WOOD
“Crisscrossing light wood frame recalls Gothic
and surrounding trees while lifting the mind skyward.”
E. Fay Jones and Associates.
• Strong & Stiff
• Light
• Easily worked / shaped
• Fastened quickly & economically
• Recyclable
• Biodegradable
• Renewable Resource
 Not perfectly straight nor precise
 Size & shape affected by moisture
 Contains growth defects
 Can spilt & warp
 Burns easily
 Decays
 Susceptible to Insect Damage
Softwoods come from coniferous trees which are
evergreen (do not lose their leaves), needle-leaved,
cone-bearing trees.
Softwoods also grow faster than hardwoods and are
therefore less expensive.
 This type of timber is produced from broad leaf trees that
lose their leaves in winter – a deciduous tree.
 Hardwood is more dense than softwood and scratches less
easily, and usually is harder though not allways. For
example balsa is used for modelling, it is a hard wood but it
is one of the softest timbers to work with.
 Various defects which are likely to occur in
timber may be grouped into the following three:
(i) Due to natural forces
(ii) Due to defective seasoning and conversions.
(iii) Due to attack by fungi and insects.
(i) Defects due to Natural Forces: The following
defects are caused by natural forces:
(a) Knots (b) Shakes
(c) Wind cracks (d) Upsets
 (a) Knots: When a tree grows, many of its branches
fall and the stump of these branches in the trunk is
covered. In the sawn pieces of timber the stump of
fallen branches appear as knots. Knots are dark and
hard pieces. Grains are distorted in this portion.
Figure 1.9 shows some varieties of knots. If the knot
is intact with surrounding wood, it is called live knot.
If it is not held firmly it is dead knot.

 The essential difference between the wood from
hardwoods and softwoods is the presence of vessels in
hardwoods as shown in the above diagrams. These are
continuous pipes running the length of the tree and serve
as conduits for water and nutrients in the outer layers of
wood in a growing tree. In hardwoods, the cells are closed
and cannot function as conduits.
In softwoods, the cells have openings to other cells. This
means the cells are the nutrient conduits. The actual cells
in the softwood species have the same function as the
vessels in hardwoods. The open cell structure of
softwoods makes them generally more receptive than
hardwoods to preservative treatments to enhance
durability.
 Shakes: The shakes are cracks in the timber which
appear due to excessive heat, frost or twisting due
to wind during the growth of a tree. Depending
upon the shape and the positions shakes can be
classified as star shake, cup shake, ring shakes
and heart shakes.
Defects due to Defective Seasoning and Conversion: If
seasoning is not uniform, the converted timber may warp
and twist in various directions. Sometimes honey
combining and even cracks appear. This type of defects
are more susceptible in case of kiln seasoning.
In the process of converting timber to commercial sizes
and shapes the following types of defects are likely to
airse: chip marks, torn grain etc.
 Fungal Attack causes wood to decay, resulting in loss
 of weight and strength
 Fungi are parasitic plants whose spores cause the cells
to collapse
 Certain conditions are necessary for fungi to develop
i.e. low cold temperature and especially a high
moisture content.
 This is a sponge like fungus and is the most common
in timber.
 It thrives in unventilated situations where there is a
lack of circulated air.
 It is known as dry rot as it reduces the wood to a dry
soft powdery condition.
 Dangerous in buildings because of the speed it can
spread.
 Spread by wind and animals and even penetrate
masonry.
 Timber subjected to alternate wetness and dryness
begins to decompose. Outside wood is vulnerable
 The timber becomes spongy when wet and brittle
when dry
 Unlike dry rot it does not spread so it can cut back and
replaced.
 Generally affect warmer climates
 Termites
 Wharf borers or weevers which affect underwater
installations.
 Pin hole borers which only attack certain types of
timber in its green state.
 Common furniture beetle known
 Death Watch beetle
 Powder Post or Lyctus Beetle
 House houg horn beetle
 Wet Rot - This is a decomposition of sap and
fibers of the living tree set up by the access of
water through wounds in the barks.
 Dry Rot - This is a decomposition of converted
timber induced by the commonest and most
destructive dry rot fungi or weeping fungus.
 Due to fungal Attack – A fungus starts its life as a
tiny seed or spore, one of millions produced at the
fruiting stage.
o Fungi are system plant organisms which live on and
attack timber causes it to rot or decay.
o Fungi can only exist in following condition:
 Air for their respiration
 Moisture
 Suitable Temperature
 Food Supplies
 Beetles 4 types of beetle
Flour like
powder
 Boarers
BOA
RS
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
 Only major renewable structural material
 Forestry Practices
 Sustainable forestry
 Clearcutting & replanting
 Mill Practices – Lumber Recovery Factor (LRF)
 Transportation
 Embodies Energy Content