What Is APA Rated Plywood? (How to Read the Grade Stamp)

APA Rated plywood is a panel that carries the APA trademark, which means the mill built it under APA’s quality-assurance program with third-party audits. The mark is not a grade: the span rating, exposure class, thickness and mill number printed beside it say what the panel can do, and an APA Rated panel is not always plywood. This guide reads a stamp field by field and sorts out PS 1, PS 2 and PRP-108.

What Does APA Rated Mean on Plywood?

APA is the trade association whose trademark appears on the panel. By its own description, the mark appears only on products made under its quality assurance, inspection and testing programs, and that program includes unannounced inspections at every participating mill (APA). So “APA Rated” tells you who built and audited the panel. It does not rank the panel. One APA-stamped sheet can be a sanded A-C face panel and the next a rough C-D sheathing panel.

APA says its trademark program inspects every participating mill without warning. Source: APA, How to Read an APA Trademark Stamp

“Rated” is also APA’s own wording. Its panel names are APA Rated Sheathing, APA Rated Sturd-I-Floor and APA Rated Siding, so the phrase “APA approved plywood” that people search for is not how the products are named. And none of those names says “plywood.” APA Rated Sheathing is defined as a wood-based structural-use panel, which is why OSB can carry the same kind of stamp and span rating.

What Does APA Stand For? American Plywood Association vs. The Engineered Wood Association

APA was founded in 1933 as the Douglas Fir Plywood Association, became the American Plywood Association in 1964, and has been APA, The Engineered Wood Association, since 1994. It is a nonprofit trade association with member mills in the United States and Canada, and it provides quality assurance, testing, certification and standards work (APA overview).

The name changed because members make more than plywood: OSB, glulam, wood I-joists and structural composite lumber too. Searches for the American Plywood Association, APA wood, and APA Engineered Wood Association all point to the same organization, and the same trademark.

How to Read an APA Grade Stamp, Field by Field

A full stamp has several fields, and which ones appear depends on the product. The sheathing example below is illustrative, not a real mill’s mark: APA RATED SHEATHING, 32/16, 15/32 INCH, SIZED FOR SPACING, EXPOSURE 1, mill number, PS 2.

Stamp field	What it tells you	Where it matters
Panel grade or end-use name	Veneer grades (A-B, B-C) or a name such as APA Rated Sheathing	Choosing sheathing vs a sanded face panel
Span rating (32/16)	Maximum support spacing in inches: roof on the left, subfloor on the right	Rafter and joist spacing
Sized for spacing	Panel is made slightly under 48 x 96 inches to leave a gap	Layout and expansion gaps
Exposure (Exterior or Exposure 1)	How much weather and moisture the glue bond is designed for	Indoor vs exposed jobs
Decimal thickness	Thickness in decimals, generally at or near the lower tolerance	Fitting hardware, dados, flooring heights
Mill number	Identifies the plant that made the panel	Tracing a panel to its source
Product standard (PS 1, PS 2, PRP-108)	The standard the panel was made to	Code and spec sheets
Performance Category (CAT)	Thickness designation tied to IBC and IRC nominal sizes	Reading “23/32” vs “3/4 inch”

Every row above comes from APA’s own stamp guide, except the span-rating details on specific panel types, which come from our own breakdown of the PS 1 standard.

Span Rating: The Two Numbers Separated By A Slash

A span rating like 32/16 gives two maximum center-to-center support spacings in inches. The left number applies to roof sheathing with the long dimension across the supports, and the right number applies to subflooring. A 32/16 panel suits rafters 32 inches apart or floor joists 16 inches apart. These are recommended spacings, and local building codes set the actual allowed spans, so check yours before sizing a roof deck. If you are weighing a thin panel overhead, our guide on using 1/2 plywood on a roof walks through that choice.

Not every stamped panel carries one. A sanded A-A cabinet panel has no span rating, and single-floor panels show a single floor-spacing number such as 16, 20 or 24 instead. For veneer grades and grade limits, see our DOC PS 1 plywood guide, which covers the PS 1-22 tables in full.

Exposure Durability Classification: Exterior vs. Exposure 1

APA says exposure classes for structural panels are Exterior or Exposure 1, based on the severity and duration of weather and moisture the panel is designed to take. Exterior panels handle repeated wetting and redrying or long-term weather exposure. Exposure 1 panels handle construction-stage moisture, but are not meant for long-term weather. That distinction is about the glue bond, so even an Exterior panel still needs a finish.

Older guides list four classes, including Exposure 2 and Interior. PS 1-07 eliminated the interior and intermediate bond types, so a current stamp reads Exterior or Exposure 1. If you find an old panel marked Interior, it was made before that change and is not a safe pick for any wet or exposed job.

What Does CAT Mean On A Plywood Stamp?

CAT stands for Performance Category, a panel designation tied to the thickness range and linked to the nominal thickness sizes used in the International Building Code and International Residential Code. It is not a competing rating to APA: it is one more field on the same stamp. PS 1-09 introduced Performance Category thickness labels, so “CAT PS 1” simply means the panel is labeled by category under that standard. The categories overlap, so a 3/4 inch label alone does not tell you the true thickness. Our 3/4 inch plywood price guide shows how that plays out at the lumberyard.

Decimal Thickness and Mill Number: The Two Fields People Skip

APA says the decimal thickness is generally at or near the lower tolerance in PS 1 or PS 2, so expect the real board to measure at that number or slightly above it, not above the nominal label. If you are fitting a dado, a hinge plate or a floor transition, measure the sheet or use the decimal number instead of trusting “3/4.”

The mill number is more useful than it looks. APA’s certified manufacturers directory lists each plant with its mill number: for example, Georgia-Pacific’s Madison, Georgia plant appears as mill 404, making plywood (APA directory entry). That lets you match the number on a stamp to a real plant, something the stamp’s logo alone does not let you do.

PS 1 vs PS 2 vs PRP-108: Which Standard Is on Your Stamp?

The product standard line can read PS 1, PS 2 or PRP-108. They are different documents, and mixing them up is why “APA spec” searches turn up so many half answers.

Standard	Who publishes it	What it covers
PS 1	U.S. Department of Commerce, administered by NIST; initiated by APA	Structural plywood only: veneer grades, species groups, glue bonds (current edition PS 1-22)
PS 2	U.S. Department of Commerce, administered by NIST	Performance standard for wood structural panels, plywood and OSB alike; finalized in 1992
PRP-108	APA	APA’s performance standard and qualification policy; the technical basis for PS 2

PRP-108 was developed by APA in the early 1980s for Rated Sturd-I-Floor and Rated Sheathing, and Rated Siding was added in 1984. PS 2 was built on its technical criteria. The 2021 edition of PRP-108 still covers all three products, but it refers to PS 2 for Sturd-I-Floor and Sheathing, and APA’s stamp guide describes PRP-108 as the document that sets qualification and marking for Rated Siding. In practice: expect PS 1 on veneer-graded plywood, PS 2 on span-rated sheathing and subfloor panels (plywood or OSB), and PRP-108 on siding.

What Does CDX Mean, And Is It The Same As APA Rated?

CDX is a trade nickname for a C-face, D-back panel, and APA states that panels commonly called CDX are Exposure 1, not Exterior. It describes a grade-and-exposure combination, not a separate rating system, and a CDX sheet can also carry the APA mark. “APA Rated” tells you who certified the panel, while “CDX” is shorthand for what that stamp says about its grade. See our ACX vs. CDX comparison for a project-by-project choice, or our CDX plywood vs. OSB comparison if you are deciding between sheathing types.

Which APA Rated Panel Fits Which Job?

APA product	Intended use	What the stamp shows
APA Rated Sheathing	Roofs, subfloors and walls, fastened to supports spaced per the span rating	Span rating such as 32/16, exposure class, thickness, mill number
APA Structural I Rated Sheathing	Where cross-panel strength and stiffness or racking shear matter most	Same fields, plus the Structural I designation
APA Rated Sturd-I-Floor	Combination subfloor and underlayment	A single floor-spacing number, plus tongue-and-groove if applicable
APA Rated Siding	Exterior siding	Exterior bond, span rating and nominal thickness
Veneer-graded sanded panels (A-B, A-C)	Cabinets, furniture, visible faces	Face and back grades, species group and exposure, usually without a span rating

Overlaid panels such as MDO are a separate product. They fall under PS 1’s Special Exterior grades, and our where to buy MDO plywood guide covers where to find them.

Common Misreadings of the APA Stamp

• “APA Rated means plywood.” Not necessarily. APA Rated Sheathing is a structural-use panel, and OSB is made to PS 2 and PRP-108 as well.
• “The APA logo is the grade.” The logo is a quality-assurance mark. Grade, span, exposure and thickness are separate fields printed beside it.
• “Exposure 1 is fine outdoors.” It is not. Exposure 1 covers construction-stage moisture, not long-term weather.
• “The span rating is the code limit.” It is a recommended maximum spacing, and local codes decide actual spans.
• “3/4 inch means 0.75 inch.” The Performance Category and decimal thickness fields tell you the real number.

How to Check a Panel Before You Buy

1. Find the stamp. It is printed on the face or edge of the panel, so check the sheet you are actually buying, not just the stack’s label.
2. Read the exposure class. Exposure 1 is for covered work, and Exterior is the minimum if the panel will see repeated wetting.
3. Match the span rating to your framing. Compare both numbers to your rafter or joist spacing, and confirm your local code.
4. Check the decimal thickness. Use it, not the nominal size, for any fit-sensitive work.
5. Look up the mill number. Match it against APA’s certified manufacturers directory if you want to confirm the panel’s source.

Store panels flat and dry, lift them rather than dragging, and cover them if they must sit outside. Our DOC PS 1 guide notes that PS 1 caps panel moisture content at 18% when a sheet ships, so a visibly wet sheet is a defect worth rejecting at the rack.

Frequently Asked Questions

What Is APA Rated Plywood?

APA Rated plywood carries the APA trademark, which means the panel was made under APA’s quality-assurance program with third-party inspection. The trademark is not a grade. The span rating, exposure class, thickness and mill number on the stamp say what the panel is for.

Is APA Rated Plywood Waterproof?

No. An Exposure 1 stamp covers construction-stage moisture, and an Exterior stamp covers repeated wetting and redrying, but neither makes the panel waterproof. The classification describes the glue bond, so cut edges and faces still need a finish when exposed.

Is CDX The Same As APA Rated?

No. CDX is a trade nickname for a C-face, D-back panel, and APA says panels commonly called CDX are Exposure 1. APA Rated tells you who certified the panel, while CDX describes a grade and exposure combination. A CDX sheet can carry the APA mark.

What Does The Span Rating On An APA Stamp Mean?

The span rating, such as 32/16, gives two maximum support spacings in inches. The left number is for roof sheathing and the right is for subflooring. A 32/16 panel suits rafters 32 inches apart or joists 16 inches apart, and local codes set the actual allowed spans.

What Does PRP-108 Mean On A Plywood Stamp?

PRP-108 is APA’s own Performance Standards and Qualification Policy for wood structural panels. It was the technical basis for PS 2, and its current edition covers Rated Siding while referring to PS 2 for Sturd-I-Floor and Sheathing panels.

How Can I Verify An APA Stamp?

Read the mill number on the stamp and match it to a plant in APA’s certified manufacturers directory, which lists each plant’s location, mill number and products. APA also says it runs unannounced inspections at every participating mill.

Is APA Rated Sheathing Always Plywood?

No. APA Rated Sheathing is defined as a wood-based structural-use panel, so it can be plywood or OSB. Both are made to PS 2 and can carry span ratings.

Conclusion

An APA stamp is a bundle of separate facts, not a single quality score. Read the exposure class first, match the span rating to your framing, measure the decimal thickness, and check the standard line. For grade limits and the full PS 1-22 tables, our DOC PS 1 guide goes deeper.