Module 7 - Timber

Timber

Wood that has been processed into beams and planks for construction or engineering purposes.

Softwoods

Wood from needle-leaved conifers (gymnosperms) that usually grows faster and is commonly used for structural framing.

Hardwoods

Wood from broad-leaved deciduous trees (angiosperms) that typically has a more complex structure and is used for finishes or furniture.

Sapwood

The living outer layer of a tree that transports sap and stores food; it is generally lighter in color and less durable than heartwood.

Heartwood

The inactive inner core of a tree that provides structural support and is more resistant to decay and insect attack.

Cambium

A microscopic layer of reproductive tissue located between the inner bark and the wood where new cell growth occurs.

Pith

The small, soft core at the center of the tree trunk around which the first growth takes place.

Annual Rings

Concentric layers of wood produced during one growth season, used to determine the age of a tree and environmental conditions.

Earlywood (Springwood)

Wood formed at the beginning of the growing season, characterized by large, thin-walled cells and lower density.

Latewood (Summerwood)

Wood formed later in the season with smaller, thicker-walled cells that provide significantly more strength.

Cellulose

The primary structural component of wood cell walls that provides tensile strength and axial stiffness.

Lignin

A complex organic polymer that acts as the "glue" or binder to hold cellulose fibers together.

Anisotropy

The property of wood where physical and mechanical characteristics differ significantly depending on the direction of the grain (Longitudinal, Radial, or Tangential).

Moisture Content (MC)

The ratio of the weight of water in a wood sample to its oven-dry weight, expressed as a percentage.

Free Water

Liquid water found within the cell cavities (lumens) of wood.

Bound Water

Water that is chemically or physically absorbed within the cell walls of the wood.

Fiber Saturation Point (FSP)

The moisture content (roughly 25% to 30%) where cell cavities are empty of free water but cell walls are fully saturated with bound water.

Dimensional Stability Rule

Wood only begins to shrink or swell when its moisture content changes below the Fiber Saturation Point.

Tangential Shrinkage

Shrinkage occurring along the direction of the growth rings; it is the largest and most significant form of wood shrinkage.

Radial Shrinkage

Shrinkage occurring across the growth rings, typically measuring about half the magnitude of tangential shrinkage.

Longitudinal Shrinkage

Shrinkage along the length of the wood fibers; it is minimal (0.1% to 0.2%) and usually ignored in structural design.

Equilibrium Moisture Content (EMC)

The moisture level wood eventually reaches when exposed to a specific temperature and humidity in its environment.

Seasoning

The controlled process of reducing wood's moisture content to improve stability, strength, and resistance to decay.

Air Drying

A seasoning method where lumber is stacked in open air to dry naturally, which is slow but consumes little energy.

Kiln Drying

A seasoning process using a heated chamber with controlled humidity to dry lumber more rapidly and uniformly.

Lumber Grading

The classification of wood based on its strength (structural grading) or its appearance (appearance grading).

Knot

A defect formed by the base of a branch embedded in the tree trunk, which interrupts grain flow and reduces tensile strength.

Check

A seasoning defect involving a lengthwise separation of wood that typically extends across the annual growth rings.

Shake

A structural defect characterized by a separation of wood fibers along or between the annual growth rings.

Wayne

The presence of bark or the lack of wood on the edge or corner of a piece of lumber. Areas where the lumber has been cut too closely to the edge of the log and there is bark on the boards.

Warp

Any dimensional distortion in lumber (such as bow, crook, twist, or cup) caused by uneven shrinkage during seasoning.

Plywood

An engineered wood panel made of thin veneers glued together with alternating grain directions to provide dimensional stability and strength.

Glulam (Glued Laminated Timber)

A structural member made of multiple layers of dimensional lumber bonded with moisture-resistant adhesives, with the grain of all layers running parallel.

CLT (Cross-Laminated Timber)

Large engineered panels made of layers of lumber stacked and glued perpendicularly, used for structural walls and floors.

LVL (Laminated Veneer Lumber)

A high-strength engineered product made of thin wood veneers glued with the grain parallel to the long axis, used for beams and headers.

OSB (Oriented Strand Board)

An engineered panel made of wood strands or flakes oriented in specific directions and bonded with resin under heat and pressure.

Directional Strength Ratio

Crucial engineering fact that wood is 20 to 40 times stronger when loaded parallel to the grain than perpendicular to it.

Preservative Treatment

The application of chemicals to wood to protect it from decay-producing fungi and wood-boring insects.

Creosote

An oil-borne preservative distilled from coal tar, used for heavy-duty industrial applications like railroad ties and marine pilings.

Water-Borne Preservatives

Odorless and paintable chemical treatments (like CCA) commonly used for residential lumber and general construction

Humid

Low dimensional stability produces expansion in ________ environments

Dry

Low dimensional stability produces contraction in _____ environments.

Stud

Lumber used for load bearing and stud walls. (2" × 4" and 2" × 6”-dimension)

15%

Air drying reduces moisture by up to _____

Bark Pockets

______ is formed when the bark is wholly or partially encased in wood

Marine Boring Organisms

Damage by _________ in the oceans is principally caused by shipworms, pholads, Limnoria, and Sphaeroma. These organisms are almost totally confined to salt or brackish waters.