CLASSIFICATION OF LUMBER
Trees are classified as either softwood or
hardwood (table 3-3).
Therefore, all lumber is
referred to as either softwood or hardwood. The
terms softwood and hardwood can be confusing
since some softwood lumber is harder than some
hardwood lumber. Generally, however, hardwoods
are more dense and harder than softwoods. In
addition, lumber can be further classified by the name
of the tree from which it comes.
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.
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 3-4.
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
Table 3-3.-Different Types of Softwoods and Hardwoods
Western red cedar