Plywood Veneer Grade Standards (PS 1-09)
Grade StandardVeneer grade classifications for structural and appearance plywood per the U.S. Voluntary Product Standard PS 1-09. Covers face/back veneer grades A through D, exposure durability classifications, and group numbers.
Veneer Grade Classifications
Source: NIST PS 1-09 — Structural Plywood| Grade | Description | Allowable Defects | Typical Use |
|---|---|---|---|
| A | Smooth, paintable face | Neatly made repairs permitted; no knots or open defects | Cabinet panels, furniture, architectural |
| B | Solid surface | Small circular repairs, tight knots up to 1", minor splits | Underlayment, cabinet backs, concrete forms |
| C Plugged | Improved C grade | Synthetic repairs, limited knotholes up to 1/4" × 1/2" | Underlayment, tile backing |
| C | Minimum exterior face | Knotholes up to 1-1/2", limited splits, synthetic repairs | Exterior sheathing, CDX plywood face/back |
| D | Interior only | Knotholes up to 2-1/2", limited white pocket, stitching permitted | Interior sheathing, CDX plywood back |
Exposure Durability Classifications
Source: NIST PS 1-09 — Structural Plywood| Classification | Adhesive Type | Moisture Tolerance | Typical Products |
|---|---|---|---|
| Exterior | Waterproof (phenolic) | Permanent weather exposure | Marine plywood, MDO/HDO, siding |
| Exposure 1 | Waterproof (phenolic) | Temporary construction exposure; not permanent | CDX, structural sheathing |
| Exposure 2 | Intermediate (melamine) | Brief, protected moisture exposure only | Some interior panels |
| Interior | Moisture-resistant (urea) | Dry conditions only | Interior finishing, furniture |
Applicable Codes & Standards
- • NIST PS 1-09 — Structural Plywood (U.S. Voluntary Product Standard)
- • APA — The Engineered Wood Association grading guidelines
- • IRC Chapter 5 — Floors (R503.2.1 subflooring)
- • IRC Chapter 6 — Wall construction (R602.10 bracing)
- • IRC Chapter 8 — Roof-ceiling construction (R803.2.1)
- • PS 2-18 — Performance Standard for Wood Structural Panels
How to Read Plywood Grade Stamps
Every APA-rated plywood panel carries a grade stamp on one face or edge. The stamp includes the panel grade (e.g., "C-D"), the exposure durability classification (e.g., "Exposure 1"), the span rating (if structural), the mill number, and the APA certification mark.
For example, a panel stamped "C-D EXPOSURE 1 APA 32/16" is a structural plywood with C-grade face veneer, D-grade back veneer, Exposure 1 adhesive (waterproof but rated for temporary construction moisture only), and a 32/16 span rating (32" roof span, 16" floor span).
Important Distinction: Exposure vs. Grade
The exposure classification describes the adhesive bond — how well the glue resists moisture. The veneer grade describes the wood surface quality. A panel can have excellent adhesive (Exterior) with rough veneers (C-D), or poor adhesive (Interior) with beautiful veneers (A-A). These are independent properties.
"CDX" plywood — the most commonly referenced grade in construction — actually means C-grade face, D-grade back, with Exposure 1 adhesive. The "X" is an industry convention for "Exposure 1" (not "Exterior"), though the waterproof adhesive in Exposure 1 is identical to Exterior-rated adhesive.