Lumber Grading Guide For Decks

Your editor of Ideas-For-Deck-Designs.com Lumber grading is almost like a science in that there are fairly strict guidelines that the lumber companies follow so that consumers will be aware of what aesthetic and structural characteristics are to be found in the lumber they buy.

If you are building a deck or other structure that is highly visible, the lumber grading issue is a bit more important.

Grading lumber Grading lumber is based on a number of characteristics such as size, number and spacing of knots, any milling defects and any special curing techniques.

From these general criteria there are three grades, No. 1, No. 2 and No. 3. The lower the number the higher quality the grade of lumber.

But within each of these grades can be varieties such as No.1 Select Tight Knot, Standard Tight Knot or Clear.

Uses For Each Lumber Grade

No.1 grade lumber is usually from older growth trees so the grain is tighter and contains more heartwood so they look better, are more expensive and resist rot the best.

This kind of lumber is great for areas that are visible and exposed to the weather.

No.2 grade allows for more knots but is still good for weather resistance as it does not usually contain much if any sapwood. It's also less expensive so is probably your best value. And most building codes call for No.2 or better material.

No.3 grade allows for more knots but also tends to be less structurally sound so it is not a good choice for structural framing and its aesthetics makes it unsuitable for visible decking or railing. This grade of lumber is used sometimes for non-structural uses that don't have to look great.

Common Lumber Grading Defects

There are lots of terms used to specifically describe defects in lumber. Here are some of the most common:

Check

This is opening parallel with the grain, running lenghtwise with the board and looks a bit like an open fault line in the earth would. Checks occur when the surface of a board dries faster than the inside.

Crook

This is a bend in the board from end to end along the thin narrow edge.

Bow

This is a bend in the board from end to end along the wide flat face.

Split

This is a crack that occurs at the end of board and affects the strength of the lumber.

Cup

This is a bend across the width of board and comes to mind when you see deck boards that "cup" or hold rain water.

Twist

Imagine taking a board and turning each end in opposite directions like a screw. The result is a twist in the board.

Wane

This refers to an edge or shoulder along the length of a board that is missing or comprised of bark or sapwood.

This is not by any means an exhaustive list of how lumber grading is done but it should give you a good idea of what most of these terms mean the next time you are roaming the ailes of you lumber store.

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