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Roof deck

Plywood vs OSB Roof Decking: Thickness, Nailing and What Florida Code Says

For roof decking, plywood and OSB are rated the same way and both meet code. The APA says its rated sheathing works equally well under shingle or tile. Thickness, ring shank nailing and the deck's condition matter more than which one you have.

By Josh Hildebrand, owner of Coastline Roofing · Florida license CCC1331076 ·

You may be wondering which is better, plywood or OSB, and what the roofer means by replacing decking. The short version is below, with the Florida details.

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The basics

What is roof decking, and what is it made of?

Roof decking, also called sheathing, is the layer of wood panels nailed to the rafters or trusses. The shingles, tile or metal go on top of it.

Most Florida homes built in the past few decades have a deck of plywood or OSB. Plywood is made of thin layers of wood glued together. OSB, short for oriented strand board, is made of wood strands pressed and glued into a panel. Older homes may have a deck of wood planks instead.

The deck does three jobs. It holds the roof covering. It carries the load of people and weather. And in a hurricane it resists uplift, which is wind trying to pull the roof off. How well the panels are nailed to the framing matters as much as what they are made of.

Who this affects: anyone getting a new roof, because the deck is checked whenever the old roof comes off. Who decides: the roofer, within the building code. When it comes up: at tear-off, when the old shingles are gone and the deck shows. Where: Florida, where the code sets nailing and thickness for high winds. This page covers the choice between plywood and OSB, and how thick and how tightly nailed the deck should be.

Wondering what shape your roof deck is in?

Coastline does roof replacement on shingle, tile and metal roofs and repairs decking when the roof comes off. A written photo report shows what the deck looks like. Coastline Roofing works all over Florida (license CCC1331076).

Call (941) 896-7793 or text your town and a photo.

The comparison

Plywood vs OSB roof decking: which is better?

For roof decks, both are rated the same way and both meet code. The APA says its rated sheathing works equally well under shingles and tile.

The APA, the engineered wood trade group that rates both products, says APA Rated Sheathing is equally effective under built-up roofing, asphalt or fiberglass shingles, tile roofing or wood shingles. Plywood and OSB carry the same span rating system, so a 7/16 inch panel is a 24/16 whether it is plywood or OSB.

Plywood and OSB roof sheathing compared
FeaturePlywoodOSB
How it is madeThin wood layers glued togetherWood strands pressed and glued
Span rating systemAPA rating, such as 24/16 or 32/16Same APA rating system
Nailing scheduleSame schedule for the thicknessSame schedule for the thickness
Gap between panelsAbout 1/8 inch at edges and endsAbout 1/8 inch at edges and ends
Wet weatherCover it with underlayment soon and protect the edgesCover it with underlayment soon and protect the edges
Walking surfaceNo special sidePut the skid-resistant side up on pitched roofs
Model code minimum, 24 inch framing15/32 inch7/16 inch
CodeAllowedAllowed

One real difference shows up in the model residential code (IRC 2018): for rafters or trusses 24 inches apart, the minimum is 7/16 inch OSB or 15/32 inch plywood. Both carry a 24/16 span rating, and the panel must be rated Exposure 1 or Exterior. Florida's wind rules, covered below, can require thicker panels than either.

The honest answer is that the installation matters more than the product. The APA says to cover sheathing as soon as possible with underlayment to protect it from excess moisture, and to protect panel edges from weather. A deck that sat wet for weeks, was nailed too far apart or has panels butted tight will give problems either way.

If you have OSB and heard it is weaker, the APA's rating treats it the same. If you have plywood and heard it is old-fashioned, the same is true. What you want to know is thickness, condition and nailing. The sections below cover each.

Thickness

How thick should roof decking be in Florida?

Under the 2020 Florida Building Code, thickness goes up with wind speed and exposure. For 24 inch spacing, 7/16 is the lowest and 19/32 is common in open terrain.

The APA's rating chart sets the basics. A 7/16 inch panel (24/16) can span 24 inches between supports. A 15/32 inch panel (32/16) spans 32 inches with edge support or 28 inches without. A 19/32 inch panel (40/20) spans 40 inches with edge support. The APA notes that trusses 24 inches apart are widely used for residential roofs, so 24 inch spacing is the usual case.

Florida adds a wind rule. A summary of the 7th Edition (2020) Florida Building Code, Residential, Table R803.2.2, gives the minimum thickness for 24 inch framing by wind speed and exposure. The exposure letters describe how open the terrain around the house is, and C and D are the more open categories.

Minimum roof sheathing thickness, 24 inch framing (excerpt, 2020 Florida Building Code, Residential)
Exposure140 mph150 mph160 mph
B7/16 (24/16)15/32 (32/16)19/32 (40/20)
C19/32 (40/20)19/32 (40/20)19/32 (40/20)
D19/32 (40/20)19/32 (40/20)19/32 (40/20)

This is an excerpt from a county summary of the 2020 edition. Florida updates the code on a cycle, so your permit is judged under the edition in force when it is pulled. Your building department and roofer can tell you which number applies to your house.

For many Gulf Coast homes that means 19/32 inch or thicker is the safe assumption in an exposed location. To see how your county handles wind speed and permits, read the Florida Building Code and roofing.

Nailing

How should roof decking be nailed under Florida code?

With ring shank nails, spaced tightly. The nail size depends on the panel thickness, and the spacing depends on wind speed and exposure.

Smooth nails can back out under uplift. Ring shank nails have rings that grip the wood. The 2020 Florida Building Code summary says ring shank nails are required, and sets the size by panel thickness:

  • For panels 15/32 inch or thinner: ASTM F1667 RSRS-01 nails, 2 3/8 inches long and 0.113 inch thick.
  • For panels thicker than 15/32 inch: RSRS-03 nails (2 1/2 inches, 0.131 inch) or RSRS-04 nails (3 inches, 0.120 inch).

Table R803.2.3.1 then sets the maximum spacing by wind speed, exposure and the density of the framing lumber. In the excerpt we reviewed, spacing ranges from 6 inches down to 3 inches. The model code baseline is lighter. The IRC calls for 8d common nails (0.131 inch, 2 1/2 inches long) every 6 inches at panel edges and 12 inches in the field, and notes that coastal areas, including parts of Florida, may need tighter spacing such as 4 inches and 8 inches. The APA's own baseline matches it: 8d nails every 6 inches along panel edges and every 12 inches on the inside supports, and it says tighter schedules may be needed in high wind zones.

The Florida Division of Emergency Management goes further for a reroof. It says the common nail sizes and spacing found in many older plywood and OSB decks often do not give enough uplift resistance, staples perform poorly at any spacing, and the ideal is 8d ring shank nails at 6 inch spacing along panel edges and framing. For roofs designed for winds over 120 mph, it recommends adding ring shank nails at 6 inches along the framing across the whole roof. Read more in our roof nailing guide, and see wind mitigation and the roof deck for how deck attachment is checked.

Condition

What makes a roof deck bad enough to replace?

Most decks can be reused if they are sound. These are the problems that call for new panels or more nails.

Rot

Wet wood that has gone soft has lost strength. The Florida Division of Emergency Management says rotted sections should be replaced with panels of the same thickness.

Delamination

Plywood layers or OSB faces can separate after repeated wetting. The state guide lists delaminated panels as ones to replace.

Warping

A panel that has bowed or warped sits unevenly under the shingles and can pull on its nails. Warped sections are on the same replace list.

Missing or weak nails

The state guide says some panels are under-nailed or missing nails, and that the code now asks for sheathing to meet current fastening standards before new shingles go on. A roofer checks every sheet.

Staples

Staples perform poorly no matter how closely they are spaced, so a deck held by staples needs ring shank nails added.

An old plank deck

Planks are judged differently. The state guide says existing nailing is usually fine if at least two nails were driven wherever a plank crosses a rafter or truss.

The process

What happens to the roof deck when a roof is replaced?

The old roof comes off, the deck is checked panel by panel, damaged panels are replaced, and the rest is nailed to the current standard before new roofing goes on.

A deck cannot be judged until the old roof is gone. That is why a quote often says "decking replaced as needed." Our page on tear-off surprises explains what that means in practice.

  1. Tear off the old roof

    Remove the old shingles and underlayment so the deck is bare. A roof laid over old shingles hides the deck. Read why in roof over existing shingles.

  2. Inspect every sheet

    Look for rot, delamination, warping and missing nails. Photographs of bad spots are part of a good report.

  3. Replace damaged panels

    The Florida Division of Emergency Management says to replace them with the same thickness so the roof surface stays flat.

  4. Add nails

    Add ring shank nails where the existing nailing falls short of the code or the roof's design wind speed.

  5. Check gaps and edges

    Leave about 1/8 inch at panel joints, and use clips or blocking where the APA table calls for edge support.

  6. Cover the deck

    Install underlayment quickly to protect the deck from rain. See roof deck damage for what water does to a deck.

Coastline does this on shingle, tile and metal roofs. On mobile homes, Josh checks the wiring first because the trusses are thin, then tears the roof off to the decking and repairs the decking. See mobile home roofing. Josh reviews every job, and a written photo report shows the deck before new roofing covers it. For the full job, see roof replacement and what to expect.

Reviews

What homeowners say about working with Coastline

★★★★★
"From beginning to end the roof was done in 2 days. One night the crew stayed until 8:00. Each evening before leaving the crew ensured the yard was cleaned. We are so happy, and our roof is beautiful!"
Sharon T.Roof replacement
★★★★★
"Russell was great to work with. He was prompt in coming out to assess our roof and very knowledgeable. ... The job was complete in 2 days once work began."
Bryan S.Roof replacement
★★★★★
"Josh was especially amazing. He was professional, patient, and took the time to explain everything clearly so I felt comfortable and informed throughout the entire process. You can tell he genuinely cares about his customers and takes pride in his work."
Madison T.Roofing customer
Keep reading

Related guides

Roof Replacement

Tear-off, deck check and a new roof, with a written photo report.

See our roof replacement →

Roof Deck Damage

What water does to the wood under your roof.

Read the guide →

Roof Nailing Requirements in Florida

Nail types and spacing, explained.

Read the guide →

Also see Florida Building Code roofing rules and tear-off surprises.

FAQ

More questions

Is OSB or plywood better for a roof?

The APA rates both the same way and says its rated sheathing is equally effective under shingles and tile. The deck's thickness, nailing and condition matter more. Cover the deck quickly after install and protect panel edges from rain. Follow the panel maker's instructions and the Florida code.

What thickness of plywood is required for a roof in Florida?

It depends on wind speed and exposure. The 2020 code summary lists 7/16 inch for 140 mph in Exposure B with 24 inch framing, 15/32 at 150 mph, and 19/32 inch for higher winds and for Exposures C and D. Check which edition applies to your permit.

Do I need ring shank nails on my roof deck?

Yes, the Florida Building Code summary says ring shank nails are required, with the size set by panel thickness. The state's reroof guide says 8d ring shank nails at 6 inches along panel edges and framing is the ideal, and recommends adding them across the roof in high wind areas.

Can a roofer reuse my old roof deck?

Often yes, if it is sound and meets current nailing standards. Rotted, delaminated or warped panels are replaced with the same thickness, and weak nailing is upgraded with ring shank nails, per the Florida Division of Emergency Management. The deck can only be judged after tear-off.

Why do the panels have a gap between them?

The APA recommends about 1/8 inch at edges and end joints. Wood panels swell and shrink with moisture, and the gap gives room so they do not buckle. Panel clips or blocking support the unsupported edges between rafters.

What is a panel clip, and do I need them?

A panel clip is a small metal piece that fits between two roof panels where they meet between rafters. It supports the edges and keeps the gap even. The APA says to use one clip per span, or two for spans of 48 inches or more, when edge support is required. The thickness and span rating decide whether it is.

Sources

  1. APA The Engineered Wood Association: Roof Construction, excerpt of the Engineered Wood Construction Guide (Form E30W, 2016)
  2. Columbia County, Florida Building Department: Significant Changes to Roofing Requirements, 7th Edition (2020) Florida Building Code
  3. Florida Division of Emergency Management: Residential Retrofit Guide, Re-roofing soon
  4. APA The Engineered Wood Association: Roofs, Engineered Wood Construction Guide (Form E30, 2020)
  5. Jaspector: Roof sheathing thickness, IRC 2018 Chapter 8
  6. Jaspector: Roof sheathing fastening, IRC 2018 Chapter 8

Want to know what is under your shingles?

Josh will inspect the roof and send a written photo report. If the deck needs work, you will see where and why before anything is covered.

Call (941) 896-7793 Text (941) 345-0072
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