Mister End Grain
Menu

Wood flooring glossary

Updated · 22 sources · 9 min read

Quick answer

Plain-English definitions of 54 wood flooring terms, each tied to a cited source such as the USDA Wood Handbook, NWFA technical publications, FEP, European standards listings and The Wood Database. Where a term has more than one usage, the glossary says so.

This glossary explains the terms you meet when you read about wood floors. Definitions come from the sources listed at the foot of the page: mainly the USDA Forest Products Laboratory, technical publications of the US National Wood Flooring Association (NWFA), the European Parquet Federation (FEP), standards listings and The Wood Database. A few terms, such as chevron and underlay, have no standards-body definition, so they rely on named manufacturers' descriptions and say so. For deeper reading, follow the links to our guides and flooring types.

A

Acclimatisation: The process of allowing a wood floor's moisture content to equilibrate with the environment in which it will perform2. The NWFA now suggests "conditioning" is the more accurate word, because the aim is to prepare the building for the flooring rather than to alter the wood7. See our guide to moisture and acclimatisation.

Air-dried: Wood dried by exposure to air in a yard or shed, without artificial heat1.

B

Brinell hardness: A measure of resistance to indentation used for wood flooring. The 2000 edition of the European test standard EN 1534 was titled "Wood and parquet flooring – Determination of resistance to indentation (Brinell)"; the current 2020 edition is titled "Wood flooring and parquet – Determination of resistance to indentation – Test method"11. Compare Janka hardness.

C

Checking: A lengthwise separation of the wood that usually extends across the growth rings and commonly results from stresses set up during seasoning1.

Chevron: A parquet pattern whose boards form a "V" formation, as Kährs describes it19. BOEN describes its chevron as laid at a precise 60-degree angle16. See chevron flooring.

Click joint: A glueless joint system. Kährs says it introduced the first parquet floor with its glueless Woodloc® joint in 199921, and BOEN lists a "5G Click connection" on its planks17.

Compression set: A permanent narrowing or crushing of the board edges that occurs when boards swell after a substantial moisture increase while adjacent boards stop them expanding2.

Cupping: A concave or dished appearance of a board, with the edges raised above the centre, caused by a moisture imbalance through the thickness of the board, where the bottom is wetter than the top2. See also warp and crowning.

Crowning: The opposite of cupping: a convex appearance with the centre of the board higher than the edges, caused when the top of the board is wetter than the bottom2.

D

Dimensional stability: The degree to which a piece of wood maintains its manufactured dimensions when temperature and humidity change2.

E

Earlywood and latewood: The two parts of a growth ring. Earlywood forms early in the growing season and is usually less dense and weaker; latewood forms after it and is usually denser and stronger1.

End grain: Wood cut so the growth rings face up, a transverse cut2. The NWFA notes that end-grain blocks are sometimes classified among parquet patterns3. See end grain flooring.

End-lift: Board ends that appear raised. The NWFA says this is very common with engineered flooring that has experienced an increase in moisture2.

Engineered wood flooring: In the NWFA definition, real wood from top to bottom, normally made from multiple veneers or slats of wood glued together at opposing directions. "Composite engineered" flooring has real wood on the wearable surface only, with a backing or core of any composite material6. See engineered wood flooring.

Equilibrium moisture content (EMC): The moisture content at which wood neither gains nor loses moisture when surrounded by air at a given temperature and relative humidity21.

Expansion gap: Space left around the perimeter and at fixed obstructions so the floor can move. The NWFA installation guidelines give a minimum of ½ in. (12.7 mm) for parquet and a general rule of ¾ in. for solid strip and plank, and refer engineered floors to the manufacturer's recommendation4. Always follow the maker's instructions.

F

Fibre saturation point: The stage at which cell walls are saturated and cell cavities are free of water, usually taken as about 30% moisture content, based on oven-dry weight1.

Figure: The pattern produced in a wood surface by growth rings, rays, knots, deviations from regular grain such as interlocked and wavy grain, and irregular colouring1.

Flat-sawn: See plain-sawn.

Fuming: Using ammonia vapour to darken wood. The fumes react with the natural tannins in certain species, and woods high in tannin, such as white oak, beech and butternut, respond best13.

G

Gaps (seasonal): Separations between solid wood boards that open in winter when heated air lowers relative humidity. The NWFA calls them a normal phenomenon, says most close when humidity returns, and advises against filling them2.

Grade: A designation of the quality of a manufactured piece of wood or of logs1. Makers use their own scales: BOEN, for example, groups its gradings as Calm, Lively and Rustic15.

Grain: The direction, size, arrangement, appearance or quality of the fibres in wood. The term has a specific meaning only when qualified, as in straight grain or cross grain1.

Growth ring: The layer of wood added to a tree during a single growing season1.

H

Hardwax oil: A floor finish based on plant oils and natural waxes. BOEN describes its Live Natural oil as containing sunflower, thistle or soya bean oil with carnauba and candelilla waxes14. Kährs notes that an oiled finish enhances the texture and grain of the wood19. See our guide to wood floor finishes.

Hardwood: Wood from broad-leaved trees, botanically angiosperms. The term does not necessarily refer to the actual hardness of the wood2.

Heartwood: The wood extending from the pith to the sapwood, whose cells no longer take part in the tree's life processes. It is usually darker than sapwood2.

Herringbone: Rectangular boards laid in a zig-zag so that they meet in a "point"20. The NWFA lists herringbone among geometric parquet patterns and notes that subfloor flatness is especially critical for it, typically within ⅛ in. over 10 feet3. See herringbone flooring.

Hygroscopic: Able to absorb and retain moisture, or give it up. Wood and wood products expand as they absorb moisture and become smaller as they lose it2.

J

Janka hardness: A measure of how well a wood resists denting. The figure is the force in pounds-force (lbf) or newtons (N) needed to embed a 0.444 in. (11.28 mm) steel ball into the wood to half the ball's diameter, normally on wood dried to 12% moisture content8. See Janka hardness explained and the hardness chart.

K

Kiln-dried: Wood dried in a kiln, a chamber with controlled airflow, temperature and relative humidity, using artificial heat1.

Knot: The portion of a branch or limb that has been surrounded by subsequent growth of the stem1.

L

Laminate flooring: In the USDA glossary, a paper-based laminate is a multilayered panel made by compressing sheets of resin-impregnated paper into a solid mass1. This differs from engineered wood flooring, which the NWFA defines as real wood from top to bottom6.

Live-sawn: A method of sawing straight through the log's diameter, leaving in the heart of the log and the grain variations found in all grades of lumber2.

M

Medullary rays: Strips of cells running from the bark toward the centre of the tree. Because they run perpendicular to the grain, they can add visual interest to finished flooring depending on how boards are cut2.

Moisture content: The weight of the water in the wood expressed as a percentage of the weight of the wood itself2. The USDA expresses it as a percentage of the oven-dry weight1.

Moisture meter: A tool for rapid determination of moisture content in wood by electrical means, in two main types: pinless (dielectric) and pin-type (electrical resistance)2.

P

Parquet: A term with a trade definition and a pattern meaning. For FEP, a product can be called parquet only if its real wood top layer is at least 2.5 mm thick, as set by European standard EN 137569; EN 13756 is itself the terminology standard for wood flooring and parquet12. The NWFA describes parquet as typically made of individual pickets assembled into panels held together by wire, mesh, tape or paperface3.

Plain-sawn (flat-sawn): Flooring cut so that the growth rings are mostly parallel, at 0° to 45°, to the wide face of the board, a tangential cut2. The USDA gives the same under 45° threshold for flat grain1.

Plank and strip: The NWFA treats solid strip flooring as less than 3 in. wide and solid plank flooring as 3 in. wide or more when setting moisture tolerances2. See wide plank flooring.

Q

Quarter-sawn: Flooring cut so that the growth rings are mostly perpendicular, at 45° to 90°, to the wide face of the board, a radial cut2. The USDA lists quartersawn as another term for edge-grained lumber1.

R

Refinishing: Sanding and recoating a floor to renew it. FEP's refinishable programme identifies parquet whose wear or top layers are thick enough to be refinished, based on a minimum 2.5 mm real wood top layer10. See sanding and refinishing.

Relative humidity: The ratio of the water vapour in the air to the amount the air would hold at saturation at the same temperature, usually expressed as a percentage2.

Rift-sawn: Flooring cut neither parallel nor perpendicular to the growth rings, so that the rings make angles of 30° to 60° to the board face; also called bastard sawn2.

S

Sapwood: The active wood near the outside of the tree, usually lighter in colour than heartwood2. The USDA adds that it is more susceptible to decay under most conditions1.

Shrinkage and swelling: A change in dimension due to a loss of moisture below the fibre saturation point (shrinkage), or a gain in moisture below it (swelling)2.

Solid wood flooring: Flooring made from a single piece of wood sawn into boards or strips. Kährs notes that it expands and contracts with seasonal humidity, which makes it less format-stable than engineered flooring19. See solid wood flooring.

Subfloor: The base the flooring is fixed or bonded to. The NWFA says wood subfloors must be flat, clean, dry, structurally sound, free of squeaks and free of protruding fasteners5. For solid strip flooring under 3 in. wide, it advises no more than 4% moisture content difference between acclimated flooring and subfloor5.

T

Tongue and groove: A kind of machined edge joint in which boards interlock along their edges1.

U

Underlay: A layer laid between subfloor and floor. BOEN's guide ties underlay to a floor that feels quiet, stable and comfortable, and lists moisture barrier, impact sound and footfall sound among its functions18. See installation methods.

V

Veneer: A thin layer or sheet of wood. The USDA distinguishes rotary-cut veneer, cut on a lathe, from sawn veneer, produced by sawing1.

Versailles panel: A pre-assembled square parquet panel. Havwoods describes the pattern as squares held together by what appears to be an interwoven mesh of wood strips, and says it takes its name from the Palace de Versailles22. See Versailles panels.

W

Warp: Any variation from a true or plane surface. The USDA says warp includes bow, crook, cup and twist, or any combination of them1.

Wear layer: The real wood layer at the top of an engineered or parquet board. In the NWFA definition of a wood floor, real wood is the top-most, wearable surface6; see also parquet for the 2.5 mm minimum9.

Sources

  1. Wood handbook: Wood as an engineering material (FPL-GTR-282), Glossary, USDA Forest Service, Forest Products Laboratory. Accessed .
  2. Moisture and Wood, Technical Publication No. A100 (2nd edition, 2017), National Wood Flooring Association. Accessed .
  3. Ornamental Floors: Design and Installation, Technical Publication No. B300 (3rd edition, 2015), National Wood Flooring Association. Accessed .
  4. NWFA Guide 4: Installation Guidelines (revised 02.2016), National Wood Flooring Association. Accessed .
  5. NWFA Guide 3: Subfloor Guidelines (revised 02.2016), National Wood Flooring Association. Accessed .
  6. Real wood definition, National Wood Flooring Association. Accessed .
  7. Rethink Acclimation, Hardwood Floors magazine (NWFA). Accessed .
  8. Janka Hardness, The Wood Database. Accessed .
  9. Professionals, FEP, the European Parquet Federation. Accessed .
  10. Parquet Refinishable Program, FEP, the European Parquet Federation. Accessed .
  11. NF EN 1534: Wood flooring, determination of resistance to indentation, test method, AFNOR. Accessed .
  12. NF EN 13756: Wood flooring and parquet, terminology, AFNOR. Accessed .
  13. Fuming Wood with Ammonia, Fine Woodworking. Accessed .
  14. Surface treatments, BOEN. Accessed .
  15. Grading systems, BOEN. Accessed .
  16. Exquisite, BOEN. Accessed .
  17. Plank 138 Oak White (product page), BOEN. Accessed .
  18. Floor underlay, BOEN. Accessed .
  19. Wood flooring, Kährs. Accessed .
  20. Herringbone flooring, Kährs. Accessed .
  21. Our history, Kährs. Accessed .
  22. Versailles and other panels, Havwoods. Accessed .