Roof sheathing thickness is set by the panel's span rating and the rafter or truss spacing, not by thickness alone. Under 2021 IRC Table R503.2.1.1(1), a 24/16 panel (7/16 inch) is listed for spans up to 24 inches, a 32/16 panel (15/32 or 1/2 inch) up to 32 inches with edge support, and a 40/20 panel (19/32 or 5/8 inch) up to 40 inches.
The table is shared with subfloor sheathing, so this article reads only the roof side of it. The code edition your jurisdiction has adopted, plus any local amendments, governs. Manufactured roof trusses come with their own design drawings, and engineered panels or structural insulated products follow the manufacturer's tables and instructions. For the rafters or trusses underneath, see the rafter span chart and rafters vs trusses.
How to read a roof sheathing span rating
Panels are graded under DOC PS 1, DOC PS 2, CSA O325 or CSA O437 and must carry a grade mark or certificate of inspection showing grade, bond classification and performance category (2021 IRC Section R803.2.1). The performance category is the code's "nominal panel thickness." On the stamp you will see a pair of numbers such as 32/16.
- The first number is the maximum rafter or truss spacing, in inches, for roof use.
- The second number is the maximum joist spacing for subfloor use.
That is why a 24/0 panel is a roof-only rating: the 0 means it has no subfloor span. Plywood and OSB are both wood structural panels, and the table does not treat them differently. A plywood panel and an OSB panel with the same span rating, grade and performance category are read from the same row.
Roof sheathing span chart (2021 IRC Table R503.2.1.1(1))
2021 IRC Table R503.2.1.1(1), roof columns for sheathing grades. Panels continuous over two or more spans, strength axis perpendicular to supports. Total loads based on a 10 psf dead load. "None" means the table lists no value.
| Span rating | Nominal panel thickness (inch) | Live load at 16" o.c. (psf) | Live load at 24" o.c. (psf) | Max span with edge support (inches) | Max span without edge support (inches) | Roof total load (psf) | Roof live load (psf) |
|---|---|---|---|---|---|---|---|
| 16/0 | 3/8 | 30 | none | 16 | 16 | 40 | 30 |
| 20/0 | 3/8 | 50 | none | 20 | 20 | 40 | 30 |
| 24/0 | 3/8 | 100 | 30 | 24 | 20 | 40 | 30 |
| 24/16 | 7/16 | 100 | 40 | 24 | 24 | 50 | 40 |
| 32/16 | 15/32 or 1/2 | 180 | 70 | 32 | 28 | 40 | 30 |
| 40/20 | 19/32 or 5/8 | 305 | 130 | 40 | 32 | 40 | 30 |
| 48/24 | 23/32 or 3/4 | none | 175 | 48 | 36 | 45 | 35 |
| 60/32 | 7/8 | none | 305 | 60 | 48 | 45 | 35 |
The table also carries a column for subfloor spans and a separate group of rows for combination subfloor underlayment. Those are floor products and are left out here. Read the footnotes in the code before using any cell, because the table attaches a footnote to the 20 inch value in the 24/0 row.
What the footnotes change
- Dead load. Total loads assume a 10 psf dead load. If the roof dead load is higher, the live load must be reduced accordingly (footnote a).
- Deflection. The uniform load limits are 1/180 of the span under live plus dead load and 1/240 of the span under live load only (footnote f).
- Panel width. The table applies to panels 24 inches or wider (footnote c).
- Concentrated loads. Spans are held to the listed values because of the possible effect of concentrated loads (footnote b).
- The 16 and 24 inch columns. These live load values come from APA E30, and the code points to that standard for spans not listed (footnote l and Section R803.2.2).
Roof sheathing thickness at 16 inches on center
Every rating from 16/0 up to 40/20 has a live load value at 16 inches on center. At that spacing a 3/8 inch 24/0 panel is listed at 100 psf, a 7/16 inch 24/16 panel at 100 psf, and a 15/32 or 1/2 inch 32/16 panel at 180 psf. Because the span rating limits the spacing, a 16/0 panel is only good to 16 inches, so it fits 16 inch framing and nothing wider.
Typical trusses and common rafter layouts at 16 inches therefore have a wide choice of panels. The practical constraints are usually the roofing manufacturer's minimum deck requirements, the expected snow load, and how far the panel is walked on during construction. None of that is in this table.
Roof sheathing thickness at 24 inches on center
At 24 inches the choice narrows. Panels rated 16/0 and 20/0 have no 24 inch value, and their maximum span is 16 and 20 inches. Starting at 24/0, the table lists 30 psf at 24 inches. A 24/16 panel (7/16 inch) is listed at 40 psf, a 32/16 panel (15/32 or 1/2 inch) at 70 psf, and a 40/20 panel (19/32 or 5/8 inch) at 130 psf.
If the live load on your roof is higher than the 24 inch value for a panel, either move to a heavier rating or reduce the framing spacing. Check the design snow load in your jurisdiction against the panel's live load column. The roof framing plan guide shows where the framing spacing is stated on the drawing, and roof truss types covers the framing that sets that spacing.
Edge support: when roof panels need blocking or clips
The table gives two maximum spans, one with edge support and one without. Footnote d defines edge support as lumber blocking, panel edge clips, tongue-and-groove panel edges, or another approved type. Clips are placed one midway between each support, except two equally spaced between supports where the span is 48 inches.
The difference is real at wider spans. A 32/16 panel is listed at 32 inches with edge support and 28 inches without. A 40/20 panel is listed at 40 inches with edge support and 32 inches without. At 24 inch framing, a 24/16 panel or heavier reaches 24 inches whether or not the edges are supported. A 24/0 panel drops to 20 inches without edge support.
Table R602.3(1) footnote h adds that blocking of roof panel edges perpendicular to the framing is not required except as other provisions of the code require it. Where the framing spacing is close to a panel's no-edge-support limit, plan for clips, blocking or tongue-and-groove edges, or size the panel from the no-edge-support column.
Lumber board roof sheathing
Boards are still allowed. Section R803.1 sends lumber sheathing to Table R803.1.
2021 IRC Table R803.1, minimum net thickness of lumber roof sheathing.
| Rafter or beam spacing (inches) | Minimum net thickness (inches) | Footnote |
|---|---|---|
| 24 | 5/8 | none |
| 48 | 1-1/2 tongue and groove | Minimum 270Fb, 340,000E |
| 60 | 1-1/2 tongue and groove | Minimum 420Fb, 660,000E |
| 72 | 1-1/2 tongue and groove | Minimum 600Fb, 1,150,000E |
Spaced lumber sheathing under wood shingles and shakes follows Sections R905.7 and R905.8, and spaced sheathing is not allowed in Seismic Design Category D2. For fastening boards, Table R602.3(1) lists a 1x6 board with 3-8d box nails, 2-8d common nails, 2-10d box nails or 2 staples at each bearing. Wider boards need more fasteners, so read items 20 and 21 of that table.
Roof sheathing nailing schedule
The nail sizes and spacings come from Table R602.3(1), as Section R803.2.3 requires. Roof panels also follow the joint pattern in that table or in APA E30, with joints staggered or not staggered.
2021 IRC Table R602.3(1), wood structural panel roof sheathing to framing. Spacing in inches.
| Panel thickness | Fastener | Edges | Intermediate supports |
|---|---|---|---|
| 3/8 to 1/2 inch | 8d common (2-1/2" x 0.131") or RSRS-01 ring shank (2-3/8" x 0.113") | 6 | 6 |
| 19/32 to 3/4 inch | 8d common (2-1/2" x 0.131") or RSRS-01 ring shank (2-3/8" x 0.113") | 6 | 6 |
| 7/8 to 1-1/4 inch | 10d common (3" x 0.148") or deformed nail (2-1/2" x 0.131" x 0.281" head) | 6 | 12 |
Three footnotes matter on a roof:
- Wind zones. For roof panels attached to gable end framing and to intermediate supports within 48 inches of roof edges and ridges, nails go at 4 inches on center where the ultimate design wind speed is greater than 130 mph in Exposure B or greater than 110 mph in Exposure C (footnote f).
- Long spans. Nails must be at no more than 6 inches on center at all supports where spans are 48 inches or greater (footnote c).
- Edge nailing. The edge spacing applies to panel edges supported by framing members and required blocking (footnote h).
RSRS-01 is a roof sheathing ring shank nail meeting ASTM F1667 (footnote b). Nails of other materials, such as stainless steel, are designed by accepted engineering practice or approved under the code's alternative methods section.
Exposure rating and gable overhang limit
Panels left permanently exposed outdoors must have an exterior exposure durability. Roof panels exposed on the underside, as at an open eave soffit, may be interior type bonded with exterior glue, identified as Exposure 1 (Section R803.2.1.1). Fire-retardant-treated plywood has its own allowable stress requirements under Section R803.2.1.2.
At the gable end, Section R803.2.3 says panels complying with Table R503.2.1.1(1) may not cantilever more than 9 inches beyond the gable endwall unless supported by gable overhang framing. A wider rake overhang needs outlookers or another framed overhang. Gable and hip roof framing shows where that framing sits, and roof pitch and slope covers how pitch is drawn on the plan.
Using the table on a roof plan
Put the sheathing on the drawing as a general note, not as an afterthought: panel span rating, thickness, exposure rating, edge support method, and fastener schedule, with the table numbers beside them. For example, a note might read "7/16 in. 24/16 exposure 1 panels, edge clips at midspan, 8d common at 6 in. o.c." That lets a reviewer check the same table rows you used. A low-slope deck follows the same table, and the flat roof framing plan guide covers the drawing side of that.
Framing Plan is a preliminary drawing aid. It draws joist layouts, beams and openings and exports PNG, PDF and DXF. It does not check sheathing against the code, and the editor works in millimeters, so read the values here and write them on your plan. Open the framing studio to lay out the framing that the sheathing will sit on.