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. 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 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 SOFTWOODS HARDWOODS Douglas  fir Basswood Southern  pine Willow Western larch American  elm Hemlock Mahogany* White  fir Sweet  gum Spruce White  ash* Ponderosa  pine Beech Western red cedar Birch Redwood Cherry Cypress Maple White  pine Oak* Sugar  pine Walnut* *Open-grained wood 3-26