Classification of Lumber

Trees are classified as either softwood or hardwood, as shown in Table 3. All lumber is therefore classified in the same way. The terms “softwood” and “hardwood” can be confusing since some softwood lumber is harder than some hardwood lumber. Generally, hardwoods are more dense and harder than softwoods. Lumber can be further classified by the name of the tree from which it comes. For example, Douglas fir lumber comes from a Douglas fir tree; walnut lumber comes from a walnut tree, and so forth.

The quality of softwood lumber is classified, according to its intended use, as being yard, structural, factory, or shop lumber. Yard lumber consists of those grades, sizes, and patterns generally intended for ordinary building purposes. Structural lumber is 2 or more inches in nominal thickness and width and is used where strength is required. Factory and shop lumber are used primarily for building cabinets and interior finish work.

Lumber manufacturing classifications consist of rough dressed (surfaced) and worked lumber. Rough lumber has not been dressed but has been sawed, edged, and trimmed. Dressed lumber is rough lumber that has been planed on one or more sides to attain smoothness and uniformity. Worked lumber, in addition to being dressed, has also been matched, shiplapped, or patterned. Matched lumber is tongue and groove, either sides or ends or both. Shiplapped lumber has been rabbeted on both edges to provide a close lapped joint. Patterned lumber is designed to a pattern or molded form.

Softwood Grading

The grade of a piece of lumber is based on its strength, stiffness, and appearance. A high grade of lumber has very few knots or other blemishes. A low grade of lumber may have knotholes and many loose knots. The lowest grades are apt to have splits, checks, honeycombs, and some warpage. The grade of lumber to be used on any construction job is usually stated in the specifications for a set of blueprints. Basic classifications of softwood grading include boards, dimension, and timbers. The grades within these classifications are shown in Table 4.

Lumber is graded for quality in accordance with American Lumber Standards set by the National Bureau of Standards for the U.S. Department of Commerce. The major quality grades, in descending order of quality, are select lumber and common lumber. Table 5 lists the subdivisions for each grade in descending order of quality.

Hardwood Grades

Grades of hardwood lumber are established by the National Hardwood Lumber Association. Firsts and Seconds (FAS) is the best grade. It specifies that pieces be no less than 6 inches wide by 8 feet long and yield at least 83 1/3 percent clear cuttings. The next lower grade is selects, which permits pieces 4 inches wide by 6 feet long. A still lower grade is No. 1 common. Lumber in this group is expected to yield 66 2/3 percent clear cuttings.

Lumber Sizes

Standard lumber sizes have been established in the United States for uniformity in planning structures and in ordering materials. Lumber is identified by nominal sizes. The nominal size of a piece of lumber is larger than the actual dressed dimensions.

Referring to Table 6, you can determine the common widths and thicknesses of lumber in their nominal and dressed dimensions.

You can see in Table 6 that nominal lumber sizes are a little larger than dressed lumber sizes. For softwood boards, there is a general rule to figure the dressed size of a piece of lumber, based on the nominal size. For boards with a nominal width up to and including one inch, the dressed size will be 1/4 inch smaller. For boards with a nominal width of two to six inches, the dressed size will be 1/2 inch smaller. For boards with a width larger than six inches, the dressed size will be 3/4 inch smaller. This rule may not be accurate in every case, so if there is any doubt about the size of a dressed piece of lumber, measure the piece.

Locally Procured Materials (Foreign Lumber)

You will have the opportunity to work on construction projects overseas. Be aware that the quantity and sizes of material, including lumber, will be different than what you work with in the United States. The Naval Facilities Engineering Command (NAVFAC offices take this into account when they solicit project plans from the local engineering firms. The local Resident Officer in Charge of Construction (RIOCC is well aware of the various products available in the project area and their intended use. The local Public Works Department or Supply Department is available for ensuring locally purchased material meets the specifications outlined for the project.