4. WOOD AND WOOD CONSTRUCTION

1. 4. WOOD AND WOOD CONSTRUCTION

3. Qualities of Wood • Strong & Stiff • Light • Easily worked / shaped • Fastened quickly & economically • Recyclable • Biodegradable • Renewable Resource

4. Undesirable Characteristics of Wood • Not perfectly straight nor precise • Size & shape affected by moisture • Contains growth defects • Can spilt & warp • Burns easily • Decays • Susceptible to Insect Damage

5. 4.1 WOOD AND WOOD CONSTRUCTION - AN OVERVIEW (CHAPTER 3 TO 7) • Tree trunk: Sectional details, tree types, nature of wood, composition of wood (Chapter 3) • Lumber : Sizing, Types, Defects, Seasoning, Surfacing, Grading, Wood products, Building components, Decay of wood & Preservation of wood by chemical and other treatments • Wood fasteners • Heavy Timber Frame Construction (Chapter 4) • Problems associated with heavy timber frame construction • Wood Light Frame Construction (Chapter 5) • Balloon and platform frames - Seven steps in building the frame • Exterior Finishes for Wood Light Frame Construction (Chapter 6) • Roofing and problems, Low and steep slope roofs, Paints and coatings, Sidings • Interior Finishes for Wood Light Frame Construction (Chapter 7) • Thermal insulation, vapor retarder & mechanics of their behaviors, Finish stairs

6. 4.2 CHARACTERISTIC FEATURES OF A TREE AND ITS SECTIONS • Details of the cross-section:Sapwood, heartwood, bark, cambium, summer wood, spring wood, annual rings, pith, fiber cells, growth directions (radial and tangential), rays. • Type of trees:Softwoods(Coniferous - Firs, Spruces, Pines, Hemlocks, Larches, etc.)&Hardwoods(Deciduous - Ash, Birch, Cherry, Mahagony, Oak, Teak, Poplar , etc.) • Composition of wood:Cellulose (Softwood 40-50%, Hardwood 40-50%), Hemi-cellulose (20%, 15-35%), lignin (25-33%, 16-25%), extraneous materials (5-10%, 5-10%)

7. Tree Composition • Bark • Cambium • Sapwood • Heartwood • Pith

8. Tree Cells • Primarily Hollow, Cylindrical Cells • Axis running parallel to the tree (grain direction) • Tough Cellulose bound by Lignin • Impacts the properties of wood

9. Tree Growth • Springwood (earlywood) • Faster growth • Cells larger and less dense • Summerwood (latewood) • Slower growth • Cells smaller and denser

10. Types of Trees / Woods Oak Pine Oak Pine Poplar Poplar

11. Construction Uses for Wood • Structural Framing • Subfloors and Roof Sheathing • Siding - Structural & Exposed • Finish cabinetry and Trim

12. 4.3 LUMBER • Sizing of Lumber:Sawing (plain, quarter, typical sawing) • Types:Sawn, seasoned and surfaced • Defects in Lumber:Due to growth (natural) [Knots, knot holes, shakes, wanes, decay, pitch pockets, insect and fungal damage] - Due to manufacturing and seasoning (warp, checks, crook, bow, cup, twist, wane, check, shake) • Seasoning:Moisture content in green wood, drying of wood, free water, bound water, fiber saturation point, shrinkage (radial, tangential, depends on position in trunk), seasoned wood • Surfacing:Un-surfaced, surfaced (S4S, S2S), (S-DRY, S-GRN) • Grading:For different usage, structural grade lumber (#1, #2, #3,#4, etc.). Dimension lumber, Blocking, Appearance lumber - Based on strength - Dimension of lumber (1”x2”, 2”x10”, etc.) - Nominal and actual dimensions - Boards

13. Lumber Production - Sawing • Plain Sawing • Maximum Yield • Varying grain pattern • Common use - Framing lumber

14. Lumber Production - Sawing • Quarter Sawing • Perpendicular to annual rings • Less yield, but consistent grain pattern • Improved wearing quality, less distortion

15. Typical Sawing Method

16. Lumber Drying • Drying Methods • Air • Kiln • Drying Effects • Shrinkage • Reduced weight • Increase of strength and stiffness • More dimensional stable

17. Differential Shrinkage (between radial & tangential) during drying can cause distortions

18. Lumber Surfacing Rough sawn (not surfaced) • Purpose; • Smooth • Dimensional precision • Designations; S2S, S4S • Surfacing typically performed before or after drying? S4S

19. Lumber Defects • Growth defects • Knots & knot holes • Decay and/or insect damage • Manufacturing Defects • Splits & checks • Crook, bow, • Cup, and/or twist

22. Lumber Grade & Species Graded by: • Strength & Stiffness (Structural Lumber), or • Appearance (Finish Lumber) Lumber sold by - Species and Grade • Better Grade  Higher price • Scarce or Higher Quality Species Higher price • Considerations Affecting Strength • Primary Considerations: • Species • Grade • Direction of Load Vs. Grain • Other Factors: • Length & Time of Maximum Loading • Temperature & Moisture Conditions • Size & Shape • Chemical Treatments

23. Panel Standards & Grading • Established by American Plywood Association (APA) • Standards based on; • Structural adequacy • Dimensional Stability • Durability of Adhesive

24. Structural Ratings • Specified by Thickness or Span Rating • Span Rating • Grade Stamp • For veneered & nonveneered • Long dimension perpendicular to the support

25. Exposure Durability Classifications • Exposure Durability • Exterior - siding or continuous exposure • Exposure I; waterproof glue but lower quality veneers • Exposure II; protected environments & minimum wetting

26. 4.4 WOOD PRODUCTS • Need:(a) To produce any desired shape in wood: (b) To reduce wastage of wood when members are reduced to required size • Laminated Wood: Glulam:Used for building any shape such as arch, frame, shell, etc. - Produced by joining together many small pieces of wood - Any shape can be produced: Such as curves, angles, varying width cross-sections, etc. - Seasoning of wooden pieces carried out before laminating • Structural Composite Lumber:Made of ordinary plywood veneers - Grains of all veneers oriented in the longitudinal direction to achieve maximum strength - Two types: Laminated Veneer Lumber (LVL): uses veneers in sheets and looks like a plywood with no cross-bands - Parallel Strand Lumber (PSL): Veneers are sliced into narrow strands, coated with adhesive, oriented longitudinally and pressed into rectangular cross sections.

27. Laminated Wood

28. Veneered Panels - Plywood • Thin layers of veneer glued together • Odd number of veneers • Alternating direction of veneers • Face veneers parallel • Size: 4’x8’ panels • Thickness: ¼” to 1”

29. Structural Composite Lumber (PSL)

30. 4.4 WOOD PRODUCTS(Cont’d) • Structural Wood Panel Products:Usually 4’X8’; equal in strength in two perpendicular directions; shrinking, checking and splitting greatly reduced; panels have least wastage of wood -Two main types: Veneered and non Veneered panels - Veneered panels are called structural wood panels:(1) Plywood panel -Veneers on face run in the same direction - Interiors veneers run in perpendicular directions - Odd number of veneers used, viz., 3,5,7,9, etc.(2) Composite panel:Two parallel face veneers bonded to a of core reconstituted wood. The other type isNon-veneered panel: (1) Oriented Strand Board (OSB)- Made of long, strand-like wood particles compressed and glued into three to five layers - Strands are oriented in the same direction in each layer - OSB is much stronger and stiffer than others;(2) Water Board - Composed of large wafer-like flakes of wood, which are compressed and bonded; and(3) Particle Board- Made of smaller wood particles, compressed and bonded into panels.

31. Veneer Grades • Based on the smoothness & integrity of the veneers • Classifications; A, B, C (plugged), C, D • Price Variances C Plugged C Grade A Grade

32. Non-veneered Panels • Oriented Strand Board (OSB) • Waferboard • Particleboard • Fiberboard Fiberboard Particleboard

33. Oriented Strand Board (OSB) • Long strand like wood particles • Alternate grain orientation (3-5 layers) • Compressed / glued • Strongest of the Non-veneered • Uses; Sheathing for floor, roofs, & siding

34. Waferboard & Particleboard • Waferboard • Large wafer-like particles - No orientation • Uses; Low moisture areas • Particleboard • Small wood particles • No orientation • Uses; Low moisture areas

35. 4.4 WOOD PRODUCTS(Cont’d) • Manufactured Building Components:(1) Trusses:Designed and fabricated with 2x4s and 2x6s joined together with plate connectors;(2) I - joists; (3) Panel components: Framed panels - Stressed-skin panels - sandwich panels • Other Wood Panel Products:(1) Hardwood- A thin , dense panel made of highly compressed wood fibers - Available in several thickness - Used in residential siding and roofing; (2) Cane fiber boards:Thick, low-density board with some thermal insulation properties - Used as a non-structural or semi-structural wall sheathing - Used for carpet under-layment

36. Wood Polymer Composite Planks • Advantages: • Decay Resistance • Easy Workability

37. Why Use Trusses or I-Beams? • Less material (less weight) • More efficient use of wood • Increased Span • Increased dimensional stability • Installation savings (labor)

38. Trusses • Types of Trusses - Floor & Roof Roof Trusses Floor Trusses

39. I-Beams • Uses • Sizes • Composition • Cost

40. 4.4 WOOD PRODUCTS(Cont’d) • Logs are soaked in water to soften the wood and rotated in a large lathe against a stationary knife that slices continuous strips of veneer - Then it is cut into sheets, passed through a drying kiln to reduce the moisture content to 5% - then assembles into very large sheets and cut to size, graded, and sorted according to quality • Veneer Grades: A,B,C,D,E, etc. - Size 4’x8’ and 1/4” to 1” thick - Exposure durability classification: Exterior, Exposure 1, Exposure 2, etc.

41. 4.5 DECAY OF WOOD • Some species have heart woods that have natural resistance against decay or insects (termites); they are cedars, redwood, cypress, black walnut - to be fully effective the wood must be 100% heartwood • Wood can be attacked by fungi (microscopic plants) that cause decay, molds and stains. Fungi develop in woods when the moisture in wood is above 20%, the temperature are mild (40o to 100o F ), sufficient oxygen and sufficient amount of wood as food. • “Dry” and “Wet” rots cause decay. Even though dry rot grows even in the absence of sufficient amounts of moisture, yet originally it grew as a result of alternate wetting and drying. Wood in the ground is exposed to moisture, oxygen, and rather a mild temperature; hence major decay occurs in this area. Wood submerged in water does not undergo decay, since adequate supply of oxygen is not available

42. 4.5 DECAY OF WOOD(Cont’d) • A harmless type of fungi, called ‘white pocket’ is found living in softwood trees. It is an acceptable defect in wood. • Molds and stains are also caused by fungi, but they do not damage the wood - In appearance lumber, staining and molds are undesirable. • Insects bore holes and damage the lumber. When structural integrity is important, then do not use wood damaged by insects. Termites living in subterranean nests, get into the wood and start eating the cellulose in wood. Put a ceramic shield - Remove all wood scraps around the construction site - Treat the soil chemically - Use chemically treated, pressure impregnated wood for sills, posts and other parts near the soil - Use concrete foundation around wood

43. 4.6 PRESERVATION OF WOOD FROM FUNGI, INSECT AND FIRE • Wood treated by pressure and non-pressure methods • Pressure treatment involves impregnation of wood with desired preservatives under high pressures. Non-pressure processes are brushing, dipping, cold soaking, and diffusion (thermal and vacuum) • Major preservatives are: - Pentachlorophenol and creosote (used for piles, utility poles, etc.) - Oil-borne pesticideWater-borne preservative: Inorganic Arsenic (ammoniacal copper arsenate, chromated copper arsenate, ammoniacal copper zinc arsenate), and ACQ preservative (alkaline copper and a quarternary compound) • Fire retardant treatment: Carried out by pressure impregnating and chemical coating - Lumber is placed in a pressure vessel and impregnated under high pressures - Costly and as such used only for fire walls - Chemical treatment with zinc chloride, boric acids, sodium tetraborate, mono-diammonium phosphate • General safety measures: Wooden components should be kept dry at all times - Keep all wood well clear of soil - Ventilate attics and crawl spaces to remove all moisture - Use good construction techniques to keep wood dry - Fix roof and plumbing leaks as soon as they occur.

44. 4.7 WOOD FASTENERS • Fasteners are the weakest links in wooden construction • Earlier mortised and pegged joints were weak due to material removal • In today’s construction, nails, screws, bolts, toothed plates & adhesives are used to develop full strength of joined members. • Since most of the joints depend primarily on the bearing strength of joints, simple fasteners are found to be sufficient • Nails: Sharpened metal pins driven into wood with a hammer or mechanical gun - Should have corrosion resistance: Hot-dip galvanized - Type of nails: Common nails (flat head); used for most structural purposes - Box nails: made of lighter gauge wires; less holding power - Casing nails, finish nails and brad nails: virtually headless, used for attaching finish components of a building - Deformed shank nails: used for attaching gypsum wall boards and floor under-layment - Hardened concrete nail: provides proper holding power to soft roofing tiles - Methods of fastening: Face nail, End nail, Toe nail.

45. Nails • Sharpened metal pins • Installation: Hammer or mechanical nail gun • Common Nails • Finish Nails • Other types

46. 16d Galvanized 16d Sinker Deformed Shank 10d Galv. Spiral Finish Nail Roofing Nail (far right)

47. Nails • Size - Measured in pennies • Coatings • Bright/ Plain uncoated steel • Corrosion-resistant • Resin/Vinyl

48. Anchorage • Face, End, or Toe

49. Machine Driven Nails & Staples • Nail Guns, Staple guns • Pneumatic (or electric) • Pre-packaged fasteners (collated nails) • Improved Productivity • Used in many applications • Power actuated fasteners Battery Powered Electric Nailer Collated Nails

50. 4.7 WOOD FASTENERS(Cont’d) • Wood screws and lag screws:Inserted into drilled holes and turned into place with a screw-driver or wrench - Frequently used in cabinet & furniture construction ; as well as in hinges • Timber connectors:Split ring connectors: to increase the load carrying of bolts - Inserted in matching circular grooves - Spreads the load over a larger area • Toothed plates:Used in factory produced roof trusses - Inserted into wood with hydraulic presses • Metal plate framing devices:Used for strengthening common connections in wood - Joist/Beam hangers, Post cap & post base - Rafter anchor & framing anchor - Angles - Machine driven staples • Adhesives:Used very widely in factory-produced plywood, laminated wood, cabinet work, etc.