Lumber 101

Have you ever gone into a home improvement store or a lumber yard and just stood there staring at all the lumber not knowing what you should get? Well, here are a few pointers to make your life a bit easier and your construction project turn out the way you intended.

Hardwood vs. Softwood

There are simple ways to know if lumber comes from a hardwood tree or a softwood tree. Hardwoods reproduce with seeds that have a hard cover -- like an acorn, hickory nut, or apple seeds. They are more dense, sturdier, and hard to cut.

Softwoods let seeds fall without coverings and are light enough for the wind to pick them up and spread them to great distances. Their foliage stays green during the winter, so it's safe to say that all evergreens and pines are softwoods. They are less dense and easier to cut than hardwoods.

Structural Lumber

Structural lumber is any lumber that is at least 2” thick and 4” wide. These are nominal dimensions, meaning that the actual dimension is most likely ¼ to ½ inch less. The most important thing about structural lumber is that it's meant to be used in load bearing or stressed areas. This includes beams, stringers, joists, posts, etc. Structural lumber is basically any lumber used to build a house.

Lumber, like what is referred to as a 2x4, is actually 1 1/2 x 3 ½ inches in size. This is called a “nominal” size versus the actual size. The 2x4 dimension comes from the size the board was when it was cut from the log. The actual size is the size after all the moisture has been removed. There are charts available if you don’t have a calculator for a brain. Or you can do what I do when I shop for lumber and bring a tape measure along.

Moisture Content

While a tree is growing, about 50% of that tree is water in one form or another. To use the wood to build a structure, the moisture needs to be reduced to about 12% in softwoods and 6% in hardwoods. One way to dry wood is in a kiln. Wood must be dried evenly. Cracks, cupping, and splitting occur if the wood is not dried evenly.

Even after wood is cut, it will absorb or release moisture according to its surroundings. During the summer, your house may swell because the wood absorbs moisture. In the winter, the house will shrink back. You may notice the floor squeaks during certain times of the year and not at others times. That is just one result of swelling and shrinking. Wood can shrink or swell as much as a ¼ of an inch in a home that has no humidity control. (This is just one reason why you will want any wood flooring you are planning on installing to acclimate to its surroundings by opening every box and letting it sit in the room where it is going to be installed for at least 24 hours.)

Dried timber is light and easy to transport. It's also stronger when dried, and less likely to attract insects. Insects need wood with moisture in it to survive.

Common Defects

There are many things that can go wrong with a piece of lumber. Most are a result of moisture content and what part of the log the board was cut from. The most common defects are cupping, bowing, knots, checks, and splits.

Cupping in a board makes it look concave on the face. Bowing looks as if you could use the board to make a rocking chair. Knots are dark, circular discolorations that are natural to wood and are remnants of branch growth. Knots are not always considered a defect -- some add to the attraction of a nice piece of wood.

A check is a crack on the edge of the lumber that goes all the way through (it looks like a crack). A split is similar to a check, but doesn’t go all the way through.

Translating Lumber Stamps

Every piece of lumber that comes out of a mill must have an inspection stamp. The stamp will identify the species of wood, the grade, the moisture content, a certification mark, and the mill of origin.

There are a few things you need to know before we try to explain how to read the stamp.

1. Clear wood is measured in percentages. The higher the percentage, the less knots or deformities the lumber has.
2. The “grades” you see on the stamp are a measurement of the percentage of clear wood.

For example: #2 structural means that at least 66% of the wood is clear wood. Select wood is 80% clear wood, #1 is 75% clear, #3 is 50% clear, construction grade is 57% clear, standard grade is 43% clear and utility grade is 29% clear wood. Most homes are made with #2 structural grade. As the numbers get higher, the quality goes down…and so does the price.

Moisture content (MC) is also within the stamp. S-GRN (surface green) has a moisture content greater than 19%. S-DRY (surface dry) has a moisture content less than 19%. MC15 has a moisture content less than 15%.

The following agencies (certified by) are the ones who develop the grade rules:

• Redwood Inspection Service (R1S)
• Northeastern Lumber Manufacturers Association (NELMA)
• Northern Hardwood and Pine Manufacturers Association (NHPMA)
• Southern Pine Inspection Bureau (SPIB)
• West Coast Lumber Inspection Bureau (WCLB)
• Western Wood Products Association (WWPA)

The species stamped on the lumber include:

1. S-P-F spruce, pine, or fir (softwoods)
2. DF-L Douglas fir and western larch
3. Hem-Fir western hemlock and true firs

Other stamps you may see are FSC which stands for Forest Stewardship Council. You will only see this stamp on wood that was harvested from a sustainable forest. D-blaze stamped on lumber means it was treated with a flame resistant chemical.

The mill of origin can be the mill's own name or trademark, or it can be a number that is assigned by a grading agency.

Plywood and Paneling

Both plywood and paneling are manufactured products. Plywood is thin sheets of wood (veneer) that are glued and pressed together at 90 degree angles. This improves the strength of plywood and makes it less likely to warp.

Paneling is typically a thin laminated board, similar to plywood with a finish to either one or both sides of the board. Paneling was originally used to insulate stone walled rooms. Now it is an inexpensive way to decorate a room. Paneling can also be made of plastic, but is most often made of wood byproducts.

Now you are prepared to talk turkey with the lumber guy.