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- Board Foot (BF)
- A unit of lumber volume equal to 144 cubic inches (1" × 12" × 12"). The standard measurement for pricing hardwood lumber.
- Modulus of Rupture (MOR)
- The maximum bending stress a wood sample can withstand before failure, measured in psi. Higher MOR indicates stronger wood.
- Janka Hardness
- The force in pounds (lbf) required to embed a 0.444-inch steel ball to half its diameter into wood. The industry standard for comparing hardness.
- Moisture Content (MC)
- The percentage of water weight relative to oven-dry wood weight. Kiln-dried lumber typically reaches 6–8% MC.
- Quarter-sawn
- Lumber cut with annual rings at 60–90° to the face, producing straight grain, better stability, and distinctive fleck in species like oak.
- Rift-sawn
- Lumber cut with annual rings at 30–60° to the face, yielding tight, straight grain and minimal figure. Often used for consistent furniture panels.
- FAS Grade
- Firsts and Seconds — the highest standard grade in NHLA hardwood grading. Boards must yield at least 83.3% clear face cuttings.
- Specific Gravity
- The ratio of wood density to water density. A key predictor of mechanical strength; values above 1.0 mean the wood sinks in water.
- Equilibrium Moisture Content (EMC)
- The moisture content at which wood neither gains nor loses moisture to surrounding air. Varies by region and climate.
- Tangential Shrinkage
- Shrinkage parallel to the growth rings (across face-sawn boards). Typically 1.5–2× radial shrinkage; causes cupping.
- Radial Shrinkage
- Shrinkage perpendicular to growth rings. Generally less than tangential shrinkage and contributes to dimensional stability.
- T/R Ratio
- Tangential-to-radial shrinkage ratio. Values closer to 1.0 indicate more uniform movement and reduced tendency to warp or cup.
- Heartwood
- The inner, non-living wood of a tree. Typically darker, more decay-resistant, and more dimensionally stable than sapwood.
- Sapwood
- The lighter-colored outer wood that actively transports water. Generally less durable than heartwood but accepts stain more readily.
- Interlocked Grain
- Grain direction that reverses periodically between successive growth layers. Causes ribbon-stripe figure but makes planing difficult.
- Blunting Effect
- The rate at which a wood species dulls cutting tools. Silica content, density, and interlocked grain increase blunting.
- Span Rating
- The maximum distance a structural member (joist, rafter, decking) can bridge unsupported while meeting load and deflection limits.
- Live Load
- Dynamic forces on a structure from occupants, furniture, snow, or traffic. Residential decks typically require 40 psf minimum.
- Dead Load
- The permanent, static weight of the structure itself — framing, decking, railings, and fixed equipment.
- Dimensional Lumber
- Softwood lumber cut to standardized sizes (2×4, 2×6, etc.) and graded for structural use. Nominal size exceeds actual size.
- CITES
- Convention on International Trade in Endangered Species. Regulates cross-border trade of protected wood species via Appendices I, II, and III.
- Kiln-Dried (KD)
- Lumber dried in a controlled kiln to reduce moisture content below fiber saturation point, improving stability and reducing biological risk.
- Air-Dried (AD)
- Lumber dried naturally by stacking with stickers outdoors. Slower than kiln drying; final MC depends on ambient humidity.
- Fiber Saturation Point (FSP)
- The moisture content (~28–30%) at which cell walls are saturated but cell cavities are empty. Shrinkage begins below FSP.
- Spalting
- Coloration caused by fungal colonization in wood. Creates decorative zone lines and color patterns. Often found in maple and birch.