Lumber comes in all shapes, sizes and qualities. The lumber grading system helps differentiate between the different woods and will help guide you in your selection of wood for your home construction project. Speak to your carpenter about which wood is best for your project.
Softwood lumber in the United States is most commonly graded according to the guidelines of the American Softwood Lumber Standard PS 20-70, established by the US Department of Commerce (source: woodbin.com). Below you will learn about the grading system for softwoods, the most common type of wood used for construction.
Hardwoods are graded differently. Most of the hardwood lumber in the United States and Canada is graded according to the rules established by the National Hardwood Lumber Association (NHLA). For more information on hardwood lumber grading, including a helpful chart, visit woodbin.com.
A General Guide to Basic Wood Grades:
The two main classifications of lumber are select lumber and common lumber. Select lumber is considered the finest and best for use in finishing projects, and common lumber is best for general building and construction.
Select Lumber Classifications:
Natural finishes are graded either A or B.
Grade A is nearly free of defects and blemishes.
Grade B contains a few minor blemishes.
Painted finishes are graded either C or D.
Grade C contains more significant blemishes, and more of them, than woods in Grade B.
Grade D has even more blemishes than Grade C does. Either grade, C or D, presents a satisfactory appearance when painted.
(Source: http://www.tpub.com/engbas/6-2.htm)
Common Lumber Classifications:
No. 1 (construction use) is sound, tight-knotted stock, containing only a few minor defects. No. 1 has no knotholes or other serious defects. It must be suitable for use as grain-tight lumber. Used for siding, cornices, shelving, paneling, some furniture.
No. 2 (standard use) grade has more and larger knots and blemishes than No. 1.
No. 3 (utility use) contains a few defects, larger and coarser than those in No. 2; for example, occasional knotholes. Does not take paint well. Used for crates, sheathing, subflooring, small furniture parts.
No. 4 is low-quality material, contains serious defects like knotholes, checks, shakes and decay.
No. 5 commonly holds together only under ordinary handling and where appearance is not important. This kind of wood is not paintable.
The first three grades are most commonly available in retail lumber yards.
