TIMBER AS A CONSTRUCTION MATERIAL IN THE BUILDING INDUSTRY.pptx

This topic deals with timber as a construction material, characteristics and use in the building industry compared to other building material

1. TIMBER Timber is one of Ghana’s most readily available natural resource where the forest occupies one third of her total area and has about 400 timber species. There are a total number of timber companies which produce timber to the required sizes in commercial quantities, such as 1x12, 2x6, 2x4, 2x3 and 2x2.

2. The choice of a material for the construction of building depends on factors such as availability of the material, the ease with which it can be worked, the speed of fabrication and erection and the tolerance it provides. It is estimated that 60% of the cost of a building account for material used in the construction. It is, therefore, regrettable to note that even though Ghana has abundant timber resources, their use in the construction of building is limited to doors, windows and roof structures.

3. Timber is a combustible material and has a greater resistance to fire than steel aluminium in a larger sections. This is because metals distort, bend and collapse in a short time when burning, while timber sections stand fires for a longer period without failure. In its natural state, timber satisfies general fire resistance requirement of building codes. With additional treatment it can be rendered incombustible. Fire is therefore not a setback in the use of timber for buildings.

4. Timber houses are durable, comfortable and also more resistant to earth quakes. Wood has excellent insulating properties and a low thermal conductivity. It is resilient, resistant to fungi and termite when treated and have proved to be more economical than steel or aluminium framed. There are no less than about 400 species of timber available in Ghana, out of which about 100 species are usable for construction. Of these, about 40 are commercialized and 14 primarily for export.

5. Wood is made of the individual units, called cells. When the cells of the same type are together and perform the same functions, their formation is described as tissue. The growth of tree is as a result of the living process of cells formation. The grain of wood is the direction or arrangement of fibers or cells. The strength of timber varies with the angle of inclination of applied stress to the direction of the grain.

6. Trees are divided into two groups: Softwood (coniferous) known botanically as Angiosperm and hard wood (broad-leaf) as Gymnosperm. The soft wood has the following characteristics:

7. They are mainly evergreen They have needle-like leave It is light in weight Annual rings are very distinct It is comparatively weaker and splits easily. Some examples are pines, firs, spruces etc.

8. Hardwoods on the other hand, are the densest, strongest and most durable timber. They have the following characteristics: They have broad leaves They are deciduous The wood is comparatively heavier

9. Comparatively darker in colour . The annual rings are not distinct. It contains a large percentage of acid. It is hard and difficult to work upon. Examples of hardwoods are teak, oak, iroko , mahogany, sapele , danta etc.

10. Major timber production in Ghana. Annual processed volume (cubic metres ) of log, lumber and plywood. REGION LOG EXPORT IMPORT Eastern 52000 1500 20000 Western 290000 103000 31000 Brong Ahafo 85000 31000 10000 Ashanti 278000 76000 40000 TOTAL 705000 211500 101000 Source : Forest Products Research Institute.

11. Cross section of a tree trunk Bark: the outer layer of the providing protection to the tree from knocks and other damage. Bast : the inner bark carries enriched sap from leaves to the cells where growth takes place.

12. Cambium : layer of living cells between the bast and the sapwood . Crown: The branches and leaves provide typical summer shade. Heartwood : mature timber no longer carries sap - the heart of the tree provides the strength of the tree, usually a distinctive darker colour than the sapwood. Medullary rays: food storage cells radiating from the medulla Sapwood ; the new growth of a tree that carries the raw sap up to the leaves. Trunk ; the main structure of the tree. Root structure ; the root absorbs water and minerals from the soil. It is the anchor of the tree .

13.   Conversion of timber Large trees in the forest are felled by hand axe or chain saws. The felled tree trunk is converted into logs by sawing off all branches. They are then converted to sizes. Conversion is therefore a method of sawing logs into standard size, such as plants or boards. Some basic methods of conversion of logs are: Sawing (flat sawn, quarter cut) Peeling – for producing sheet of plywood Sharing – (thin decorative veneers)

14. Seasoning of timber Timber in its green state is not suitable for wood work because of the presence of water in the cavities of the cells. Most of this moisture must be removed to avert any excessive shrinkage which would cause defects in the work and a tendency to decay. Removal of the moisture will increase the strength, durability and resilience of the timber. It becomes lighter in weight, more workable, unlikely to twist/warp and make it immune to decay and insect attack.

15. Methods of seasoning There are two basic methods of seasoning a timber: Air seasoning (Natural) Kiln seasoning (artificial)

16. Advantages It is economical It needs less attention Disadvantages The process is lengthy Timber stack can be attacked by insects.

17. ARTIFICIAL Because of the great length of time required and sufficient low moisture content of wood cannot be achieved for natural dry season, artificial seasoning is largely used today. In kiln season the rate of drying is accelerated by heating and control of humidity. This is accomplished in a closed chamber with controlled temperatures, humidity and air flow.

18. Advantages The seasoning period is shorter Seasoning defects and infestation are control Disadvantages It is expensive Greater care and skill required

19. Properties of timber There are two main properties of timber. These include; Physical properties Mechanical properties

20. The physical properties of timber include; Aesthetic appearance Strong and lightweight Flexibility

21. The mechanical properties of timber include; Durability Fire resistance Thermal conductivity

22. Material Thermal conductivity Thermal resistance (R) Efficiency as insulator Wood 0.80 1.25 100.00 Air space 1.03 0.97 77.6 Common brick 5.0 0.20 16.0 Facing brick 9.0 0.11 8.9 Concrete 12.0 0.08 6.4 Stone 12.5 0.08 6.4 Steel 312.0 0.0032 0.25 Aluminum 1415.0 0.00070 0.06 Thermal properties.