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Wood and Plastics. Major Topics. Classification of Wood Hardwood Softwood Growth of Wood Wood Defects Wood (Lumber) Seasoning/Kiln Drying Moisture Content Cutting. Major Topics con’t. Wood (Lumber) Decay/Insects Grading Sizing (Nominal vs. Actual) Joints Fasteners

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Wood and Plastics

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Wood and Plastics

Major Topics

  • Classification of Wood

    • Hardwood

    • Softwood

  • Growth of Wood

  • Wood Defects

  • Wood (Lumber)

    • Seasoning/Kiln Drying

    • Moisture Content

    • Cutting

Major Topics con’t

  • Wood (Lumber)

    • Decay/Insects

    • Grading

    • Sizing (Nominal vs. Actual)

    • Joints

    • Fasteners

  • Prefabricated Wood (Glue-laminated)

Major Topics con’t

  • Plywood

  • Other Panels

    • Waferboard

    • Composite

    • Particleboard

    • OSB (Oriented Strand Board)

  • Plastics

Classification of Wood

  • Hardwood – trees which are deciduous (shed broad shaped leaves annually) ex: Birch, Ash, Maple, Oak

    • Uses: flooring, interior paneling, cabinets & furniture

  • Softwood – trees which are evergreen (needle-like leaves) ex: Southern Pine, Fir, Spruce, Redwood

    • 75% of lumber produced is made of softwood

    • Uses: structural framing lumber, sheathing, roofing, and exterior siding

Growth of Wood

  • Growth is formed from core (pith) in rings. The # of rings and spacing between rings show age and growing conditions of tree.

  • Wood is made of hollow tubular cells running parallel to the long axis of the tree.

Wood Defects

  • Common defects include: knots, stain, pitch pockets, decay, and cracks.

  • These defects will impact the visual “grading” of wood products

Examples of Defects

Wane – irregular rounding caused by cutting too close to outside of log


Resin Pocket


  • Broad term that applies to all finished or semi-finished wood shaped with parallel longitudinal surfaces

  • Nominal piece sizing includes:

    • Board -- 11/2” or less thick and 2” or more wide

    • Dimension – 2” to 5” thick and >2” wide

    • Timbers -- 5” or more thick and wide

Lumber Measured in “Board Feet”


See page 330 Section for explanation on how to calculate board feet

Pop Quiz – provide answers to the following:

  • What is the standard unit of measure for lumber?

  • Calculate the board feet in a 2” x 4” stud 8’-0 long

  • Find the board feet in 60 pieces of 2” x 10” joists 14 feet long.

Pop Quiz Answers

1.Board feet

2.(Thickness [in] x Width [in] x Length [in])/144 = Board Feet

(2 x 4 x [8 x 12])/144 = Board feet

(8 x 96)/144 = Board feet

(768)/144 = Board feet

5.3 Board feet (rounded off)


Thickness (in) x Width (ft) x Length (ft) = Board Feet

2 x 4/12 x 8 = Board feet

2 x .333 x 8 = Board feet

5.3 Board Feet (rounded off)

3.Number of pieces x Thickness (in) x Width (ft) x Length (ft) = Board Feet

60 x 2 x 10/12 x 14 = Board feet

60 x 2 x .833333 x 14 = Board feet

1400 = Board feet

Often written as 1.4 MBM [1.4 Thousand Board Measure]

Seasoning/Kiln Drying

  • Seasoning- the process of reducing moisture until a suitable level is achieved (causes shrinking in lumber size)

  • May be seasoned in the air (2-6 months for softwood and may take 4 years for some hardwoods) or by using a kiln

  • A chemical (hygroscopic) may be applied to the wood to keep surface moist to reduce shrinkage cracks (checks)

Moisture Content

  • The strength of wood increases as the moisture content (m.c.) decreases

  • M.C. varies depending on the conditions (geographical region & indoor/outdoor) in which the lumber will be used

  • Typically, m.c. does not exceed 19%


  • Plain-sawed (flat sawed) – lumber which is cut in parallel slides [less waste & cheaper; warps & splits]

  • Edge-sawed – lumber which is cut perpendicular to the exterior of the tree

  • Quarter-sawed – lumber in which the log is 1st cut into quarters and then cut on the diagonal [produces the most attractive wood grains]


  • Termites – destroy wood by chewing it (chemical or physical barriers should be used to deter them)

  • Fungi – feed on wood fibers leaving wood weakened with rotting

  • Avoid placing untreated wood directly in contact with concrete

Pressure-Treated Lumber

  • Must meet all EPA (Environmental Protection Agency) requirements

  • CCA (Chromated Copper Arsenate) was the most widely used until Dec. 2003 –no longer produced because of environmental concerns

  • The current wood preservatives include:

    • ACQ (alkaline copper quat)

    • Copper Azole (CA types A & B)

    • Sodium Borate (SBX)

      **** Main concern with new products are that they increase the deterioration of fasteners drastically more than CCA did – reduce the life expectancy of a structure by a factor of four

Source: CSI March 2004 publication of The Construction Specifier


  • Depends on the appearance ( # of defects) and strength

  • Lumber pieces are marked with a grade stamp

    • Typical stamp includes

      • Grading body (WWP – Western Wood Products

      • Mill identification

      • Grade name (Const – construction)

      • Moisture content

      • Type of wood (D-Fir – Douglas Fir)

        • See Figs. 6.2-20,-21, and -22 – on pages 335-36 for examples of grade marks

Sizing (Nominal vs. Actual)

  • Lumber is referred to by nominal size but the actual size is less (see lumber sizes handout)

    • 2”x4” actually measures 1-1/2” x 3-½”

    • 1” x 8” actually measures ¾” x 7-1/4”



  • Nails, screws, bolts, staples, anchors, and joist hangers are common fasteners

  • Sizes, styles, and finishes (coatings) depend on the intended application

  • Length of nails designated in “pennies” [d]


See page 361 for Figures 6.6-2

and 6.6-3

**** There are a variety of nailing methods used:

Toe nailing, end nailing, face nailing, blind nailing

**** Standard sizes of common wire nails

Prefabricated Wood

  • Because of the limitations of size of sawn wood – the gluing of smaller pieces together will enable structural members of virtually any length, cross-section, and desired curves to be made

  • Glu-lam members are widely used in areas of construction using arches (must comply with ANSI 190.1)

GlueLams [Laminated Timbers]See page 405

  • Individual laminations are placed so that:

    • Weak spots are separated from each other to avoid concentration of weakness

    • Appearance flaws in wood are hidden within the member

    • End joints between lams are separated from each other to avoid a plane of weakness

    • The strongest wood is placed where stresses are highest

Species of Lumber Used for GlueLam

  • Douglas Fir

  • Alaska Cedar

  • Spruce-Pine Fir

  • Southern Pine


  • Plywood is a type of glued, laminated wood. Thin wood layers of laminations are arranged with the grains of each layer perpendicular to the adjacent one.

  • Veneers – the actual laminations consisting of face & back, crossbands, and the inner (core) Usually an odd number of veneers (3-5; may be up to 11)

  • Thickness may range from ¼” – 1 ¼”

Advantages of Plywood vs. Sawn Lumber

  • Has great transverse strength which aids in strengthening/bracing entire structure when used over studs, joists, and rafters for wood frame construction

  • Less warping and change due to moisture changes

  • Is more easily bent to form curves for concrete forms or curved wood construction

  • Fabricated in large sheets (4’x8’, typical) which covers larger areas more quickly

  • Can be worked closer to the edges without splitting

  • Desired appearance can be obtained by using thin veneers of high quality wood where they are visible

Grades/Types of Plywood

  • 5 basic grades from best to less desirable finished appearance: A, B, C, C plugged, & D [see figs 6.3-5;6 and 6.3-6 on pages 340-2 for grades]

  • 5 species groups (according to stiffness and strength): Group 1 is the strongest/stiffest

  • Types of plywood: interior and exterior

    • Interior- made with glue suitable for indoor use; available in any grade

    • Exterior – made with hot, phenolic resin glue which is unaffected by water & resists weathering; no veneers below C grade used

APA – Engineered Wood Products

  • APA – American Plywood Association – key organization for plywood information

  • Website link:


Other Panels

  • Waferboard

  • Composite

  • Particleboard

  • OSB (Oriented Strand Board)


  • Usually contain synthetic resins. May also contain plasticizers, fillers, and colorants

  • 2 basic classes of plastics; thermoplastics (no chemical change during heating/cooling) & thermosetting plastics (change chemically when heated and solidify while still hot)

  • Plastic products are strong, light in weight, formable, and resistant to corrosion




  • Construction Materials and Processes, 3rd Edition. Watson, Don A.. McGraw-Hill, 1986. Imprint 2000. ISBN: 0-07-068476-6

  • Construction Principles, Materials, and Methods, Seventh Edition. H. Leslie Simmons, John Wiley and Sons, Inc., 2001.

  • Olin’s Construction Principles, Materials, and Methods, Eighth Edition. H. Leslie Simmons, John Wiley and Sons, Inc., 2007

  • Architectural Materials for Construction, Rosen, Harold J. and Heineman, Tom. McGraw-Hill, 1996. ISBN: 0-07-053741-0

  • Basic Construction Materials, 6th Edition. Marotta, Theodore W. Prentice Hall, 2002. ISBN: 0-13-089625-X

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