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.
Here are four important characteristics of lumber, all key as you choose which type of to use for certain projects:
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.
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:
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).
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:
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).
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:
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