Timber is one of the most important building materials in use today and this mainly because of its strength compared to volume ratio and its workability. Timber is divided into softwood (coniferous) and hardwood (broad leaf). This grouping is based solely on its structure.
Softwood trees characteristics include the following;
· A trunk which is very straight and cylindrical
· A crown that is narrow and pointed
· Needle like leaves
· A bank which is course and thick
· The seeds are borne in cones
· They are ever green i.e. they don’t drop all their leaves at once
Hardwood trees characteristics include the following;
· An irregular, less cylindrical trunk
· A crown that is wide rounded and contains large heavy branches
· Broad leaves
· The bark varies widely. It can be very smooth and thin to very course and thick and range from white to black
· They have covered seeds e.g. berries, corns and stored fruits
· They are mainly deciduous e.g. they shed their leaves in winter or cold season
Conversion of Timber; this is the sawing up or breaking down of the tree into various sized pieces of timber for a specific purpose. This can be done by sawing the trunk in either a tangential direction or in a radial direction (to cut surfaces of the timber in relation to the growth rings of the trees)
1. Tangential conversion. This is where timber is converted so that the annual rings meet the wider surface of the timber over at least half its width less than 45◦.
2. Radial conversion. This is where timber is converted so that the annual rings meet the wider surface of the timber throughout its width at an angle of 45◦ or more.
Timber is usually converted for various reasons and in construction, there are a number of methods used in conversion of timber and these include;
1. Through and through method; also known as slash or slab sawing. It is the simplest method and cheapest way to convert timber, with very little wastage. The majority of boards produced in this way are prone to a large amount of shrinkage and distortion.
2. Tangential method; this is used when converting timber for floor joists and beams since it produces the strongest timber. Also used for decorative purposes on timber that have distinctive annual rings e.g. pitch pine because it produces flame figuring or fiery grain.
3. Quarter method; this is the most expensive although it produces the best timber quality ideal for joinery purposes. Here, the boards have very little tendency to shrink or distort. In timber, where the medullar rays are prominent, the boards will have a figured finish e.g. figured or silver grained oak
4. Boxed Heart; this is a type of Radial sawing and is done when the heart of the tree is rotten or badly shaken. It is also known as floor board sawing as the boards produced are ideal for this purpose because they wear well and do not distort. The waste pieces of the timber are of an inferior quality but often used for fencing.