Plywood Grade Stamp - Building Lumber

The picture below provides you with an excellent example of a plywood grade stamp that's used by house framers. It's not uncommon to find at least one or two of these stamps placed on a 4 x 8 sheet of plywood. The plywood grade stamp tells contractors, home builder's, engineers, architects and building inspectors, whether or not this plywood can be used for a specific part of the building.

Let's take a look at the plywood stamp and see what it tells us about the plywood. The APA stands for American Plywood Association. This tells the buyer that this piece of plywood was made at a lumber mill who is a member of the APA. I don't know if that really makes a big difference in the quality of plywood, but it does make some people feel better.

You can barely see the words, "Rated Sheathing," which isn't hard to figure out. Again wouldn't every plywood that had a grade stamp on it be rated. I seriously can't believe how many things they put on building products that don't need to be there.

A good example of this, is the fact that you can read APA and The Engineered Wood Association, on this particular piece of plywood, but it's hard to make out the next part. Since I've looked at enough plywood grade stamps, I can fill in the missing blanks, for you.

Underneath rated sheathing are the numbers 40 20. You're going to get a kick out of what these numbers really mean, but it doesn't make any sense. The larger number which is 40 represents an acceptable span for roof rafters and the smaller number represents the acceptable span for floor joist.

In other words, you can supposedly, use this piece of plywood for a roof with 40 inch on center roof rafters. Like I said, it doesn't make any sense, because I haven't ever seen roof rafters with spans more than 24 inches on center, using 3/4" plywood.

The 19/32 tells us how thick this piece of plywood is. This piece of plywood is usually referred to as 5/8 of an inch plywood. It's not uncommon to find a piece of plywood that's 1/16 of an inch thinner than the measurement referred to by most construction workers.

Exposure 1 means that the plywood can be exposed to moisture, but it can't be exposed for a long period of time.

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