From exterior wall sheathing to cabinetry, plywood serves countless uses and is one of the most ubiquitous building materials, especially here in the Pacific Northwest. With so many uses and different types of plywood available, it’s important to know your options, understand the material, and pick the right product for your project.  

For our Plywood Series, we’re joined by T.R. Cauthorn, Panel Sales Manager at Hampton Lumber, a leading sustainable lumber producer based in Washington and Oregon and one of Dunn Lumber’s long-standing suppliers. With nearly 30 years spent with Hampton Lumber, plus experience working in mills and forests with Georgia Pacific, T.R. is a plywood expert.

In today’s episode, T.R. explains how to read a plywood grade stamp. He goes over the different information contained in APA – The Engineered Wood Association panel trademarks on plywood—an informational mark stamped on plywood to convey its intended use, the level of quality and identify the manufacturer in case there are any future warranty claims.

Watch our discussion in the video above and refer back to our guide below when needed. While the stamps used are from APA and adapted from its panel trademark examples here, T.R. notes that other organizations monitoring plywood quality and manufacturing standards also follow the same format. 

How To Read a Plywood Grade Stamp

1. Panel grade

Usually identified as the veneer grades used on the face and back of the panel (like “A-B”), or a name for the panel’s intended end use (like “APA Rated Siding”).

2. Span rating

On sheathing panels, the span rating is marked as two numbers separated by a slash:

  • The number on the left marks the maximum recommended center-to-center spacing (in inches) for supports when used for roof sheathing with the long dimensions across supports.
  • The number on the right marks the maximum recommended center-to-center spacing of supports (in inches) when used for subflooring with the long dimension across supports.
  • Span ratings on APA rated Sturd-I-Floor subfloor panels and APA rated siding are shown as a single number. The Sturd-I-Floor rating is based on the panel being used with the long dimension across at least three supports. The APA rated siding span number is based on the panel being used in a vertical position.

3. Tongue-and-groove

Panels that have a tongue-and-groove system of jointing have a marking of “T&G Net Width” followed by the measurement of the panel face. 

4. Bond classification

Exterior rated panels and Exposure 1 panels are produced with the same resin, however only exterior panels are designed for long-term exposure to the elements. This is due to Exterior rated panels allowing nothing lower than C grade veneer, where Exposure 1 panels allow for some D grade veneer.  Due to these compositional factors, Exposure 1 panels can delaminate or lose structural value when subjected to high levels of moisture or humidity over time.

Both Exterior and Exposure 1 panels should be stored properly on the job site.  This includes keeping them blocked up off the ground and wrapping them for protection from rain and snow.

No plywood panel is immune to swelling or movement once installed but following recommended nailing patterns and spacing requirements helps minimize this.

Lastly, Exterior grade panels in long-term exposure environments should be properly primed and painted as well as have a regularly scheduled maintenance cycle.

5. Decimal thickness declaration

Generally showing the lower tolerance (or near the lower tolerance) specified in PS 1 or PS 2. (PS stands for “product standard,” as further described below.)

6. Mill number

Identification number for the panel’s manufacturing mill.

7. Product standard

Abbreviated to PS followed by a number, this marks an industry-wide product manufacturing standard or performance specification.

  • Voluntary Product Standard: Developed by the plywood industry and U.S. Department of Commerce for structural plywood and shown as PS 1-19 
  • Voluntary Product Standard: Marks performance criteria for specific construction applications for wood structural panels and shown as PS 2-18

8. Performance category

A panel designation associated with the panel thickness range based on the nominal thickness designations used in the International Building Code (IBC) and the International Residential Code (IRC).

9. Siding face grade

Denotes the grade of the siding face, based on the maximum number of allowable repairs and appearance.

10. Species group number

Categorizes the panels’s strength under manufacturing standard PS 1, ranging from Group 1 to Group 5, with Group 1 being the strongest and Group 5 being the fifth strongest. 

11. HUD recognition

Recognition of wood-based Performance Rated Panels is contained in Use of Materials Bulletin UM-40.

12. Panel type, Canadian Standard

APA panels that are manufactured to meet both U.S. and Canadian standards (like the Rating Sheathing example above) show a dual mark. Otherwise, panels will only have a single mark representing either the U.S. or Canadian standard.

13. Span rating, Canadian Standard

The Canadian span marking uses “R” to represent roofs and “F” for subfloors.

14. Canadian performance-rated panel standard

Marked as “CSA-” followed by a number.

15. Panel face orientation indicator

Shows the direction of the panel’s strength axis. 

Have other questions about working with plywood? Browse through our Plywood Series archives for more guidance and information.