Complete Guide to Lumber Grades
Oct 20, 2020
The idea of lumber should be simple: it is a log that has been sawn or cut to be used for building or woodworking projects. But the specifications of lumber are myriad—it’s sold in multiple sizes, cuts, and types. Furthermore, different types of wood have different characteristics, such as density, hardness, and compression strength, which make some types of lumber better for some projects than others.
If you know the basic characteristics of lumber, choosing the right pieces for the job can be much easier—and will help you avoid the potential pitfalls of using the wrong piece of wood for the job.
4 Characteristics of Lumber
Here are four important characteristics of lumber, all key as you choose which type of to use for certain projects:
- Density. One physical property of wood that builders must consider in their projects is density, or the actual wood material in a unit volume of wood. Expressed in units of mass divided by volume, the higher the number the denser the wood. Dense wood is best for furniture and building, and softer, less dense wood can be ideal for making engineered wood products and paper.
- Texture. Wood texture describes how a wood feels, from coarse to fine, given an equal amount of sanding. The size and distribution of the pores of wood contribute to its texture; for example, a wood species with large open pores like red oak will likely finish with an uneven texture. Depending on its texture, treating the wood will be less or more necessary to achieve a smooth finish.
- Color. Wood colors come in a veritable rainbow of hues, and while choosing a wood of a certain color may be made for hardness reasons (such as ebony), its distinctive color makes it an aesthetic choice, as well.
- Grain. Every tree has its own wood grain pattern, or the lines that naturally appear in lumber that indicate the direction in which the wood cell fibers grew. The grain direction is crucial to understand in construction projects. A straight-grained board is generally the strongest, and the grain pattern density is one determiner of strength.
How is lumber graded?
With so many variables among the physical properties of wood and the desirability of their characteristics, the construction industry relies on a set of grading standards for lumber—or a standardized way to judge the quality. They indicate how a builder can use each piece of wood for construction and what they can expect from the quality of the wood. Because of the major differences between hardwood and softwood, each type of wood has its own grading system.
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Softwood Lumber Grading
The US Department of Commerce sets the standard for softwood lumber in the United States, and it publishes guidelines in the form of the American Softwood Lumber Standard. Softwood is categorized into two categories of use: construction or remanufacture (such as wood that goes through a secondary manufacturing process to become paper, boxes, and so forth). For these purposes, we’ll discuss construction grading.
Softwood lumber used for general construction can be subdivided into three categories:
1. Non-stress graded
The structural integrity of the wood is the primary requirement. Lumber is graded primarily on its functionality but the appearance is still considered, especially in the higher grades. The more knots and defects in the boards, the lower they’re graded. The grades within this category are No. 1 (Construction), No. 2 (Standard), No. 3 (Utility), and No. 4 and 5 (both classified as Economy).
2. Stress graded
This type of lumber is also known as dimensional lumber, which you’ll recognize as a 2” x 4”. Dimensional lumber is used for posts, beams, decking, studs, rafters, joists, and for other structural uses where it will bear a weight (or stress). To make their use consistent, safe, and standardized, the United States uses a single set of grade names and descriptions. They’re graded based on strength, stiffness, and uniformity of size. The grades within this category are:
- Structural Light Framing: Lumber that’s between 2”x2” and 4”x4.” Commonly used for engineered wood trusses, it’s graded from No. 1–3.
- Light Framing: This uses the same size range as structural light framing, and is best for wall framing, windowsills, and other uses in which the lumber doesn’t need to bear as much weight. They are divided into construction, and utility quality.
- Stud: This refers to any lumber size and applies to lumber used vertically in a load-bearing wall.
- Structural joists and planks: The largest of the lumber grades, this classification is for softwood lumber between 2”x5” and 4”x18”. This grade is used for ceiling joists, rafters and floor joists. They’re graded from select structural to No. 1, 2, and 3. No. 3 is utility or economy grade.
As you might guess, the priority in this category is the appearance of the wood, and builders prize appearance-grade lumber for softwood furniture made with a natural finish or trim, siding and paneling.
However, not all appearance-graded lumber is designated the same way. For instance, different grade designations exist for some wood species and products that are markedly different colors. (Examples: Redwood boards are commonly graded Clear All Heart, Clear, and Select. Western white pine is graded as Supreme-IWP [industrial wood product], Choice-IWP, and Quality-IWP).
To simplify all these designations, most woodworkers and builders will recognize four letter grades for appearance lumber: A, B, C, and D. Grades A and B are combined into a single grade known as B and better (B&BTR).
Hardwood Lumber Grading
The designations for hardwood lumber grades are a bit easier to recognize, as all hardwood lumber uses a single set of grades. Appearance is one of the most important qualities in the grade, since most hardwood is exposed (such as in decking and flooring), and the highest graded lumber appears defect-free. Size matters in hardwood, since higher grades have a larger percentage of aesthetically pleasing usable material compared to lower grades.
Here is how hardwood lumber is graded:
- Firsts and Second Lumber Grades (FAS): These are boards wider than 6” and longer than 8’. To qualify in this highest category, boards must yield 83 1/3 percent clear face cuttings on both sides of the board. (This means that the portion of the board obtained by cross-cutting is clear on both sides.) The minimum size is 3” wide x 7’ long or 4” wide x 5’ long.
- FAS One Face (F1F): This meets the same standards as FAS, but only needs to meet the clear face requirement on one side.
- Selects (SEL): These meet the same requirements as F1F but can be smaller—a minimum of 4” wide and 6’ long.
- No. 1 Common: This designation refers to shop-grade or what’s commonly known as “cabinet-grade” wood. It’s smaller (3” wide x 4’ long) with a clear face of 66 2/3 percent.
- No. 2A and 2B Common: Used for paneling and flooring, it must yield 50 percent clear face cuttings and the boards must be 3” wide and a minimum length of 2’.
- No. 3A & 3B Common: This economy-grade wood only needs to yield clear face cuttings of 33 1/3 and 25 percent, respectively. Both must be 3” wide and 4’ long. They’re best for use in fencing and palettes.
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