FreeWhat Is CDX Plywood? Meaning, Grades and Uses
CDX plywood is softwood construction plywood with a C-grade face, a D-grade back and glue rated Exposure 1, the “X”. That glue lets it stay wet during construction without delaminating, but it is not meant for permanent outdoor exposure. It is used for roof and wall sheathing and subfloors, where it is covered, and is not a furniture board.
Sizes and thicknesses
| Nominal | Actual thickness and use |
|---|---|
| 3/8 in | 11/32 in (8.7 mm): wall sheathing |
| 1/2 in | 15/32 in (11.9 mm): roof and wall sheathing |
| 5/8 in | 19/32 in (15.1 mm): roofs, subfloors on close joists |
| 3/4 in | 23/32 in (18.3 mm): subfloors, heavy shelving |
| Sheet sizes | 4 × 8 ft (most common), 4 × 9 and 4 × 10 ft |
Softwood plywood grades
| Grade | Face and back |
|---|---|
| AC / ACX | Sanded A face, C back: painted projects, shelving, sheds. |
| BC / BCX | B face, C back: utility projects with one decent face. |
| CDX | C face, D back, exposure glue: sheathing and subfloors. |
| Rated Sheathing | Performance-rated panels (plywood or OSB) with a span rating such as 32/16. |
| Sturd-I-Floor | Tongue-and-groove panels rated for single-layer floors. |
Advantages
- Cheap and widely available
- Stiff and strong for sheathing
- Holds nails and screws well
- Survives rain during construction
Drawbacks
- Rough faces with knots and plugs: not for visible work
- Core voids
- Not for permanent outdoor exposure
- Can splinter when cut
What it is used for
- Roof sheathing
- Wall sheathing
- Subfloors and underlayment
- Shop shelves, crates and jigs
Tips for working with CDX plywood
- Leave a 1/8 in (3 mm) gap between sheets on roofs and walls for expansion.
- Put the C face up or out.
- For a visible project, choose ACX or BCX instead: same glue, a sanded face.
- Cover or paint it if it will stay outside.
Frequently asked questions
Can CDX plywood be used for roofing?
Yes. CDX is the usual plywood for roofing and roof sheathing under shingles, typically 1/2 or 5/8 in over rafters at 24 in. It is not meant to stay exposed to the weather; pressure treated CDX plywood is used where the wood touches the ground or stays damp.
What does CDX stand for?
C is the grade of the face veneer, D the grade of the back, and X the Exposure 1 glue that tolerates moisture during construction.
Is CDX plywood waterproof?
No. Its glue survives getting wet during construction, but the plywood must be covered: left outside, the faces check and the layers can separate.
Can I use CDX plywood for a subfloor?
It is often used, but tongue-and-groove plywood rated for floors (Sturd-I-Floor) is better: the joints stay flush and it is thicker for its span.
What is the difference between ACX and CDX?
ACX has a sanded A face for painting and a C back, with the same exposure glue. Use ACX where one face is seen, CDX where both are hidden.
CDX plywood or OSB?
Both work for sheathing. Plywood is stiffer, holds fasteners better and recovers better from wetting; OSB is cheaper and more uniform, but its edges swell when wet. See OSB vs plywood.
Furniture plans to build
All plans →
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MDF vs PlywoodMDF vs plywood for cabinets, shelves and doors: strength, sag, screw holding, paint finish, moisture, weight and cost compared, with the right use for each.OSB vs PlywoodOSB vs plywood compared: strength, stiffness, moisture, weight and cost, and which is better for subfloors, roof and wall sheathing, shelving and furniture.