Wood Grades: What is Industrial Grade Southern Yellow Pine?

One of the questions that we frequently get from procurement managers is about wood grades.  As a pallet and crate manufacturer, and industrial wood seller, we primarily buy and sell industrial grade lumber.

But what kind of wood grades fall under the term “industrial grade”?

Southern yellow pine (SYP) obviously comes from southern yellow pine trees, and it is produced in several different wood grades and board sizes.  As with dimensional lumber sizes, different wood grades tend to be better suited to different types of projects.

Let’s talk about how SYP is graded.

Wood grades are determined at the mills, where southern yellow pine logs are cut into dimensional lumber.  Wood is usually visually inspected, according to the rules of the Southern Pine Inspection Bureau (SPIB), a non-profit organization.  The SPIB is responsible for maintaining the standards of lumber grading and manufacturing practices to ensure that the American Lumber Standard is consistently upheld across the lumber market.

SPIB member mills account for about 60% of the total production of SYP and approximately 95% of all the SYP that is classified and commercially sold in the United States.  Mills must have a grading license, requiring specific standards of producing, seasoning, and grading southern yellow pine, and prove that they are conforming to the basic provisions of the American Lumber Standard.

Members who meet all the requirements obtain a grade-marketing license and stamp their products.  Lumber is stamped to provide consumers with confidence that the lumber is up to standards.  Member mills are also periodically audited to ensure that they continue to meet SPIB standards.

The most common wood grades for SYP include #1, #2, #3, and #4, but there is also lumber that is rated as prime, dense or select structural, machine stress related, and several other categories related to structural lumber, flooring lumber, and furniture grade lumber.

For purposes of our discussion here, we’re going to stick with grades #1-#4. Each grade limits certain characteristics within the wood, such as knots, splits/checks, wane, and any type of twist, bow or crook in the wood.  We’ll talk more about this in a minute.

There are also different methods for determining wood grades.  While southern yellow pine is usually visually graded at the mill, there are actually three different methods for determining wood grades.

1. Visually Graded Lumber – This is the oldest and most common way of determining wood grades. Wood graders at the mill must be qualified, according to the SPIB standards, and then they must sort through every piece of lumber.  They are looking for specific visual characteristics that determine which grade each piece of lumber should be.
2. Machine Stress Rated Lumber (MSR) – As the name indicates, this type of grading is done with a machine, and usually only applies to wood for use in applications where strength is critical, such as joists, rafters, or trusses. Each piece of lumber is tested and shorted into stiffness and bending classes.  It must also meet particular visual requirements.  MSR lumber is not generally used in industrial lumber applications.
3. Machine Evaluated Lumber (MEL) – As with MSR, MEL is also mechanically tested using non-destructive grading equipment, and then checked for visual requirements, before being sorted into wood strength classifications.

The main difference between MSR and MEL grading is that MSR is primarily testing the elasticity of the wood and MEL is testing the density.

As we said earlier, we’re going to primarily discuss wood grades #1-#4, and each of these categories limits certain characteristics within the wood.  While there are a number of characteristics considered, like the size (and type) of knots, it gets complicated (and pretty boring) quickly.  Instead, here are a few basics that come into play when wood is graded.

Knots – A branch or limb embedded in a tree and then cut through during processing.  Knots are classified according to size, quality, and occurrence.

Splits/Checks – A lengthwise separation of wood, normally occurring across or through the rings.  It usually occurs as a result of seasoning.  Splits or checks are classified as small, medium, large, end check, or through check.  A check can also occur as a surface check.

Wane – The presence of bark or the lack of wood on the edge or corner of a piece of lumber.

Decay – When part of the wood has disintegrated due to wood-destroying fungi.

Mold – Black or greenish-brown patches on the surface of the wood, generally caused by humidity.  Discolored wood is often mistaken for mold.

Bow – On the wide face of a board, the ends curve up, rather than laying flat.

Twist – When all four faces of a piece of lumber spiral or twist.  This is usually the result of seasoning.

Crook – Similar to a bow, only it occurs on the narrow face of a piece of lumber.

As we already discussed, there are a lot of different grades of lumber.  Dense grade has superior density and strength and is used for structural purposes.  Prime and Clear grades are used when appearance matters.  There are even decking wood grades.

Frankly, it can get a bit complicated, but for the purposes of this conversation, we’re only going to focus on the industrial wood grades.  Generally, industrial lumber comes in grades #1 through #4 and are used for commercial and industrial applications.  There are some companies that draw further distinctions between the grades. – for example, #1 Grade and #1 Prime – but we’re just going to stick with the basics.

#1 Grade – This wood grade is considered a construction grade lumber suitable for siding, shelving, and paneling.  It contains a moderate number of tight knots that are unlikely to fall out, very little wane, and generally isn’t bowed, twisted, or crooked.  There is also #1 Grade wood that has been stress graded for use in framing, studs, rafters, etc.

#2 Grade – The uses for #2 Grade wood are similar to #1 Grade,  but has more (and bigger) knots, and may have more wane.  This is considered standard lumber and is often what you see in the big box stores.

#3 Grade – This wood grade is considered a utility/economy grade.  It may contain splits, knotholes, and a considerable amount of wane.  #3 wood can be used for sheathing, subflooring, concrete forms, among other utility-type applications.  This wood isn’t very pretty.

#4 Grade – #4 Grade wood is considered economy wood and it’s what we build most of our pallets and crates out of.  It’s also great for dunnage and banding groove.  It’s the least expensive wood option that still carries the strength to be effective for industrial applications.

For all intents and purposes, #4 Grade is the wood that’s left out of a log, after all the higher grades have been cut out of it.  It contains a lot of knotholes, knots, and wane, it may be twisted, bowed,  or crooked, and it may even have small bits of decay and a minimal amount of mold/wood discoloration.  This is not pretty wood.

The biggest reason we use #4 Grade lumber (and occasionally #3 Grade) to build our pallets and crates out of is the fact that it is the most cost effective, while still providing the strength our customers need.  For many manufacturers, the pallets and crates that they use to ship their products is never seen by consumers.  It doesn’t need to be pristine and pretty.  It needs to be tough, durable, and protect their products.

Why spend the extra money for pretty wood when #4 Grade will get the job done?