Wood is Good
The Nature
of Wood
Wood is Good
Wood has been associated with man since time immemorial. Unfortunately, many architects, builders, contractors and specifiers shy away from using wood because of their lack of understanding of the material and the common myths and fallacies associated with wood.
One fundamental aspect of wood that must be understood is that it is a biological material and therefore subject to environmental factors that influence its formation and growth. This makes wood variable, i.e., with different densities and technical properties, so no two pieces of wood are similar. Once this tenet is understood, wood becomes a more accommodating material, lending itself to a huge variety of uses and applications, largely due to its ability to fulfil both form-and-function requirements.
The nature of wood
Wood is a biological
material
Wood is made up of cells, which tend to be elongated and arranged along the longitudinal axis of the tree trunk. These cells are made up of a complicated mixture of polymers of cellulose, interspersed with other non-cellulosic carbohydrates and lignin. These cells act as tiny elongated thin-walled tubes and impart some outstanding physical and mechanical properties to the wood.
Wood is anisotropic
Wood behaves differently along its three major differential axes in terms of strength properties and dimensional movements.
Wood is hygroscopic
Wood is subject to changes in moisture content of its surrounding. The temperature and humidity of the surrounding atmosphere and the amount of water already in the wood will determinate whether wood absorbs or loses water vapor. These absorptions or losses of water vapor will cause the wood to swell or shrink dimensional movements in the three directions.
Wood is inert
Wood is inert to the action of most chemicals. This property makes wood suited for many industrial applications where resistance to corrosion is important. When wood is exposed to atmospheric conditions, it will only erode at a rate of 0,25 inch per century. Even this can easily be prevented by applying coatings and proper treatment on the wood surface.
Positive attributes of wood
Strength
Wood has a high strength-to-weight ratio, ie., for the same strength required for a given structure, the weight of the timber material to be used can be as much as 16 times less than steel, or five times less than concrete. Weight for weight, wood can be designed to carry a heavier load than steel, i.e., one tonne of wood can carry a heavier load than one tonne of steel.
Durability
There is a great variety of timbers with a wide range of properties to suit various outdoor and internal applications, and for both aesthetic and structural purposes. While some timbers are perishable under uncontrolled conditions, many species of timber will often out-last naturally durable timbers.
Acoustic properties
Timber has good acoustic properties. It has better sound dampening capacity than most structural materials such as concrete, which reflects sounds with stronger echoes. The natural acoustic properties of timber control this excessive echo by reducing the transmission of sound vibrations.
Excellent insulator
Wood is an excellent insulating material because of the presence of the empty cell walls, which act as tiny air traps that resist the transfer of heat. This characteristic is deemed ideal for insulation materials. Compared with wood, other building materials such as bricks, steel and concrete are not good insulators.
Wood requires minimal external energy to keep a building within the thermal comfort zone of its inhabitants. Wood is six times better than brick as an insulator; eight times better than glass; 15 times better than concrete; 390 times better than steel and 1 700 times better than aluminium.
Performance in fire
Research has shown that timber used as structures, such as columns in large buildings, performs better during a fire compared with steel or concrete. This is because steel will buckle and concrete will crack and crumble very suddenly under high temperatures. Thick timber columns, on the other hand, will initially ignite but the charring of the outer layers of wood will cut off the oxygen supply and effectively slow down the burning of the deeper layers of timber.
The slow burning rate is important because it gives the occupants enough time to evacuate during a fire. Timber columns have been found to be still standing and functioning after intense fires.
Versatility
Timber is the most versatile building material compared to the other building materials. It can be used for both structural and decorative purposes, as well as for outdoor and internal applications.
The fact that trees grow according to the natural environment they are in means that there are thousands of grains and shades to choose from globally, providing an excellent choice for architects, builders and interior designers.
Energy efficient
Processing wood is energy efficient. The production of one tonne of cement requires five times more energy than the production of one tonne of wood; 14 times more energy for one tonne of glass; 24 times more energy for one tonne of steel and 126 times more energy for one tonne of aluminium.
The ‘Green’ credentials of wood
Carbon sequestration
Wood and CO2 (carbon dioxide) are natural partners. Trees absorb CO2 as they grow, so the more forest we plant, the more CO2 they can absorb. Trees play an important role in reducing carbon in the atmosphere by being part of the carbon cycle that involves the trees absorbing CO2 from the air, releasing oxygen, and storing the carbon in the wood.
However, mature trees absorb less CO2 than young trees. Harvesting mature trees will open up to the forest canopy, enabling younger trees to grow, thereby absorbing more carbon from the atmosphere.
Carbon locking
The CO2 that is absorbed by the trees as they grow remains “imprisoned” in the wood. Using wood-based material contributes to the continued imprisonment of the CO2.
Building with wood causes much lower CO2 emissions than building with conventional construction materials. No other mainstream building material does this.
Recyclability
Timber is a fully recyclable building material and it requires a fraction of the energy required to produce concrete or steel. When a building is demolished or renovated, the recovered timber can be resized and reshaped to cater for other applications.
Climate change mitigation
Using timber that comes from sustainable managed forests can actually help address climate change by reducing the amount of greenhouse gases in the atmosphere. Trees absorb CO2 as they grow, thus significantly reducing the amount of CO2 in the atmosphere. The absorbed carbon is converted into wood in the tree. However, if the forest was left totally alone, the trees in the forest would grow old and die. Trees can also die due to fire, wind damage and lightning strikes. When a tree dies, the wood will rot and release the stored carbon in the form of CO2. In order to keep the carbon imprisoned in the wood, it is better to harvest the bigger trees than to let them die and rot.