Roof Sheathing Thickness and Size: What to Use
Quick answer: Roof decking thickness cannot be selected from a single universal number. Check the panel grade and span rating, framing spacing, loads, edge support, adopted code and roof-covering requirements together. Four-by-eight-foot panels are common, but a thickness or span stamp alone does not approve a particular roof assembly.
Key takeaways
- Panel size is standard (4 by 8 feet); thickness is chosen by framing spacing, loads and roof covering.
- The span rating stamped on each panel is the real test, not thickness alone.
- OSB and plywood are both accepted for roof decking; board sheathing works only if it is solid and sound.
- Spaced plank sheathing under old wood shingles must be covered or replaced before asphalt shingles go on.
- Shingle manufacturers, including GAF, publish deck requirements; meeting them protects the warranty.
How thick should roof sheathing be?
Use the thickness specified for the roof’s actual design and covering. Two panels of similar thickness can have different ratings, and a familiar nominal thickness does not establish the required fastening or edge support.
Collect the framing spacing, existing panel stamp, panel condition and proposed roof covering. Have the contractor or designer identify the applicable load/span guidance and any manufacturer minimum. If the roof changes to a heavier covering, check the structure as well as the sheathing; adding thicker panels is not a substitute for verifying the framing.
For repair work, match the required specification and maintain a suitable surface across panel transitions. Simply choosing the thinnest available sheet, or matching damaged material without checking its suitability, can repeat an existing problem.
Standard roof sheathing thickness and panel size
APA’s Rated Sheathing data sheet lists common performance categories and corresponding span ratings. It describes a typical panel size of 4 by 8 feet while noting that other sizes exist.
| Performance category | Example APA span rating |
|---|---|
| 3/8 | 24/0 |
| 7/16 | 24/16 |
| 15/32 | 32/16 |
| 19/32 | 40/20 |
| 23/32 | 48/24 |
This is a label-reading reference, not a specification authorizing those spans on your house. Use the actual stamp and the applicable load/span tables, installation orientation, edge-support provisions and roof-covering instructions. Ask the designer or contractor to resolve conflicting requirements before ordering.
APA installation guidance recommends panel joint spacing, generally 1/8 inch unless the manufacturer directs otherwise. Edge clips are not universally required or universally sufficient; the assembly determines the necessary edge support. A roof panel should not be selected on thickness alone.
What type of sheathing to use for a roof
For most homes, the type of sheathing to use for a roof is rated OSB or plywood roof sheathing whose span rating matches the framing. Either material works when the grade, thickness and installation are right; the choice usually comes down to cost, availability and preference.
What is used for roof sheathing today:
- OSB is an engineered wood panel option; use the actual rating and specification.
- Plywood is another structural panel option; its grade and condition matter as well as thickness.
- Radiant barrier panels are OSB or plywood with a foil face, popular in hot climates. See roofing material options.
- Board sheathing is used mostly when repairing an existing board deck.
If you want a broader view of what goes on top of the deck, our roofing materials page covers shingle and metal options.
OSB vs plywood vs board sheathing
OSB and plywood can both be rated structural sheathing. Compare the actual grade, performance category, span rating and installation instructions. Existing board decking needs assessment for condition, width, gaps and compatibility with the proposed covering.
| Question | Why it matters |
|---|---|
| Is the panel rated for this application? | Material name alone does not establish capacity |
| Does the stamp suit the design? | Framing spacing and loads influence selection |
| Is the panel damaged or swollen? | A suitable specification cannot make damaged material sound |
| What support and fastening are required? | The installed assembly, not just the sheet, carries loads |
| Does the covering accept the deck? | Structural suitability and covering compatibility are separate checks |
Do not choose plywood or OSB from a blanket claim that one always holds nails better or withstands water better. Match the rated product to the application, protect it during construction and investigate recurring moisture rather than covering it over.
Plank and solid sheathing on older homes
Roof plank sheathing is solid lumber boards nailed across the rafters, common on homes built before plywood and OSB panels took over. Roof board sheathing can be laid tight (solid sheathing) or with gaps between boards (spaced sheathing).
- Solid sheathing means the boards are fitted together without significant gaps. If the boards are sound, flat and within the shingle maker's width and gap limits, shingles can often go over them.
- Spaced sheathing was used under wood shingles and shakes so they could breathe. Asphalt shingles cannot be nailed over gaps, so the roof needs new panels laid over the boards or the boards replaced.
Roof sheathing boards also have problems panels do not: they shrink and cup over decades, knots fall out, and old nails pull loose. A qualified crew should assess exposed decking using safe access methods and document split, rotted or loose boards.
Water-resistant roof sheathing options
Water-resistant roof sheathing usually means a panel with a factory-applied water-resistive overlay, which can replace or work with underlayment depending on the product's listing and the code your city has adopted. Some products use taped seams to form the water barrier.
Points to know:
- Standard OSB and plywood are rated for exposure during construction, not permanent wetting.
- Integrated-barrier panels must be installed and taped exactly as the manufacturer specifies, and the shingle manufacturer must accept them for the warranty.
- Determine whether separate underlayment is required or permitted for the specific integrated-panel and covering assembly.
Shingle manufacturer decking requirements
Shingle manufacturers require a solid, dry, flat deck that meets minimum panel thickness and span rules, and they publish those rules in their installation instructions. GAF decking requirements, for example, appear in each shingle line's application instructions and warranty documents; Malarkey, IKO, Owens Corning and Atlas publish their own.
Typical points in these requirements:
- The exact product’s minimum deck specification, checked against the structural design and adopted code.
- Panels installed with the panel maker's spacing and support or clip requirements.
- Board decking limited to a maximum width and gap between boards, with sound, well-nailed boards.
- A deck that is dry and free of loose, damaged or warped areas before underlayment.
Exact figures change between editions, so check the current instructions for the shingle you plan to use. Installing over a deck that does not meet them can affect warranty coverage.
Central Texas considerations: older Austin homes and re-roofs
In Central Texas, the decking question comes up most on older homes and on roofs that have leaked. Homes in older Austin neighborhoods may still have board sheathing, sometimes spaced from the original wood shingles. Do not infer the panel thickness or condition from a neighborhood or construction date; check the existing assembly.
On a re-roof, expect the roofer to:
- Inspect the deck after tear-off and mark damaged areas.
- Replace rotted or delaminated panels to match the surrounding thickness.
- Recommend full re-decking over spaced boards.
- Have inadequate support or deflection assessed before choosing a repair detail.
Permits and the code edition in force vary by city; confirm requirements with your city's building department. Our roof replacement page explains how we handle decking during a project, and the roof replacement planning covers the basics.
Frequently asked questions
What size is roof sheathing?
Four-by-eight-foot panels are common, although other sizes exist. Panel dimensions describe the sheet, while thickness, grade and span rating help determine its structural application. Confirm those properties along with framing spacing, loads and the covering’s requirements. Older board decks need their own condition and compatibility assessment.
Is 7/16 OSB OK for roof sheathing?
It may be suitable for a particular assembly, but thickness alone is insufficient. Check the actual panel rating against framing spacing, design loads, installation orientation, edge support and the roof-covering instructions. Use the approved specification for your roof rather than assuming every 7/16-inch sheet is interchangeable or adequate.
Can shingles go over plank sheathing?
Sometimes. Asphalt shingles need a solid deck, so tightly fitted, sound boards can work if they meet the shingle manufacturer's limits on board width, gaps and condition. Spaced boards left from old wood shingle roofs do not qualify. In that case new panels are installed over or in place of the boards before re-roofing.
What decking do shingle manufacturers require?
Shingle manufacturers generally require a solid, dry, flat deck of plywood, OSB or tight-fitting boards that meets minimum thickness and span rules, with panels gapped and supported per the panel maker's instructions. Exact minimums vary by brand and are published in the installation instructions and warranty documents, including GAF's, so check the current version for your shingle line.
Find out what's under your shingles
Decking is the part of a roof you cannot see from the ground. Request a free roof inspection with photo documentation and ask which deck areas are accessible and which remain concealed. For a material-by-material cost range, use the roof calculator, or call (512) 910-4110.