Hardwoods vs. Softwoods
The terms "hardwood" and "softwood" can be deceiving, as there are types of each which defy their names' implications. Hardwoods are derived from deciduous trees and include mahogany, oak, birch, and walnut. Softwoods come from evergreen conifer trees and include pine, cedar, fir, and spruce.
The National Hardwood Lumber Association established standards for grading lumber that are based on the number of defects in a board. The highest grade is FAS (or Firsts and Seconds), followed by lower designations that include, in order, Select, No. 1 Common, and No. 2 Common.
Softwoods are split into two categories and graded according to the American Softwood Lumber Standard. Dimensional, or "construction," lumber is graded on strength, while "appearance" and remanufacture lumber—boards that provide the raw material for other products—are graded on looks. The two primary grades are Finish followed by Select, each with letters A, B, C, and D as subgrades. The further down the alphabet, the more defects.
Boards differ in appearance and behavior depending on how they've been cut from a log. Plain-sawn cuts, also called flat-sawn, slice the log through the center. It is the most common method because it is fast and there isn't much waste. You can recognize this cut by the cathedral peak pattern of the grain.
In quarter sawing, the log is first quartered, and then each board is cut successively along the axis of the wedge, which yields fewer, but sturdier, boards. It has speckled, ribbon patterned grain.
Rift sawing cuts along the radius of the log so the grain pattern is the same in each cut. This technique results in the strongest boards, but they cost more.
Pressure-treated lumber contains chemicals that seal the wood to protect it from fungi, insects, and decay, so it's the best choice for outdoor projects. Because it is typically manufactured from pine, however, treated lumber can be susceptible to warping, swelling, and even water retention, so some routine maintenance is required.
Dimensional lumber is a term used for softwood that is cut to standardized sizes according to width and depth, such as 2x4s or 4x4s. This is one of the most popular woods for builders and DIYers because of its consistency. However, it is important to note that the size it is labeled as is not its actual dimensions.
What does this mean? All dimensional lumber has a nominal size and an actual size. The nominal size is what the wood is called, such as 2x4. Because the wood shrinks during the sawing and milling process the actual size of the lumber is 1 1/2 x 3 1/2. Typically, the actual size is 1/2-inch shorter than the nominal size. Rest assure, dimensional lumber is universal, so the 4x4 you buy at one store will be the same if you get another piece elsewhere.
Composite wood is a mixture of wood fiber and plastic that forms a material denser and stronger than wood. Though it costs a little more and is available in fewer colors than real wood, it's the lowest maintenance option for those not interested in sanding, staining, or splinters.
Plywood and Oriented Strand Board
Plywood and oriented strand board (OSB) are both structural panels that are used widely in framing and subfloors, but each has its own strengths and weaknesses. Plywood is lighter, off-gasses less, swells less, and retains less water than OSB. OSB, however, is generally more uniform and more affordable, and it's considered the "greener" of the two options. Learn more about the differences between plywood and OSB here.
Defects are most easily divided into five groups that encompass both manmade and naturally occurring imperfections: conversion, which refers to defects that are created during processing of the lumber, such as improper sawing or chips caused by a falling tool; fungus resulting from high humidity and warm air; insects such as carpenter ants or termites; natural forces like abnormal tree growth; and improper seasoning from the uneven drying of lumber.
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