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Lumber Glossary

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AC Exterior – A sanded plywood panel with an A-grade face, a C-grade back and C-grade inner plies. This is bonded with exterior glue.

Adaptive Management - Driving forest management with scientific research. This requires excellent monitoring, and feed back loops to quickly put new knowledge into practice on the ground.

Agroforestry - The combined production of both crops and trees to maximize water efficiency.

Air Dried – Seasoned without artificial heat. This method uses the atmosphere / air to naturally dry lumber.

…And Better – This is usually abbreviated with “&Btr” and is a grade of lumber signifying that an unspecified percentage is a higher grade than the lowest acceptable grade. For example, Std&Btr grades will contain some pieces of Standard Grade and some pieces of higher grades, such as Construction.

Arsenic Pentavalent Arsenate - The kind used in wood preservatives, not to be confused with commercially produced Trivalent Arsenic, which is not used in any wood preservative.  Pentavalent Arsenate occurs naturally in the soil, water, air, plants, and in most living creatures - including humans.

Artificial Regeneration - Establishing a new forest by planting seedlings or by direct seeding (as opposed to natural regeneration).

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Beaded – A decorated piece of lumber with a raised half-circle bead along the length.

Best Management Practices (BMP) - A forestry practice or combination of practices, determined by a state to be the most effective means of preventing or reducing the amount of nonpoint source pollution in order to protect streams and water quality. Some BMP's are defined by the state's Forest Practices Acts and their accompanying rules and regulations.

Bethel’s Process - Developed in 1938, the application of an initial vacuum followed by the impregnation of creosote formed a basis for the present wood-treating industry.

Board Foot – This is the standard unit of measure for lumber. One Board foot is equal to a 1 inch thick board 12 inches in width and 1 foot in length.


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Cambium - A single layer of cells between the woody part of the tree and the bark.  Division of these cells results in diameter growth of the tree through formation of wood cells (xylem) and inner bark (phloem).

Canopy - The forest cover of leaves, branches, and foliage formed by tree crowns.  There may be several canopy layers.

Casing – The trim around the top and sides of windows and doors.

CD-Exterior (CDX) – This is the standard grade of plywood sheathing used for various applications, including roofing. The “C” represents the grade of the front and the “D” represents the grade of the back. The “X” represents exterior glue has been used to adhere the plywood layers. However, this exterior glue will only withstand incidental exposure to weather.

Ceiling – A piece of patterned lumber that is tongue and grooved to be used on ceilings, predominantly in older homes. (Beaded Ceiling)

Cellulose - This is the primary material of wood cell walls and it is 100% non-soluble glucose.   Cellulose is a polymer chain carbohydrate (i.e. chains of sugar molecules, or polysaccharide) and is the main constituent of the cell walls of all plants, accounting for about 50% of the dry weight of wood.  Also, the basic raw material (chemical compound) used in papermaking. It is the most widely distributed organic (carbon-based) compound. It is not water soluble and is extracted by pulping.

Certification - Third party certification might reassure the end consumer of wood products that the wood was produced and processed in a 'sustainable' manner, without damaging forest ecosystems.   Certification tells the consumer that the wood is coming from a well managed or 'sustainable' forest operation where good stewardship is practiced.

CIS - Consumer Information Sheet, guidelines for handling treated wood, available to the consumer at retail outlets where treated lumber is sold.

Chromated Copper Arsenate (CCA) - A water-borne solution most commonly used on lumber, plywood, and timbers.  This preservative protects against insects (primarily termites), fungi, and marine borers. CCA is the most widely used of all pressure-treating wood preservatives.

Clear – A grade of lumber that signifies being practically free of all blemishes or defects. This is a very select grade of lumber.

Clear Cutting - In a clear cut, all the trees in a block are harvested so that a new crop of sun-loving (i.e. shade intolerant) trees can get off to a fast start. Clear cutting also facilitates mechanical planting. In some stands of trees a clear cut follows one or two "selective cuts" which thin out the trees that compete for sunlight, water, and nutrients. Today, clear cuts are smaller in size and are designed to blend in with the landscape. Many animals, such as deer, depend on clear cuts - which provide excellent forage. Clear cuts are prohibited next to streams and lakes which require buffer zones with selective harvesting, if any.

Clear Heart – This is the highest grade of Redwood. This grade is usually used in finish work were the finest appearance is desired.

Climax Forest - A forest community that represents the final stage of natural forest

Coniferous - Cone-bearing trees having needles or scale-like leaves, usually evergreen, and producing wood known commercially as 'softwoods.'

Conservation - The sustainable use of forest resources in a manner that does not degrade the collective resource values of a region over the long term.

Construction Heart – This is Redwood that consists of all heart with no sapwood. This grade has a high resistance to insects and decay so it is often used in applications where it will be exposed to the elements.

Crook – Any deviation in the edge based on a straight line from end to end of a piece of lumber. (Considered a warp)

Crown – This is the upper part of a tree. This also is the term for a slight camber on a horizontal member. The crown is generally placed to the top.

Cup – A flatwise deviation from a straight line across the width of a piece of lumber, measured at the point of greatest distance from the line.

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Dado – This is a groove cut into one piece of lumber to accommodate another piece of lumber. This is usually cut across the grain rather than a “rabbet” which is cut with the grain. This also is the term used for the lower part of an interior wall.

DBH - The diameter of a tree as measured at breast height. Standard dbh is measured at 4.5 feet above the ground.

Decay - Decomposition of wood by wood-destroying fungi.

Deciduous - Term applied to trees, commonly broadleaf, that usually shed their leaves annually. It is an adaptation to prevent excessive water loss by transpiration when water is scarce. Also known commercially as “hardwoods.”

Delamination – This is the separation of the layers of plywood at the glueline. This is usually caused by moisture or defective glue.

Double-End Trimmed (DET) – When a piece of lumber has been passed through saws so it is smoothly trimmed at both ends. Typically this is done in two feet increments – 8’, 10’, 12’, etc.

Dry - When is seasoned to a moisture content of less than 19% either by kiln or air.

Dry Kiln – Wood that is to be dried by applying heat and therefore withdrawing moisture is put in this chamber.

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Edge Grain – Vertical grain; a cut so the wide surfaces are at right angles to the growth rings. Also, the grain produced on quarter-sawn wood. Also, veneer cut within 45 degrees of the radius of the log and across growth rings.

End Matched – Lumber that has a tongue at one end and a groove at the other. This provides a tight end to end fit between pieces.

Endurers - Plants that re-sprout following a fire or endure the effects of fire.

Extractives - Chemical "wastes" which are stored in the heartwood of trees providing natural durability.

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Fancy Butt – This is a particular type of shingle with a machined butt end. These are used mostly used on sidewalls of buildings to form patterned designs.

Fasteners - The hardware (e.g. nails, screws, bolts, joist hangers) used to secure treated wood. Since treated lumber is used for durability, fasteners should be hot-dipped galvanized or stainless steel, especially with water borne preservatives, which contain corrosive salt.

Fiber - in papermaking this refers to the cellulose fiber. Softwood trees produce long cellulose fibers that are good for strength and hardwood trees produce short fibers that are good for smoothness. Fibers are often blended to create the ideal characteristics for a given paper.

Fingerjoint – This is a process of joining two pieces of lumber end-to-end by sawing the ends so they can be interlocked. When the pieces are glued and pushed together they form a strong joint.

Fire Retardant – A chemical applied to lumber or other product to deter the combustion of fire and flame spread. Also, a chemical used to fight forest fires.

Fixation - The chemical process in which the preservative metals in water-borne solution react with and bond to wood fiber molecules.

Forest - An ecosystem dominated by trees, with a unique combination of plants, animals, microbes, soil, and climate.

Foresters - Foresters manage forests for the maintenance and reoccurrence of desirable conditions. What is desirable is determined by social, biological, and economic considerations.

Forestry - The art, science, and practice of managing forest landscapes to provide a sustained production of a variety of goods and services for society.

Flat Grain (FG) – Rings formed annually that are at less than 45 degrees with the surface of the piece of lumber.

Flooring – This is a tongue and grooved piece of lumber usually in 1”x4” dimensions. It is sold as either flat grain or vertical grain and usually in Superior and Prime grades.

Forwarder - A machine with a crane which can load logs onto its chassis and piggy-back them to a road where it can sort and pile them or load them directly onto a truck.

Free oh Heart Center (FOHC) – Lumber that when sawn excludes the heart center or pith of a log. This will help prevent checking and cracking.

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Grade Marked – Most lumber is marked with a grade by the mill. It is graded for quality and / or use and stamped accordingly with a grading association or agency stamp.

Green – This is lumber that is unseasoned and not dry. Lumber with a 19% or more moisture content.

Groove – A narrow channel on a piece of lumber or plywood usually on the edge or face.

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Hardwood - A deciduous or broadleaf tree; also applies to the wood from such trees.

Heartwood – This is the inner / dormant part of the tree contained within the sapwood. Only the outer part is the living part and needed to survive.

Heavies – Shakes, usually cedar, that are 3/4'” to 5/4” thick at the butt end.

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Incising - Perforating the wood surface with small slits to improve the penetration and effectiveness of the preservatives. Not necessary with treated Southern Yellow Pine, Ponderosa Pine, and Red Pine.

Indigenous - Pertaining to plants or animals that are native to a particular region or country.

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KDAT - Wood that is Kiln-Dried after Treatment. Pressure-treating with water-borne preservatives adds moisture to the wood, which can be removed by kiln-drying.

Kiln Dried – Lumber, seasoned / dried in a kiln to a certain moisture point.

Knot - A spot on a piece of lumber, after being sawn, where a branch or limb had once grown. They are classified by quality, occurrence and size – the smaller is generally considered better in the grading process. (e.g. Pin Knot – 1/2” or smaller, Small – 1/2”-3/4”, Medium- 3/4"-1 1/2'”, Large – over 1 1/2") See knot occurrence and knot quality.

Kraft - a very strong type of wrapping paper made from a special type of chemically treated wood pulp. The Kraft (Sulfate) pulping process produces the best quality softwood pulp. Generally brown natural kraft but can be bleached white. Kraft is the German word for strength.

Knot Occurrence – Knots are classified by size, quality and also by occurrence on a piece of lumber. (E.g. Branch Knots, Corner Knots, Cluster Knots, Single Knot, Spike Knot) See knot and knot quality.

Knot Quality – Knots are classified by the quality of the knot along with the size and occurrence. Quality grades are determined by soundness, advanced decay, pith holes and other variables. See knot and knot occurrence.

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Laminated Veneer Lumber (LVL) – Veneers laminated together to form a large structural piece of lumber. Similar to a very thick piece of Oriented Strand Board (OSB) used for long spans where upright support beams are not feasible or desired.

Lath – Used as backing for wall plaster or other material, this is a thin, very narrow wooden strip.

Lattice – A small moulding (S4S) used predominately in trellis work.

Lignin - A polymer that binds cellulose together to make wood. The stiffening material inside wood cell walls that gives them strength and rigidity. Allows trees to grow tall and out-compete other plants for sunlight. This accounts for about 30% of the dry weight of wood.  Lignin is removed in the pulping and bleaching processes to brighten the paper and prevent yellowing.

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Moisture Content - The weight of water in wood, expressed as a percent of the oven-dried weight of the wood.

Multiple-Use Management - The practice of managing forest resources for a variety of simultaneous uses and benefits including water, forage, wildlife habitat, wood, recreation, wilderness, and minerals.

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NEPA - National Environmental Policy Act (1969) requires Environmental Assessments (EA) and Environmental Impact Statements (EIS). This act is the basic national charter for protection of the environment in the U.S.

Nominal Size – This is the size designation for most lumber and wood products. It is usually greater than the actual size. For example a 1”x6” piece of lumber usually measures 3/4”x5 1/2" after it is surfaced.

Nonrenewable resource - a resource that is in limited supply and doesn't have the capacity to be replaced through natural processes, at least not for many thousands of years.   Fossil Fuels are a nonrenewable resource.

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Old Growth - To most people "old growth" means big trees. The U.S. Forest Service definition is "a forest with trees 200 years or older, snags (standing dead trees), and down woody debris on the forest floor."

Overlaid Plywood – Plywood that has a surfacing material added to it (either on one side or both). Usually, this is to create a protective or decorative surface for finishing. These may include resin film, impregnated paper, plastics, or metal.


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Paint Grade – A grade of a wood product that signifies it is more suitable for painting rather than a clear finish. Paint Grade Spruce (PGS).

Penta (Pentachlorophenol) – This restricted chemical is usually applied under pressure to help in preserving wood. Oak Railroad Ties are often Penta treated.

Phloem - A layer of plant tissue just inside the bark that transports food (dissolved nutrients) from the leaves to the stem and roots.

Photosynthesis - Complex process that takes place in cells of green plants.   Radiant energy from the sun is used to combine carbon dioxide (CO2) and water (H2O) to produce oxygen (O) and carbohydrates (such as glucose) and other nutrient molecules.

Pin Knot – A knot with a diameter no larger than 1/2”.

Pitch – The accumulation of resin in wood cells in an irregular patch graded as light, medium, heavy or massed. This is also the term for the angle of a roof on a house.

Plywood – A flat panel made up of a number of layers. The layers are thin sheets, or veneers, of wood. The grain of the wood for each layer is at a right angle to the adjacent layer of wood creating added strength. The layers are bonded together.

Preservative - Any substance applied to wood that is effective in preventing the development and action of wood destroying fungi and insects.
ACA: Ammoniacal Copper Arsenates
ACC: Ammoniacal Copper Citrates
ACQ: Ammoniacal Copper Quaternary
ACZA: Ammoniacal Copper Zinc Arsenates
CCA: Chromated Copper Arsenates
PCP: Pentachlorophenol (Penta)

Pressure Treating - The process by which preservatives and/or fire retardants are applied to wood products. The treatment involves forcing the chemical, and sometimes water sealant, deep into the cellular structure of the wood under high pressure in a closed cylinder.

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Quarter Saw - To saw a log into quarters lengthwise and then into boards in order to show the wood grain to advantage. This shows the annual rings at angles of 45-90 degrees with the surface of the piece.

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Rabbet – This is a rectangular cut where two surfaces are cut on the edge of a member, parallel with the grain.

Random Lengths (RL) – Lumber of various lengths that are usually in two feet increments. A random length loading is presumed to have a fair representation of the mills production.

Random Widths (RW) – Lumber of various widths.

Redwood – Sequoia sempervirens is found in limited areas of Northern California and Southern Oregon and is naturally resistant to decay. It is used in many of the same applications as Cedar, especially siding and paneling. Sequoia gigantea is another species that grows in the Sierra Mountains of Central California and is protected from harvest.

Regeneration - The renewal of vegetation by natural or artificial means.

Refractory Species - Wood species that are difficult to treat. These species must be incised prior to treatment to meet AWPA standards.

Renewable Resource – This is a resource that has the capacity to be replaced through natural processes.  Trees are a renewable resource.

Reverse Board and Batten – This is a siding pattern where wider boards are nailed over the battens, giving a narrow inset. Rip – To cut a board along its length versus a cross cut along the width.

Rough – Term used for lumber that is not dressed or surfaced. The surface is the same as when it was first sawn from the mill. Surfaced lumber is referred to as smooth.

Rougher Headed – Lumber that has been run through a planer with notched knives. It has a rough sawn texture, but it is accurately sized.

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S1S2E – Term meaning surfaced one side and two edges.

S4S – Surfaced four sides.

Salvage - The harvesting of dead and dying timber while it still has commercial value is called 'salvage.' Trees impacted by fire, insects, and disease can often be salvaged.

Sapwood - The younger wood nearer to the surface of the tree, which does not have the natural extractives (chemicals) to prevent decay. (The outer layers between the bark and the hardwood that contains the sap)

Saw Textured – A texture intentionally put on a piece f siding or paneling to give it a textured or rough appearance.

Sealant – Water repellents which may be forced into the wood along with the chemical preservative in a closed cylinder under pressure. However, treated wood should be cleaned and resealed yearly to maintain optimum appearance.

Seasoning - Wood is both air-dried and steam kiln-dried to reduce the water content.

Select Structural – The highest grade given to Planks and Structural Joists. This grade is given to lumber with high quality in appearance, strength and stiffness.

Select Tight Knot (STK) – A grade often used referring to cedar lumber. STK lumber is graded based on the tightness or strength of the knots differentiated from lumber containing loose knots or knotholes.

Serotinous - A pine cone or other seed case that requires heat from a fire to open and release the seed.

Shade-tolerant - The capacity of a tree or plant species to develop and grow in the shade of, and in competition with, other trees or plants.

Shake – A separation lengthwise between growth rings. Examples are: fine, slight, medium, open, cup, round, ring, shell, through, and pith. Shake is also a name for roofing material usually made from cedar. They usually have one surface with a natural grain texture / spilt surface.

Sheathing – Plywood, waferboard, oriented strand board or lumber used for roofs, floors, or to close up walls prior to the finish materials being applied.

Shim – A small piece of material used as a wedge in construction. Or, a narrow piece of wood, not more than 3/16” wide, used in replacing defects in plywood.

Shiplap – Lumber that has been cut to form a rabbeted edge on each side so when put next to each other the pieces may be fitted snugly together for increased strength and stability.

Silviculture - The art and science of growing and tending a forest (managing stands of trees to achieve desired outcomes relative to species composition and stand structure).

Softwood - A coniferous tree.  The term softwood is commonly used but not strictly accurate; the wood of many conifers is harder than that of some so-called hardwood trees.

Solid Core – Term used to describe the inner layers of paneling or plywood that has no voids, gaps, or open irregularities and whose grain runs perpendicular to the to the outer piles. Also, a term used for a flush door with no voids between the skins often used in entries as a fire-resistant door.

Solid Moulding – This is a piece of moulding produced from a single piece of wood opposed to finger-jointed pieces.

Southern Yellow Pine – A species of trees composed of Loblolly, Longleaf, Shortleaf, and Slash Pines. The Southern Yellow Pine region extends from Texas to Virginia.

Spruce-Fir-Pine (SPF) – These three Canadian woods are grouped, marketed and sold together because of their similarities. SPF species are easy to work with and very often used in general construction. They are white to pale in color. (White Woods)

Stand - A community of trees sufficiently uniform in species, age, arrangement or condition to be distinguishable as a group from the forest or other growth on the area.

Starch - Sugar is stored in a tree as starch, which is a complex carbohydrate. This is an available energy source.

Stewardship - The concept of responsible caretaking; the concept is based on the premise that we do not own resources, but are managers of resources and are responsible to future generations for their condition.

Sturd-I-Floor – A registered trade name given by the American Plywood Association for a tongue and grooved plywood panel specifically designed for use as a sub-floor in residential construction. It is available in several thicknesses.

Sustained Yield - A method of forest management that calls for an approximate balance between net growth and amount harvested.

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Textured 1-11 (T 1-11) – A registered trade name given by the American Plywood Association for textured siding panels with grooves spaced equidistant apart along the face.

Thinning - The process of removing excess and poorer quality trees from a stand for the purpose of improving the growth and value of the remaining crop trees.

Tongue and Groove – Lumber machined on the edges to have a protruding tongue on one side with a machined groove on the other to form a snug fit when placed side by side other pieces with the same machined edges. The tongue fits into the groove.

Tree Farm - A privately owned woodland where sustainable forest management is the primary objective.

Turpentine –This is a paper making by-product commonly used as paint thinner and solvent.

Twist – This distortion is distinguished by the turning or winding of the edges of a board so that the four corners of any face are no longer on the same plane.

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Undercourse - Shingles used for the initial layer (usually low grade shingles) on a double-coursed sidewall of a building.

Understory - The layer formed by the crowns of smaller tree in a forest.

Uneven-aged Stand Management - The practice of managing a forest for various age classes, by periodically selecting and harvesting individual trees based on age.


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V – Usually used when referring to V-Groove, this is often seen in tongue and grooved pieces of lumber. Edges are often chamfered where pieces are placed edge to edge. Also, a V-groove is also machined on the face of a piece of lumber to provide decoration.

Vapor Barrier – A plastic or paper sheet, or paint, or any barrier placed on the warm side of a wall to prevent the movement of vapor through the wall.

Vertical Grain (VG) – Lumber that is sawn at 45 to 90 degree angles to the growth rings. The growth rings are close to perpendicular to the surface of the piece of lumber. VG is often used in flooring because of the durability.

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Wainscot – A lower wall surface that is different than the upper wall surface. This usually extends three to four feet from the floor up. This is the lower portion of the wall that is a contrast to the upper portion of the wall.

Wane – This refers to barked or lack of wood on the edge of a piece of lumber. Or in plywood the thin to open areas in the veneer sheets that are a result from bark or irregularities.

Warp – Any variation from the surface plane of a piece of lumber including, but not limiting, any bows, crooks, or cups in the lumber.

Western Red Cedar – A soft wood, found in the upper north west of the U.S. and parts of Canada, is straight grained and resistant to rot, decay and insect damage. This species, thuja plicata, is used extensively for roof coverings, decks, fences, exterior sidings and other outdoor applications.


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Z Flashing – A metal flashing, shaped like a Z, applied between plywood panels to shed water.

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