A building requires assembling different materials through the process of construction. Some of these materials include concrete, timber (wood), steel and glass and so on. Energy is involved in the extraction of these raw materials, their processing and transportation from the factory to the construction site and their eventual placement in most of the developing countries.
There is a general dependence on fossil fuel for energy generation for these processes. This results in the emission of greenhouse gases such as carbon dioxide, sulphur dioxide, methane etc in the atmosphere resulting in the depletion of ozone layer thus causing global warming and by extension, climate change.
Fewer trees mean more carbon dioxide in the atmosphere since plants absorb carbon dioxide and release oxygen into the atmosphere during photosynthesis. This has engendered the need to investigate the potentials of building materials that are comparatively sustainable. The potentials of timber as a building material in India with a view to determining its comparative sustainability against other commonly used building materials is higher as per the qualities and potential of timber.
QUALITIES OF TIMBER
The qualities of timber as a building material include availability, physical and aesthetic qualities, workability and versatility, environmental sustainability, flexibility of space arrangement, dry construction, industrial production and comparative cost effectiveness .(Gregory, 1984; Nolan, 1994 and Whitelaw, 1990).
Availability and Acceptability : Timber is locally available in India. It can be purchased from local suppliers and transported to site using even small vehicles. Timber is accepted as an attractive building material in most cultures.
Physical and Aesthetic Qualities : Timber has a high strength to weight ratio making it an attractive framing material. Some species are highly resistant to rot. Timber withstands humidity with less structural change than other building materials. It is very durable and there are numerous finishes available to protect and enhance the natural beauty of the material. These sealants and protective finishes promote its durability. If well protected and well installed, timber can last for centuries with minimum maintenance (Sturges, 1991).
Workability and Versatility : Timber can easily be shaped by simple hand tools. It can be cut, planed easily. There are many ways to connect timber to timber or to other materials since timber can easily be secured or fastened with nail, screws, bolts and other connectors. There are many design options possible with wood that are not practical with inorganic materials such as concrete or steel. The design performance required by a particular building application can be more flexibly matched by selecting timber of the appropriate density, compressive and tensile strength, color, texture and fire resistance (Anderson, 1970).
Environmental Sustainability : Environmental sustainability recognizes that human activity over time and the health of the environment are interdependent and that environmental health has necessary social, political and economic determinants. Probably the most significant environmental benefit of timber is its renewability and biodegradability (Resource Assessment Commission, RAC, 1991). It has low manufacturing process energy and benign air emissions (Townsend and Wagner, 2000). Timber is an excellent insulator against hot or cold weather. The old ‘’log-house’’ remains a model for minimum energy consumption in buildings (Ogunsote, 1993).
Flexibility of Space Arrangement : Partitions made from timber can easily be moved around to change layout in response to new functional requirements.
Dry Construction : Unlike concrete floors, timber floors do not require a curing period before achieving maximum strength. Construction is therefore faster. Finishing is also faster, since timber walls can be painted immediately, unlike plastered walls which require several days to dry.
Industrial Production : Timber is especially well suited for mass production. Standard components such as doors, windows, boards for walling construction, floor, ceiling and roof tiles as well as skirting can be purchased in standard sizes.
Comparative Cost Effectiveness : The local availability of high quality wood and the abundance of local millers make timber production less dependent on imports. Prices are relatively stable, since they are less influenced by the volatile foreign currency exchange market. This gives timber a cost-comparative advantage over other materials that have high import content.
Fire : The greatest challenge of wood as a structural material has been fire. Studies have shown that wood as a building material is the only material that insulates itself after the initial charring Studies have shown that when timber burns, it gets momentarily protected by its own charring, which creates an insulating charcoal layer that reduces the speed of spread of fire. This means that a timber structure, if well designed, will remain capable of carrying the load it has been designed for, even when exposed to fire for a reasonable time for evacuation. However, the best control in timber building as with other buildings is prevention in the first place and the use of fire rated timber in places that are susceptible to fire outbreak.
Weathering and Decay : Another factor that affects timber is weathering and decay. Timber decay arises from fungal attack in combination with excessive moisture, while weathering occurs as a result of chemical and light reactions (William, 1983).These effects of weathering can be prevented through the application of coatings on the surface of the timber. The choice of coating is dependent upon what is expected to be achieved. Coatings are classified into two; there are those that form a thin layer or coating on the surface of the timber while the second type provides protection.
Timber is especially well suited for mass production. Standard components such as doors, windows, boards for walling construction, floor, ceiling and roof tiles as well as skirting can be purchased in standard sizes.
through penetration without leaving any coating. However, the protective benefits of all coatings also depend on proper maintenance of the coating. No coating will last indefinitely and all need to be periodically reapplied.
AUTHOR: S. C. Sahoo, Scientist, Indian Plywood Industries Research &Training Institute, (IPIRTI)