lesson 5

• Wood


  A natural organic material that has been used for many centuries for the construction of buildings, bridges and a variety of other structures
• Wood remains an important construction material today as research and improved technology have led to a better knowledge of the material behaviour
• Timber


  • Has a warm texture and attractive appearance
  • Is often used for internal finishing as well for the main structure
  • Is easy to work with
  • Can be produced in a wide range of shapes and sizes
• Characteristics for Sustainability of Timber

  • Durability
  • Strength
  • Permeability
  • Toughness
  • Elasticity
  • Workability
  • Hardness
  • Fire resistance
  • Shape
  • Smell
• Durability


  The ability to withstand the effects of chemical agents, biological elements, and physical forces
• Strength


  The ability to take pressure and loads acting on it, varies depending on the direction
• Permeability


  The timber should not absorb more than 8 to 12 % of water when submerged
• Toughness


  The ability to resist sudden vibrations and shocks
• Elasticity


  The ability to return its original shape or size once deformation causing loads are eliminated
• Workability


  How easily the timber can be cut into desired form
• Hardness


  The ability to resist penetration
• Fire resistance


  Timber exhibits a low level of fire resistance, with dense wood providing the highest resistance, up to a certain threshold. The thermal conductivity is influenced by moisture content, density, and porosity
• Shape


  Preserving the shape of timber is crucial during both cutting and seasoning processes. Poor-quality timber is prone to bowing, warping, or splitting during conversion
• Smell


  A quality timber emits a sweet fragrance, while a disagreeable or unpleasant smell is indicative of decay in the wood
• Classification of timbers

  • Exogenous trees
  • Endogenous trees
• Exogenous trees


  Trees that grow outwards and increase in bulk by the formation of successive annual rings. Timber used for building engineering works is mostly obtained from exogenous trees
• Types of Exogenous trees

  • Conifers or Evergreen Trees (Softwood)
  • Deciduous or Broad-Leaf Trees (Hardwood)
• Conifers or Evergreen Trees (Softwood)


  • Grow quickly, less dense with a simple cell structure, yield softwood, show distinct annual rings, light in color and weight, can easily split, and are resinous, comparatively weak in strength
• Deciduous or Broad-Leaf Trees (Hardwood)


  • Used for furniture, tools, and cabinetry, yield hardwood which is dark in color, hard, close-grained, and strong, useful for important engineering works
• Endogenous trees


  Trees that grow inwards in a longitudinal fibrous mass, too flexible and aren't suitable for engineering works
• Timber Properties

  • Color
  • Grain
  • Figure- patterns
  • Texture
  • Density
  • Durability
  • Shrinkage and swelling
  • Defects
• Swietenia macrophylla (Mahogany)


  Renowned globally for its capacity to yield high-quality, original timber, suitable for construction materials, plywood (veneer)