Construction plywood grades: how to read a plywood grade stamp, span rating and Performance Category

What are construction plywood grades?

Construction plywood grades identify a structural panel’s intended use, span rating, thickness category and moisture exposure class. The grade stamp also identifies the product standard, certification agency and mill. Buyers should match all of these fields to the project specification before accepting a panel for construction.

PS 1-22, published by NIST on 2 October 2023, is the voluntary US product standard for structural plywood.

PS 1-22 classifies structural plywood by four things:

1. Bond classification: Exposure 1 or Exterior.
2. Span rating: the support spacing the panel is rated for.
3. Performance Category: the nominal thickness group.
4. Grade: the veneer grades and construction, such as C-D, Structural I or Underlayment.

Face appearance comes last. A construction grade with an unsanded C face is often the right panel, because nobody sees it once the roof or floor is finished.

What do A, B, C and D veneer grades mean?

The four veneer letters run from A, a smooth paintable face, to D, a utility face with open knots. The first letter of a two-letter code is the face and the second is the back, so C-D is a C face over a D back.

CDX is the C-D code with an Exposure 1 bond. Hardwood plywood adds a back number: 1 is the best back and 4 the worst, so A1 is the premium cabinet grade and D4 the cheapest.

Grade changes the price. On a 3/4 inch 4 × 8 ft sheet at big-box stores in 2026, CDX runs about $30 to $50, and sanded AC or BC about $50 to $80. A buyer who needs structure but not looks stops paying for the A face.

How to read a plywood grade stamp, line by line

Section 7.5 of PS 1-22 lists what every conforming panel must be marked with. A typical sheathing stamp carries these lines; the table decodes each.

The bond class must be in the stamp itself. PS 1-22 requires any further wording about glue, such as premium claims or brand names, to sit apart from the agency’s mark. If you see “waterproof glue” inside the stamp area, it is not part of the grade.

What does a span rating like 32/16 or 24/16 mean?

The span rating is the maximum centre-to-centre spacing of supports, in inches, that the panel is rated for under normal loads. Sheathing carries two numbers: roof span over floor span.

By convention, a span of 20 stands for 19.2 inches. PS 1-22 assigns span ratings either by prescriptive rules on species, grade and thickness or by performance tests at an accredited testing laboratory. The local building code still sets the actual maximum span, so the rating is the panel’s limit, not a design.

What is CAT rated sheathing? Performance Category explained

CAT rated sheathing is sheathing labelled with its Performance Category, the nominal thickness group used by the US building codes. PS 1-22 allows the label as Performance Category, PERF CAT, CAT or Category, and requires the actual thickness in thousandths of an inch beside it.

Each category has a range. These are the PS 1-22 limits for unsanded and touch-sanded panels, based on a tolerance of ±0.8 mm (1/32 in):

Categories exist because panels are slightly thinner than their nominal inch size. A 15/32 panel is sold where a “half inch” is called for. The codes’ advisory minimum for wall sheathing is the 3/8 Performance Category.

Exposure 1 plywood meaning, and how it differs from Exterior

Exposure 1 means the panel’s bond resists moisture during construction but the panel is not made for permanent weather. Exterior means the panel takes repeated wetting and drying or long-term exposure.

Exposure 2 is an older interior-only bond classification with limited moisture resistance; it is not used for construction panels that may get wet on site, so choose Exposure 1 or Exterior.

CDX is the familiar trade name for a C-D panel with an Exposure 1 bond. The X tells you the glue is moisture-resistant, not that the panel can stay outdoors uncovered. Our guide to CDX vs ACX and BCX plywood goes through each trade name.

What does Structural I mean, and what is 15/32 Structural 1 plywood?

Structural I is the PS 1 grade for engineered uses where design properties matter: shear walls, diaphragms, structural components. All face, back and inner plies must be Group 1 species, the strongest species group in the standard.

PS 1-22 allows Structural I in C-D, C-D Plugged, Underlayment and any Exterior grade, with extra limits: no white pocket in D veneers beyond set sizes, sound tight knots in D grade no larger than 63.5 mm (2-1/2 in), and plugs no wider than 102 mm (4 in).

So “15/32 Structural 1 plywood” is a panel in the 15/32 Performance Category, about 11.1–12.7 mm thick unsanded, graded Structural I, usually with a 32/16 span rating and an Exposure 1 bond. Engineers specify it for braced and shear walls because its design values are higher than ordinary rated sheathing.

Construction plywood ratings chart: which grade for which job

Use this plywood ratings chart to match the stamp to the job. It lists the common US construction grades.

Appearance grades such as A-A or B-B also exist under PS 1, but builders rarely pay for them on structure. For a full guide to the letters themselves, see plywood grades explained.

What are plywood species groups?

Species groups rank the timbers allowed in PS 1 plywood by strength and stiffness, from Group 1 (strongest) to Group 5. The group number appears on panels without a span rating.

• Group 1: dense species such as Douglas-fir from the coast and southern pines.
• Groups 2 to 4: progressively lighter species.
• Group 5: the lightest listed species.

Span-rated sheathing usually shows the span rating instead of a group number. Marine and Structural I panels are restricted to Group 1 species, and PS 1-22 Marine further limits faces and plies to Douglas-fir and Western Larch.

Plywood markings beyond the US: CE, EN 636 and AS/NZS 2269

Other markets mark construction plywood under their own systems, and a PS 1 stamp means nothing to a European or Australian inspector.

EN 13986 covers wood-based panels used in construction in Europe; CE marking itself comes from the EU Construction Products Regulation. Its plywood classes come from EN 636: EN 636-1 for dry conditions, EN 636-2 for humid conditions and EN 636-3 for exterior conditions. Ask your supplier which system the job’s inspector uses before you compare quotes.

What can an imported construction panel carry?

An imported panel can carry a PS 1 grade stamp only if its mill is certified for that product by an accredited certification agency. Without that, the honest marking is the panel’s own specification, not a copied stamp.

When a quote mentions a grade stamp, ask for three things:

1. The agency that certifies the mill for PS 1.
2. The mill number that will appear in the stamp.
3. The product specification the agency holds for that panel.

PS 1-22 also says that panels that fail must lose the stamp: rejected panels get a “REJECT – All other agency marks void” mark, and shop-cutting panels a 102 × 127 mm mark reading “Shop-cutting panel — all other agency marks void”. A sheet with a full grade stamp and visible faults outside its grade has missed that step.

Minh Thanh Plywood does not stamp panels to PS 1. We make construction and exterior plywood to the buyer’s written specification, and the order papers say exactly what the panel is.

Construction plywood from Vietnam: film-faced, anti-slip and exterior

In Vietnam, “construction plywood” means three main products: film-faced formwork panels, anti-slip platform panels and exterior or CDX-type sheathing panels. They are specified by bond, core, face and tolerance rather than by a US grade stamp.

Film weight is the main grade line for formwork panels: about 120–135 g/m² for standard film, from 135 g/m² for premium, and about 220 g/m² for anti-slip film with a wire-mesh or hexagon pattern. Our anti-slip plywood is made on order. For formwork pricing, see film-faced plywood price, and for all three lines, our construction plywood range.

How to check construction plywood on arrival

Check stamps, thickness and moisture on a sample of sheets from several packs before the panels go to site.

1. Stamp: every sheet carries the same grade, span rating, category, bond class, standard and mill number as the order.
2. Thickness: measure mid-length on all four edges and average the readings; compare with the Performance Category range.
3. Size: under PS 1-22, length and width may be up to 1.6 mm under the stated size, or 3.2 mm when marked sized for spacing, and never over.
4. Squareness: within 1.3 mm per metre of the longest edge, measured on the diagonals.
5. Moisture: PS 1-22 allows up to 18% at the time of shipment.
6. Faces and edges: knotholes, splits and edge voids within the grade.
7. Installation gap: tell the site to leave 1/8 inch between panels so they do not buckle as they take up moisture; APA publishes this as a builder tip, with design capacities in Forms D510 and Q225.

Photograph any sheet that fails with its stamp in the frame, and keep it apart from the rest.

How to order construction plywood

Order construction plywood by the stamp lines if you need a stamp, or by the full specification if you do not. Copy the line that fits:

PS 1-22 [Rated Sheathing], span rating [32/16], [15/32] Performance Category, [Exposure 1], [Structural I if required], agency mark and mill number on each sheet, [quantity], [port].

Exterior plywood, phenolic (WBP) bond, face/back C/D, core [Eucalyptus, stitched], [12] mm ± [0.5] mm, [1220 × 2440] mm, [quantity] sheets, [port].

For the second line, send it through our exterior plywood page. We reply within hours and send free samples.