WOOD

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BUILDING MATERIALS-LUMBER Definitions:

Boards: Wooden members less than 1 inch thick. Lumber: Wooden members that measure from 1 to 6

inches thick, 2 to 12 inches wide and 6 to 16 feet long. Timbers: Wooden members greater than 6 inches thick.

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Finished lumber and boards are

sized by “nominal” sizes.

The actual size is less than

the nominal size.

LUMBER-CONT.Rough sawn—nominal size

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Finished—Actual size

WOOD TERMINOLOGY

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WOOD TERMS Hard wood Soft wood Heart wood Sap wood Growth rings

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• Plain (flat) sawn

• Quarter sawn

• Board wood

• Nominal sizing

• Board foot

WOOD TERMINOLOGY HARD WOOD—SOFT WOODS

All native species of trees are divided into two classes.

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– Hard wood have broad leaves and are deciduous

– Soft woods are conifers

WOOD TERMINOLOGY--CONT. HEARTWOOD AND SAPWOOD

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• Sapwood is the outer portion that conducts sap and has the living cells.

– The thickness will vary, but usually from 1-1/2 to 2 inches on a mature tree.

• Heartwood is the inactive cells in the inner portion.

– Mineral deposits may cause darker color.

– Deposits make wood more durable.

Heart wood

Sap woodBark

WOOD TERMINOLOGY--CONT. GROWTH RINGS

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• Because the rate a tree grows change with the seasons, a cross section will show distinctive rings.

• Springwood– Inner part of the growth ring– Usually larger cavities and thin

walls

• Summerwood– Outer part of growth ring– Smaller cells and thicker walls.

• A tree grows one springwood and one summerwood ring each year.

– Used to age trees Springwood

Summerwood

WOOD TERMINOLOGY--CONT. SAWING DIRECTION

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• Plain sawn (Flat sawn)– Board is sawed “parallel” to growth rings

– Most common boards.

• Quarter sawn– Log is first quartered

– Boards are cut “perpendicular” to the grain.

– Usually must be special ordered.Were have you seen quarter sawn boards used?

WOOD TERMINOLOGY--CONT. NOMINAL SIZING

Dimensioned finished lumber is sized using what is called an nominal sizing.

The nominal size is not the finished size of the lumber—it is the rough cut size.

The finished size, what you buy, is always less than the rough cut size.

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Lumber Sizes

Rough Size (in)

Actual Size (in)

Board Feet per Foot of

Length

1 x 4 3/4 x 3-1/2 1/3

1 x 6 3/4 x 5-1/2 1/2

1 x 8 3/4 x 7-1/4 2/3

1 x 10 3/4 x 9-1/4 5/6

1 x 12 3/4 x 11-1/4 1

2 x 4 1-1/2 x 3-1/2 2/3

2 x 6 1-1/2 x 5-1/2 1

2 x 8 1-1/2 x 7-1/4 1-1/3

2 x 10 1-1/2 x 9-1/4 1-2/3

2 x 12 1-1/2 x 11-1/4 2

4 x 4 3-1/2 x 3-1/2 1-1/3

6 x 6 5-1/2 x 5-1/2 3

Cut Size — Actual Size

SOFTWOOD CONSTRUCTION LUMBER STANDARD DIMENSIONS

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Thickness (inches) Width (inches)

Nominal Dry

1 3/4

1-1/4 1

1-1/2 1-1/4

2 1-1/2

2-1/2 2

3 2-1/2

3-1/2 3

4 3-1/2

1/2 4

5+ 1/2 “ less

WOOD TERMINOLOGY--BOARD FOOT

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• In a store lumber, boards and timbers are usually sold as $/piece, but the listed price is based on a $/bf.

• Large volumes of lumber can also be purchased on a $/bf bases.

• Board foot is a volume measurement.

• Board foot is calculated using the nominal size, not the actual size.

WOOD TERMINOLOGY--CONT.BOARD FOOT

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Bf =length (ft) x width (in) x depth (in)

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or

Bf =length (in) x width (in) x depth (in)

144

Equations:

• A board foot is a volume of lumber for a board that is one (1) inch thick, twelve (12) inches wide and twelve (12) inches long.

• One board foot = 144 in3

• Nominal sizes are used to calculate board feet when calculating costs.• Actual sizes are used when calculating loads or strength.

WOOD TERMINOLOGY--CONT.BOARD FOOT EXAMPLE

Determine the number of board feet for the following list of dimensioned lumber. 2 - 2 x 4 x 12 3 - 1 x 4 x 10 2 - 4 x 4 x 8

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Bf =length (ft) x width (in) x depth (in)

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= 2 x12 x 4 x 2

12 16 Bf

= 3 x 10 x 4 x 1

12 10 Bf

= 2 x 8 x 4 x 4

12 21.33 Bf

16 + 10 + 21.33 = 47.33 Bf

WOOD CHARACTERISTICS

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EIGHT (8) CHARACTERISTICS OF WOOD

1 Defects2 Grain orientation

a) Stiffnessb) Load bearing capabilitiesc) Fastener holding ability

3 Ease of working4 Paint holding ability5 Decay resistance

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CHARACTERISTICS—DEFECTS--STRUCTURAL

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Cross grain crack

Shake

Wane (Bark)

Split

Sloping grain

Knot

CHARACTERISTICS—DEFECTS--DIMENSIONAL

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CHARACTERISTICS—GRAIN ORIENTATION

Grain orientation is important for three reasons.

1 The direction of the grain affects the amount of deflection that occurs when loads are applied.

2 Load bearing ability.3 The orientation of fasters with the gain can

increase or decrease splitting when installing fasteners.

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CHARACTERISTICS - GRAIN ORIENTATION - STIFFNESS

Stiffness is a measure of the amount of deflection that occurs when a load is applied.

The amount of deflection for a load is determined by the dimensions of the member and the grain orientation.

Amount of acceptable deflection is different for each building member.

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CHARACTERISTICS - GRAIN ORIENTATION -- LOAD BEARING

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Wood is stronger when forces are applied parallel to the grain than when force is applied perpendicular to the

grain.

CHARACTERISTICS – LOAD BEARING – CONT.

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Load bearing ability of wood is determined by 6 additional factors.

1. Number of defects

2. Size of defects

3. Type of defects

4. Location of defects

5. Species

6. Density and moisture content

CHARACTERISTICS - GRAIN ORIENTATION - SPLITTING

Fasteners installed parallel to the grain of the wood will increase the chance of splitting the wood compared to fasteners installed perpendicular to the grain of the wood.

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WOOD CHARACTERISTICS-CONT.

Ease of working Tree species vary on workability and

machineability. Paint holding ability

Paint holds better on edge grain that on flat train Knots do not hold paint well The bark side of a flat sawed board will usually

hold paint better than the inner side. Decay resistance

Wood that is continuously dry or continuously wet does not decay.

Ideal decay conditions are 21-24% moisture The heartwood of some species is very decay

resistant.25

SUMMARY TABLES OF CHARACTERISTICS.

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WOOD CHARACTERISTICSSOFT WOODS

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Characteristic Strength

Kind of Wood Ease of Working

Paint Holding

Nail Holding

Heartwood Decay

Resistance Bending Stiffness

Softwoods

Cedar, inland red B A C A C C

Cedar, western red A A C A C C

Fir, Douglas C C B B A A

Fir, white B B C C B B

Hemlock, western B B B C B A

Larch, western C C A B A A

Pine, western white A A A B B B

Pine, lodge pole A A B B B B

Pine, Ponderosa A B B B C C

Pine, Southern yellow C C A B A A

Pine, sugar A A A B C C

Redwood B A B A B B

Spruce, Engelmann B B C C C C

Spruce, Sitka B B C C B A

Tamarack C B B B B B

Structures and Environment Hand Book, MWPS-1

WOOD CHARACTERISTICSHARD WOODS

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Characteristic Strength

Kind of Wood Ease of Working

Paint Holding

Nail Holding

Heartwood Decay

Resistance Bending Stiffness

Hardwoods

Ash, white C C A C A A

Birch, yellow C B A C A A

Cottonwood B B C C C B

Elm, rock C C B B A A

Hickory, true C C A C A A

Maple, hard C B A C A A

Oak, red or white C C A A A A

Walnut B C B A A A

Structures and Environment Hand Book, MWPS-1