Lumber Glossary
A comprehensive reference of lumber industry terminology. Whether you are a seasoned contractor or planning your first project with reclaimed wood, this glossary will help you speak the language of the trade with confidence.
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Lumber Industry Terms A to Z
Each term includes a clear, practical definition written for builders, designers, and homeowners working with reclaimed and new lumber.
Air-Dried
Lumber that has been dried by exposure to natural air circulation rather than a kiln. Air-drying is a slower process, typically taking several months to over a year depending on the species and thickness. The target moisture content for air-dried lumber is usually 12 to 20 percent, which is higher than kiln-dried wood.
Board
Lumber that is less than 2 inches thick and 2 or more inches wide. Boards are the standard form factor for shelving, paneling, trim, and furniture-making. They are distinguished from dimension lumber (2 to 5 inches thick) and timbers (5 inches or more in smallest dimension).
Board Foot
The standard unit of measurement for lumber volume. One board foot equals a piece of wood 12 inches long, 12 inches wide, and 1 inch thick, or 144 cubic inches. Board feet are calculated as: (Thickness x Width x Length) / 144, where all dimensions are in inches.
Check
A crack or split that runs along the grain of the wood, typically caused by uneven drying. Checks do not extend through the full thickness of the board. Surface checks are common in reclaimed lumber and generally do not affect structural integrity.
Clear Grade
The highest quality grade of lumber, virtually free of knots, splits, and other visible defects. Clear grade boards are prized for fine furniture, cabinetry, and architectural millwork where a flawless appearance is required.
Cross-Grain
Wood grain that runs at an angle to the long axis of the board rather than parallel to it. Cross-grain reduces the structural strength of the board and can cause unpredictable warping. It occurs naturally when a tree grows with a spiral or interlocking grain pattern.
Cupping
A form of warp where the edges of a board curve upward while the center drops, forming a concave shape across the width. Cupping is caused by uneven moisture content between the two faces of the board, often from improper storage or one side being sealed while the other is exposed.
Defect
Any irregularity in wood that reduces its strength, durability, or appearance relative to an ideal clear board. Natural defects include knots, checks, shakes, pitch pockets, and grain deviation. Manufacturing defects include chipped grain, torn grain, skips, and machine marks.
Dimensional Lumber
Lumber that has been milled to standard width and thickness dimensions, such as 2x4, 2x6, or 2x12. Dimensional lumber is the backbone of residential construction framing. Note that the actual dimensions are smaller than the nominal name: a 2x4 actually measures 1.5 by 3.5 inches.
Dressed Lumber
Lumber that has been planed or surfaced to a smooth finish on one or more sides after sawing. The designation S4S means surfaced on all four sides. Dressing removes saw marks and brings the board to a uniform thickness, but reduces its overall dimensions from the rough-sawn size.
End Grain
The grain pattern visible when wood is cut perpendicular to the length of the fibers, revealing the cross-section of the growth rings. End grain is highly porous and absorbs stain and finish differently than face or edge grain. It is also the strongest orientation for bearing compressive loads.
Face Grain
The grain pattern visible on the widest surface of a board when it is cut parallel to the growth rings. Face grain shows the most decorative figure of the wood and is the surface typically displayed in furniture, paneling, and flooring applications.
Figure
The distinctive pattern or visual character on the surface of wood created by grain structure, growth rings, color variation, and other natural features. Common figures include flame, birdseye, quilted, curly, and fiddleback. Figured wood commands premium prices in fine woodworking.
Flitch
A thick slab sawn from a log, or a bundle of veneers cut sequentially from the same log and kept in order. In the reclaimed lumber trade, flitch also refers to a rough-sawn slab with one or both edges retaining the natural bark line or wane of the tree.
Grain
The pattern and direction of wood fibers in a piece of lumber. Straight grain runs parallel to the length of the board. Other grain patterns include spiral, interlocked, wavy, and diagonal. Grain direction affects strength, workability, appearance, and how the wood absorbs stain and finish.
Green Lumber
Freshly sawn lumber that has not been dried, still containing its natural moisture content which can range from 30 to over 200 percent depending on the species. Green lumber is heavier, more prone to warping, and will shrink as it dries. It should not be used in finished applications until properly seasoned.
Growth Ring
The visible layer of wood produced during one growing season, seen as concentric circles on the end grain. In temperate climates each ring typically represents one year of growth. The number of rings per inch indicates the growth rate -- more rings per inch means slower growth and denser, stronger wood.
Hardwood
Wood from deciduous (broad-leaved) trees such as oak, maple, walnut, cherry, and ash. Despite the name, hardwood is a botanical classification, not a measure of actual hardness -- balsa is technically a hardwood. In practice, most commercial hardwoods are denser and harder than softwoods and are used for furniture, flooring, and cabinetry.
Heartwood
The dense inner core of a tree trunk, composed of older, non-living cells that have filled with resins, tannins, and other extractives. Heartwood is typically darker in color than sapwood and is naturally more resistant to decay and insect attack. Heart pine heartwood is among the most durable domestic woods.
Janka Hardness
A standardized test that measures the resistance of a wood species to denting and wear, expressed in pounds-force (lbf). The test measures the force required to embed a 0.444-inch steel ball halfway into the wood. Common ratings include Southern yellow pine at 870 lbf, red oak at 1,290 lbf, and hickory at 1,820 lbf.
Joinery
The craft of connecting wood members together using interlocking joints rather than mechanical fasteners. Traditional joinery includes mortise-and-tenon, dovetail, box joint, finger joint, bridle joint, and tongue-and-groove connections. Reclaimed lumber from older structures often features hand-cut joinery of exceptional quality.
Kerf
The width of the slot cut by a saw blade when cutting through wood. A standard circular saw blade has a kerf of about 1/8 inch. Kerf width matters when calculating material yield -- every cut wastes wood equal to the kerf width. Thin-kerf blades maximize yield from valuable reclaimed lumber.
Kiln-Dried
Lumber that has been dried in a controlled oven or kiln to reduce its moisture content, typically to 6 to 8 percent for interior use or 12 to 15 percent for exterior applications. Kiln-drying also kills insects and their larvae, which is especially important for reclaimed wood. The process takes days to weeks depending on the species and thickness.
Knot
A circular or oval section in lumber where a branch was connected to the trunk. Sound (tight) knots are firmly embedded and structurally intact. Loose knots may fall out, leaving a hole. Dead knots are black or dark-colored and surrounded by a ring of bark. Knots affect the grade, strength, and appearance of lumber.
Linear Foot
A measurement of length equal to 12 inches, without regard to width or thickness. Linear feet are commonly used for pricing trim, molding, and other narrow profile materials. It differs from board feet, which accounts for all three dimensions of the board.
Live Edge
A slab or plank that retains the natural edge profile of the tree, including the irregular contour where the bark was attached. Live edge pieces are popular for tables, countertops, shelves, and mantels where the organic silhouette of the tree adds visual interest and a connection to the natural form of the wood.
Moisture Content
The amount of water contained in wood, expressed as a percentage of the dry weight of the wood. A board with 20 percent moisture content contains water equal to 20 percent of what the board would weigh if completely dried. Moisture content directly affects wood stability, strength, and susceptibility to decay.
Nominal Size
The named dimension of a piece of lumber before it is dried and surfaced. A nominal 2x4 begins as a rough-sawn piece approximately 2 inches by 4 inches but finishes at 1.5 by 3.5 inches after drying and planing. Reclaimed lumber is often closer to its original nominal dimensions because older milling practices removed less material.
Old-Growth
Timber harvested from ancient, mature forests that developed over centuries without significant human disturbance. Old-growth lumber is characterized by extremely tight growth rings (20 or more per inch), high density, and superior structural properties. Virtually all old-growth lumber available today is reclaimed, as most virgin old-growth forests are now protected.
Pith
The soft, spongy center of a tree trunk, representing the very first growth of the sapling. Boards that include pith are prone to cracking and warping because the wood surrounding the pith dries unevenly. Sawyers typically avoid cutting boards through the pith when possible.
Plain-Sawn
The most common sawing method, where the log is cut with parallel passes through the full width. Plain-sawn lumber shows a cathedral or flame-shaped grain pattern on the face. It is the most economical cut but is more prone to cupping and warping than quarter-sawn or rift-sawn lumber.
Quarter-Sawn
Lumber sawn so that the growth rings are oriented at 60 to 90 degrees to the face of the board. Quarter-sawing produces straight, parallel grain lines on the face and reveals distinctive medullary ray patterns in species like white oak. Quarter-sawn boards are more dimensionally stable and less likely to cup than plain-sawn boards.
Reclaimed
Lumber or timber that has been salvaged from demolished buildings, bridges, barns, factories, and other structures for reuse. Reclaimed wood is valued for its environmental benefits, its aged character and patina, and the superior density of old-growth timber that is no longer commercially available.
Rift-Sawn
Lumber sawn so that the growth rings are oriented at 30 to 60 degrees to the face. Rift-sawing produces a consistent, straight grain pattern without the cathedral figure of plain-sawn or the ray fleck of quarter-sawn. It is the most wasteful cut and therefore the most expensive, but it produces the most uniform appearance.
S4S
An abbreviation meaning Surfaced Four Sides. S4S lumber has been planed smooth on all four long surfaces (both faces and both edges), resulting in uniform thickness and width. Other common designations include S2S (surfaced two sides, faces only) and S1S2E (surfaced one side and two edges).
Sapwood
The living outer layer of a tree trunk that conducts water and nutrients between the roots and crown. Sapwood is typically lighter in color than heartwood and is more susceptible to decay, insect attack, and staining because it lacks the protective extractives found in heartwood.
Seasoning
The process of reducing the moisture content of freshly sawn lumber to a level suitable for its intended use. Seasoning can be done naturally (air-drying) or artificially (kiln-drying). Proper seasoning is essential to prevent warping, cracking, and shrinkage after the lumber is installed.
Shiplap
A profile where each board is rabbeted on opposite edges so that adjacent boards overlap in a flush joint. Shiplap was originally used as exterior siding for weather-tightness. Today, reclaimed shiplap is extremely popular as an interior wall and ceiling treatment, prized for its clean horizontal lines and rustic character.
Softwood
Wood from coniferous (cone-bearing) trees such as pine, spruce, fir, cedar, and cypress. Softwoods generally grow faster than hardwoods and are the primary material for construction framing. Southern yellow pine, Douglas fir, and cypress are among the most important commercial softwoods in the Gulf South region.
Sound Knot
A knot that is solid, firmly embedded in the surrounding wood, and shows no signs of decay. Sound knots are acceptable in most lumber grades because they do not significantly reduce structural integrity. They are considered a desirable character feature in many rustic and farmhouse-style applications.
T&G (Tongue and Groove)
A milling profile where one edge of a board has a protruding tongue and the opposite edge has a matching groove. When installed, the tongue of one board fits into the groove of the next, creating a tight, interlocking joint. T&G is standard for hardwood flooring, paneling, and decking.
Timber
In commercial use, timber refers to lumber with a minimum dimension of 5 inches in its smallest cross-section. Heavy timbers are used for post-and-beam construction, bridge components, and other structural applications requiring large cross-sections. The term is also used generally to describe standing trees and forests.
Wane
The presence of bark or missing wood along the edge or corner of a board, where the round contour of the log was not fully squared during milling. Wane is considered a defect in standard grading but is sometimes valued in rustic applications. Significant wane reduces the usable width of a board.
Warp
A general term for any deviation from a flat, true plane in a piece of lumber. Warp includes bow (lengthwise curve on the face), crook (lengthwise curve on the edge), cup (crosswise curve on the face), and twist (spiraling distortion). Warp is caused by uneven drying, reaction wood, or grain irregularities.
Weathering
The natural degradation of wood surfaces caused by exposure to sunlight, rain, wind, and temperature changes. Weathering turns wood gray or silver, erodes softer earlywood grain, and can create a rough texture. In reclaimed lumber, controlled weathering produces a highly sought-after patina.
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