Wood: Naturally better
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 the same. 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 fulfill both form-and-function requirements. Technical research on Malaysia's timber species done by the Forest Research Institute Malaysia has contributed significantly to how different timber species can be dried, treated and processes/utilised.
This section:
- Addresses the common concerns that surround the proper usage of wood by explaining why wood behaves as it does.
- Lists the green credentials of wood and its inherent advantages over other building materials.
- Explains how specifying timber, particularly from certified and/or legal sources, actually contributes to forest conservation and climate change mitigation.
The Nature of Wood
Wood is a Biological Material
Wood is made up of cells, which tend to be elongated and are 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 noncellulosic 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's moisture content changes depending on its surrounding. The temperature and humidity of the surrounding atmosphere and the amount of water already in the wood will determine whether wood absorbs or loses water vapour. These absorptions or losses in water vapour will cause the wood to swell or shrink. The anisotropic nature of wood will cause unequal 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.
Advances in R&D by many research agencies globally have contributed to a rich and growing repository of knowledge on timbers which have led to the development of various treatments and techniques as well as engineering solutions to manage timber's natural properties that will enhance its usage, and improve recovery rate thus less wastages.
Wood is made up of cells, which tend to be elongated and are 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 noncellulosic 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's moisture content changes depending on its surrounding. The temperature and humidity of the surrounding atmosphere and the amount of water already in the wood will determine whether wood absorbs or loses water vapour. These absorptions or losses in water vapour will cause the wood to swell or shrink. The anisotropic nature of wood will cause unequal 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.
Advances in R&D by many research agencies globally have contributed to a rich and growing repository of knowledge on timbers which have led to the development of various treatments and techniques as well as engineering solutions to manage timber's natural properties that will enhance its usage, and improve recovery rate thus less wastages.
Positive Attributes of Wood
Strength
Wood has a high strength-to-weight ratio, i.e., 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.
Modern engineered timber products like Glued Laminated Timber (Glulam) and Cross Laminated Timber (CLT) allow wood to be used in constructing high-rise buildings. Currently, the world's tallest timber building is a 14-storey apartment called Treet in Bergen, Norway. In the pipeline are plans to build a 34-storey timber building in Canada.
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 require treatment when used under harsh conditions, many species of timbers can naturally last for a very long time.
Timber can be treated to make it harder, termite resistant or weather-resistant. Treatment can be done by impregnating wood with certain chemicals which are effective yet safe for use by humans. This process is widely available and is affordable. Treated timber will often out-last naturally durable timbers.
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.
Wood has a high strength-to-weight ratio, i.e., 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.
Modern engineered timber products like Glued Laminated Timber (Glulam) and Cross Laminated Timber (CLT) allow wood to be used in constructing high-rise buildings. Currently, the world's tallest timber building is a 14-storey apartment called Treet in Bergen, Norway. In the pipeline are plans to build a 34-storey timber building in Canada.
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 require treatment when used under harsh conditions, many species of timbers can naturally last for a very long time.
Timber can be treated to make it harder, termite resistant or weather-resistant. Treatment can be done by impregnating wood with certain chemicals which are effective yet safe for use by humans. This process is widely available and is affordable. Treated timber will often out-last naturally durable timbers.
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 to 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 the timber. The slow rate of burn 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.
The speed and ease of ignition is dependent on the rate of accumulation of heat at the surface of the wood. Several factors influence this rate and they are the size of the piece of wood, the rate of heat loss from the surface, the presence of thin outstanding edges and the rate which heat is supplied to the surface of the wood. Small pieces with sharp projecting edges such as matches , ignite easily. On the other hand, large pieces, with round edges, like a round Glulam column catch fire at a much slower rate. In buildings with engineered timber panels, heat does not conduct from one side of the panel to the other.
Research has shown that timber used as structures such as columns in large buildings, performs better during a fire compared to 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 the timber. The slow rate of burn 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.
The speed and ease of ignition is dependent on the rate of accumulation of heat at the surface of the wood. Several factors influence this rate and they are the size of the piece of wood, the rate of heat loss from the surface, the presence of thin outstanding edges and the rate which heat is supplied to the surface of the wood. Small pieces with sharp projecting edges such as matches , ignite easily. On the other hand, large pieces, with round edges, like a round Glulam column catch fire at a much slower rate. In buildings with engineered timber panels, heat does not conduct from one side of the panel to the other.
Case Study: Timber's Performance in an Actual Fire
Shortly before midnight on 31 December 2012, a fire started in a strip mall in Salem, Oregon. The fire spread fast and destroyed everything, except for the Glulam beams the building was designed around. Post-fire, the Glulam beams were still so sound that crews had to use their backhoes and bulldozers to physically break the beams in half to get them down.
Glulam beams consistently outperform other leading materials in fire resistance tests. The average building-fire temperature ranges from 700° to 900° Celsius. Steel weakens dramatically as its temperature climbs above 230° Celsius, retaining only 10% of its strength at about 750° Celsius. Wood will not ignite until it reaches almost 260° Celsius. Once heavy timber ignites, it chars at a slow rate of 0.635 mm per minute*. The slowness of burn is due to the inherent property of wood to naturally insulate in a fire. Thus, in a 30-minute fire, only 19 mm of each exposed surface of the Glulam is lost to charring, leaving most of the original cross section intact.
Unprotected metals lose their strength quickly in a fire and often collapse suddenly due to their rapid loss of strength. Studies have shown that within 10 minutes of a fire starting, steel loses its structural properties by over 50%, while Glulam still holds over 80% of its strength. Actually, no building is fire-proof since most fires start with the structure's contents. The goal of fire-resistive construction is to provide occupants adequate time to evacuate the structure safely.
*under the American ASTM E-119 fire exposure.
Source: American Institute of Timber Construction.
Steel weakens dramatically as its temperature climbs above 230° Celsius, retaining only 10% of its strength at about 750° Celsius. Wood will not ignite until it reaches almost 260° Celsius.
Shortly before midnight on 31 December 2012, a fire started in a strip mall in Salem, Oregon. The fire spread fast and destroyed everything, except for the Glulam beams the building was designed around. Post-fire, the Glulam beams were still so sound that crews had to use their backhoes and bulldozers to physically break the beams in half to get them down.
Glulam beams consistently outperform other leading materials in fire resistance tests. The average building-fire temperature ranges from 700° to 900° Celsius. Steel weakens dramatically as its temperature climbs above 230° Celsius, retaining only 10% of its strength at about 750° Celsius. Wood will not ignite until it reaches almost 260° Celsius. Once heavy timber ignites, it chars at a slow rate of 0.635 mm per minute*. The slowness of burn is due to the inherent property of wood to naturally insulate in a fire. Thus, in a 30-minute fire, only 19 mm of each exposed surface of the Glulam is lost to charring, leaving most of the original cross section intact.
Unprotected metals lose their strength quickly in a fire and often collapse suddenly due to their rapid loss of strength. Studies have shown that within 10 minutes of a fire starting, steel loses its structural properties by over 50%, while Glulam still holds over 80% of its strength. Actually, no building is fire-proof since most fires start with the structure's contents. The goal of fire-resistive construction is to provide occupants adequate time to evacuate the structure safely.
*under the American ASTM E-119 fire exposure.
Source: American Institute of Timber Construction.
Steel weakens dramatically as its temperature climbs above 230° Celsius, retaining only 10% of its strength at about 750° Celsius. Wood will not ignite until it reaches almost 260° Celsius.
Green Credentials of Wood
Carbon Sequestration
Wood and CO2 are natural partners. Trees absorb CO2 as they grow, so the more trees 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 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 results in much lower CO2 emissions. No other mainstream building material does this.
Climate Change Mitigation
Using timber that comes from sustainably 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 will 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. Therefore, it is better to harvest the bigger trees rather than let them die and rot, to keep the carbon imprisoned in the wood.
Sustainability
Timber is the 'greenest' and only truly renewable building material. New trees can be planted to replace those that were harvested, thus ensuring a perpetual supply of timber. Moreover, the planting and harvesting of trees contribute positively to the health of the environment through the cycle of "absorb-and-lock" of CO2 in the atmosphere.
Wood and CO2 are natural partners. Trees absorb CO2 as they grow, so the more trees 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 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 results in much lower CO2 emissions. No other mainstream building material does this.
Climate Change Mitigation
Using timber that comes from sustainably 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 will 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. Therefore, it is better to harvest the bigger trees rather than let them die and rot, to keep the carbon imprisoned in the wood.
Sustainability
Timber is the 'greenest' and only truly renewable building material. New trees can be planted to replace those that were harvested, thus ensuring a perpetual supply of timber. Moreover, the planting and harvesting of trees contribute positively to the health of the environment through the cycle of "absorb-and-lock" of CO2 in the atmosphere.
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 used in another project. The recovered timber can be resized and reshaped to cater to other uses.
Timber Scores Well in A Life Cycle Assessment
Life Cycle Assessment (LCA) is a technique to assess environmental impacts associated with all the stages of a product's life cycle from cradle to grave(i.e., from raw material extraction through materials processing, manufacture, distribution, use, repair and maintenance, and disposal or recycling). LCA research by renowned entities such as the UN's FAO (2002), the UK Building Research Establishment (2002), the US Consortium for Research on Renewable Materials (2004) and the American Hardwood Export Council (2012) have all shown timber's cradle-to-grave ecological quotient to be superior to that of steel, concrete and plastics.
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 used in another project. The recovered timber can be resized and reshaped to cater to other uses.
Timber Scores Well in A Life Cycle Assessment
Life Cycle Assessment (LCA) is a technique to assess environmental impacts associated with all the stages of a product's life cycle from cradle to grave(i.e., from raw material extraction through materials processing, manufacture, distribution, use, repair and maintenance, and disposal or recycling). LCA research by renowned entities such as the UN's FAO (2002), the UK Building Research Establishment (2002), the US Consortium for Research on Renewable Materials (2004) and the American Hardwood Export Council (2012) have all shown timber's cradle-to-grave ecological quotient to be superior to that of steel, concrete and plastics.
Reducing CO2 Through Sustainable Timber Harvesting
