a named OSB product. "Whatever's at the lumberyard" is not an acceptable answer.
• "What thickness?" Minimum 15/32-inch plywood or 7/16-inch OSB for standard applications, thicker for tile roofs or high-wind locations.
• "How much per sheet for replacements?" Expect $70-100 per sheet installed for plywood. Be cautious of prices below $50 or above $150.
• "How do you handle wet decking during installation?" The contractor should have a dry-in protocol: either tarp coverage for approaching weather or same-day underlayment application to protect exposed decking.
• "Will you document any decking that needs replacement?" Photos of every damaged panel should be standard practice. This documentation is also valuable for insurance claims.

Our Recommendation for Pinellas County Homeowners

For the vast majority of Pinellas County homeowners, CDX plywood is the better choice for roof decking. The $400-1,200 premium over OSB on a full deck replacement is a small insurance policy against moisture damage in one of the most humid climates in the country. For partial replacements (which is the more common scenario), the cost difference shrinks to $50-200 total, making the decision even more straightforward.

If budget is the primary concern and you choose OSB, do so with eyes open. Use edge-sealed panels, insist on same-day dry-in of all exposed decking, and pair the OSB with a premium synthetic underlayment. These steps won't eliminate OSB's moisture limitations, but they will reduce the risk to acceptable levels for most applications.

Regardless of which material you choose, make sure your contractor follows the Florida Building Code's fastener schedule to the letter. The nailing pattern is just as important as the panel material when it comes to hurricane resistance. A perfectly good plywood panel with substandard nailing is just as likely to fail in a hurricane as a compromised OSB panel with proper nailing. Both the material and the installation matter.

Frequently Asked Questions

Is plywood or OSB better for roof decking in Florida?

For most Florida homes, CDX plywood is the better choice for roof decking despite costing $5-10 more per sheet. Plywood handles moisture significantly better than OSB in Florida's high-humidity environment. OSB swells at the edges when exposed to moisture and can take weeks to dry, while plywood dries quickly and maintains its structural integrity. In High-Velocity Hurricane Zones and coastal areas of Pinellas County, plywood is strongly recommended.

What thickness of roof decking does Florida building code require?

The Florida Building Code requires a minimum of 15/32-inch (approximately 1/2-inch) roof sheathing for plywood or 7/16-inch for OSB in most residential applications with standard 24-inch on-center truss spacing. In higher wind zones and for tile roof applications, the minimum often increases to 19/32-inch or 5/8-inch. Always verify with your local Pinellas County building department, as requirements vary by wind zone and building configuration.

How much does roof decking replacement cost in Pinellas County?

Roof decking replacement in Pinellas County typically costs $70-100 per sheet installed for CDX plywood and $50-80 per sheet installed for OSB. For a full decking replacement on a 2,000 square foot roof, expect to add $3,000-6,000 to your roofing project. Partial replacement (the more common scenario) involves 5-20 sheets and adds $375-2,000 to the project cost.

Can you install a new roof over damaged decking?

No. Florida building code requires all damaged, rotted, or delaminated decking to be replaced before new roofing material is installed. A qualified contractor will inspect every sheet after tear-off and replace compromised panels. Installing over damaged decking is a code violation, voids your warranty, and creates a dangerous structural weakness during hurricanes.

Does OSB swell when it gets wet?

Yes. OSB is highly susceptible to permanent edge swelling when exposed to moisture. The wood strands at cut edges absorb water and swell 15-25% in thickness, creating visible ridges that show through shingles. This swelling is largely permanent. In Florida's humid environment with frequent thunderstorms, this is a significant concern that does not exist with plywood decking.