Wood

Terminology and Classification

The terms wood, lumber, and timber are often used

interchangeably, but each term has a distinct meaning.

Wood Hard fibrous substance lying beneath the bark of trees.

Lumber Wood that has been sawn into construction members.

Timber Lumber that is five inches or larger in its least dimension.

Terminology and Classification

Wood is classified as softwood or hardwood depending on the type of tree it originates from.

Softwoods, such as pine, fir, and spruce, come from needle-leaved conifers, which are evergreen

Hardwoods, such as maple, oak, and sycamore, come from broad-leaved deciduous trees, which shed their leaves annually.

The important difference between softwoods and hardwoods is botanical, which refers to the cellular structure of the two groups. Most hardwoods are in fact harder than softwoods; however balsa wood, one of the softest woods known is actually a hardwood.

Characteristics of Wood

Wood consists of approximately 70% cellulose and 18% to 28% lignin, which is the adhesive imparting strength to the wood.

The remainder is made up of minerals and extractives, which give wood its color, odor, and resistance to decay.

Cutting and Sawing Lumber

Lumber can be cut from a log in two different ways: tangent to the annual rings, called plain-sawed in hardwoods and flat-grained or slain-grained in softwoods.

Lumber cut radially to the annual rings is called quarter-sawed in hardwoods, and edge-grained or vertical-grained in softwoods.

Lumber is classified as quarter-sawed if the grain is 45 degrees to 90 degrees to the wide face and plain-sawed if the grain is 0 degrees to 45 degrees to the wide face.

PLAIN SAWNED LUMBER AND TIMBER

QUARTER SAWNED LUMBER AND TIMBER

Cutting and Sawing Lumber

Characteristics of plain-sawed lumber include:

1. Distinct grain pattern,

2. May twist, cup, or wear unevenly,

3. Tends to have a raised grain,

4. Shrinks and swells more in width, less in thickness,

5. Less waste in cutting, and therefore less expensive.

Cutting and Sawing Lumber

Characteristics of quarter-sawed lumber include:

1. Relatively even grain pattern,

2. Wears evenly with less warpage,

3. Shrinks and swells more in thickness, less in width,

4. More waste in cutting and therefore more costly.

Shrinkage, distortion, and warpage of lumber depends partially on the way lumber is cut from a tree. Wood shrinks most in the direction of the annual growth rings (tangentially); less across these rings (radially); and very little parallel to the grain (longitudinally).

As moisture content in the cells of wood changes, particularly as it dries out, wood members can change shape if the change moisture content is not done in controlled conditions. As wood dries out the amount of shrinkage differs in various directions.

Shrinkage is limited to parallel to the grain of the wood. It is greatest when measured in a tangent to the growth rings. The amount of shrinkage along the radius of the wood is less than that tangentially. Depending on where in the log the member is cut from, uncontrolled drying can cause wood members to exhibit unusual shapes as shown here in this exaggerated illustration.

Seasoning of Wood

shrinkage stiffness strength

Making wood suitable for construction involved more than simply cutting down a tree and sawing the wood to size. Wood in a tree is green, that is, contains a large amount of water. If green lumber is used in construction, it will shrink as it dries out.

Seasoning of Wood

shrinkage stiffness strength appearance

Making wood suitable for construction involved more than simply cutting down a tree and sawing the wood to size. Wood in a tree is green, that is, contains a large amount of water. If green lumber is used in construction, it will shrink as it dries out.

To minimize shrinkage, lumber should be seasoned dried before use to between10% to 20% moisture content. This can be accomplished by air drying, which takes several weeks or kiln drying.which takes only a few days. Over 90% of lumber is kiln dried

Framing lumber is considered seasoned if its moisture content is 19% or less.

An 18’ 2x10 loses approx 5 gallons of waterHardwood Inc.Tour Tuesday, Sept. 6, 2011

Drying Lumber Video 1:39 minutes

Wood Defects

Variety of defects affect the

strength

appearance

use

and grading of lumber.

Defects may be natural.

damaged by insects decayed by fungus

and of course, destroyed by fire.

or caused by manufacturing

Wood Defects

NATURAL DEFECTS:

Knot: branch embedded in a tree and cut through manufacturing.

Shake: pitted area sometimes found in cedar and cypress.

Pitched Pocket: opening between growth rings and containing resin.

Wood Defects

MANUFACTURED DEFECTS:

Check: lengthwise grain separation caused by seasoning.

Split: lengthwise separation of wood extending from one face to another.

Wane: lack of wood on the edge or corner.

Warp: shrinkage distortion of a plane surface, includes---bow, crook, cup and twist.

Pressure Treating Lumber Video 1:01 minutes

Wood can be damaged by insects and decayed by fungus

Standardized terms and dimensions

Standardize Dimensions – Nominal Verse Actual size

Plywood Veneer

Cutting

forms parallel pattern

forms repeating pattern

forms random pattern

Sample Plain Sliced Patterns

Sample Quarter Cut Patterns

Miscellaneous Panels

random matching

slip matching

book matching

running match

balance match

center match

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• Every other veneer turned over

• Veneer joints match, creating symmetrical pattern

• Most common

• Used with plain slicing most

Book Match

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• Leaves “slipped” off in sequence without turning

• Repeating grain - joints don’t match

• Often used with quartered or rift veneers

Slip Match

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• Veneer book broken• Leaf sequence

destroyed on purpose

• Appearance of boards

• Casual or Rustic• More difficult than

Book or Slip

Random Match

T = Tension

C= Compression

Wood is generally stronger in compression than tension. Unlike other materials, the strength of wood is not the same in every direction for tension and compression.

Wood is stronger when the load is applied parallel to the grain than perpendicular to the grain. In fact, the strength of wood in tension perpendicular to the grain is so low that this type of loading can easily cause the wood to split.

For shear, wood is very strong perpendicular to the grain and relatively weak parallel to the grain. Therefore, horizontal shear stress (parallel to the grain) is often a design consideration, while vertical shear stress (perpendicular to the grain) is not.

What is Southern Pine? Video 1:00 minute

Wood Species

Wood Species Guide

• http://www.hardwoodweb.com/lumber/rfq/quotes.cfm?do=guide

Example of what we will see at tour:

Purpleheart Lumber Sources Includes species in tropical regions of Central America and South America.

Appearance Generally straight grained, sometimes interlocked, with a fine even texture. Creamy white sapwood and vibrant purple heartwood that turns to dark-purplish brown with exposure to light.

Physical Properties Very heavy, hard, strong, and stiff with good decay resistance and stability in service. Steam-bends moderately well.

www.exotic-wood.com/purpleheart.htm#

Structural Strength of Wood

• Species ( Fir, Hemlock, Pine, etc)

• Grade• Direction of Grain ( parallel or perpendicular)

• Size and Shape

• Moisture Content

• Definition of Moisture Content

Weight of water compared to the weight of dry wood

• Formula for Moisture Content

Weight of water as % of wt. of dry wood

• What is considered an acceptable moisture content of framing lumber?

• What is considered an acceptable moisture content of framing lumber?

19%

Weight of the water in the wood is 19% of the weight of the dry wood. If the wood was 100 pounds dry, then it has 19 pounds of water in it.

Wood

Engineered Wood Products

• Particle Board• MDF• OSB• LVL• LSL• Masonite• Plywood• Glulam• Plastic Lumber• Wood I-Beams• Wood Trusses

Structural Wood Panels• plywood• composite panel• non-veneered panel

Particle Boardmanufactured from wood particles, such as wood

chips, sawmill shavings, or even saw dust. Made with larger pieces of wood than used to make MDF

Oriented Strand Board (OSB)sometimes called waferboard

Oriented Strand Board (OSB)

O S B Video 1:08 minutes

Medium Density Fiberboard (MDF)Combination of softwood fibers, wax & resin.

Stronger than particle board

Laminate Strand Lumber (LSL)Made up of strands of lumber instead of veneers

Laminated Veneer Lumber (LVL) LVL is made by gluing sheets of veneer together. Unlike plywood, here all

veneer layers are going in the same direction. Wide panels are manufactured to the thickness of the desired lumber. The panels are

ripped into lumber of nominal width.

Masonite

Type of hardboard invented by William H. Mason.[1] It is formed using the Mason method, using wooden chips and blasting them into long fibers with steam and then forming them into boards. The boards are then pressed and heated to form the finished

boards. No glue or other material is added.

Plywood made from thin sheets of wood veneer, called plies or

veneers, layered in opposite directions

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What is hardwood plywood?

• Three or more layers of wood or wood products laminated into a single sheet

• FACES; Outside decorative veneers

• CORE; MDF, PB, VC, Combos

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Construction balance

• Three is minimum

• Always Odd3, 5, 7, 9……

• Panel Balance a Must!

Plywood Video 2.21 minutes

• Plywood is classified as interior or exterior depending on the type of adhesive used: moisture-resistant for interior use, and water-proof for exterior use. Plywood used in construction is primarily softwood. Plywood used for interior millwork or cabinetry is usually hardwood.

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Plywood Plywood is classified as interior or exterior depending on the type of adhesive used: moisture-resistant for interior use, and water-proof for exterior use. Plywood used in construction is primarily softwood.

Plywood used for interior millwork or cabinetry is usually hardwood.

Plywood is graded according to quality of the veneer: A BestD poorest.

Span RatingFirst number - maximum recommended roof span in inches if used as roof sheathing

Second number -maximum recommended span use as subflooring.

For example, a panel identified as 32/16 can be used as roof sheathing over rafters spaced 32 inches on center or as subflooring over joists spaced 16 inches on center.

Glued Laminated Lumber (Glulam) These beams are made by gluing many boards together to form a

structural member bigger than the trees from which the board were sawn. Since the load is carried by the material in the top and bottom faces and the middle only has to resist shear, high quality lumber is used in the top

and bottom while medium grade lumber is used in the center. (gluelam or glulam) Joints between boards are typically scarf or finger joints.

Curves that remain in one plane are much easier to construct thancompound curves (a dome). A dome is likely to be segmented curves.

Glue Laminated Construction

Glulam Video 2:04 minutes

RPL Recycled Plastic LumberLumber-like products with a plastic content of 50% or more. Higher expansion & contraction with temperature changes. Less structural

strength

I-Beams & I-JoistsVeneer lumber is used for the flanges and plywood or

OSB is used for the web to resist shear.

I - Joist Video 2:48 minutes

Wood Trusses

Fink Truss

Wood Siding

end