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.
Learn all about the properties of wood and how wood is used in construction in the MT Copeland course on Wood Materials. Taught by professional builder Jordan Smith, the course covers topics that range from I-joists to shear strength.
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: