Environmental Advantages of Timber

The Environmental Advantages of Timber

Within today's day and age there are few materials that can be used for the purpose of construction and still remain sustainable. Like oil, metals we commonly use for building purposes extracted from 'terra firma' cannot be replaced once all resources are consumed. Therefore metallic based materials can know longer be implemented in place of rival sustainable products.
Timber being one of the world's rare sustainable building materials, as they reproduce when harvested. Due to timber's sustainability, through adequate management and conservation as a whole, we can ensure timber's longevity and continual purpose as an adequate building material. This objective is contained through the continual process of planting forests and plantations on a sustainable level. When comparing timber to other substitute building materials which are generally non-renewable.
During the harvesting of timber carbon atoms are stored within the tree even whilst being manufactured into timber products. If the trees being harvested are left to perish and rot as unwanted waste, the carbon within the timber transforms into carbon dioxide which is released back into the atmosphere as a harmful Green House Gas.

Hardwood -Hardwood trees are generally broadleaved trees.   These tree species are deciduous, retaining their leaves only one growing season.   The designation Hardwood trees does not necessarily relate to the hardness of the wood.. Hardwood trees are also called broad leaf trees or deciduous trees. Typical hardwood trees include ash, elms, oak, maple, walnut, hickory, mahogany, and walnut. Woods grown in tropical climates are generally hardwoods.   Hardwoods have shorter fibers compared to softwood. Some hardwoods are evergreen.

Softwoods- Softwoods are one of the botanical groups of trees that have persistent needle-like or scale-like leaves; softwoods are evergreen and have longer-length fibers than hardwoods. Softwood trees include pines, spruces, firs, cedars.

Strength of Wood- Green wood has high moisture content (generally) and this results in reduced strength.As it is dried it loses the moisture content and becomes stronger.

Wood may be described as an orthotropic material; that is, it has unique and independent mechanical properties in the directions of three mutually perpendicular axes: longitudinal, radial, and tangential.   The longitudinal axis is assumed parallel to the fiber (grain); the radial axis is normal to the growth rings (perpendicular to the grain in the radial direction); and the tangential axis is perpendicular to the grain but tangent to the growth rings.  (Think of the grain as the tree rings running up the trunk /branch - planks of wood are simply sections of the tree trunk (or branch)

Sapwood and Heartwood

The structure of a tree stem can be broadly divided into two main zones. When viewing the end-section of a log or cross-section of a tree stem, the central wood zone, is usually considerably darker than the portion adjacent to the bark. Generally, the light coloured wood is the sapwood remainder.

Appearance and physical properties

Colour- Most timbers show variation in colour between species and within species. It can also vary within a single piece. Colour descriptions usually relate to the heartwood of the species and may be significantly different from that of the sapwood. (Sapwood is always white to very light brown.) Colour can vary with use, age and by the application of finishes. Timber exposed to light will change colour, and unprotected timber exposed to the weather will eventually become silvery grey in colour.

Texture – of timber may be described as being coarse, fine, even or uneven. The differentiation between coarse and fine texture is determined by the size and arrangement of the wood cells. Softwoods are usually fine textured, while hardwoods may be either. For example, mountain ash is a coarse textured hardwood, but brush box is a fine textured hardwood. The main process affecting texture of the timber is the finishing applied during fabrication. Planing will produce a fine texture, sanding or brushing – a fine to coarse texture, rough sawing or splitting a coarse to uneven texture. Surface finishes will also affect the texture, high build; smooth coatings will give the finest texture.

Figure – refers to the pattern produced on the surface of the timber. The pattern is determined by the type of grain, the arrangement and size of cells, colour variations and sawing patterns. Designers can use these features to produce striking effects in different lights. Where particular grain patterns are required, this will need to be investigated very carefully with the supplier, and may require special milling.

Grain – refers to the general direction, size and arrangement of wood fibres. Grain can be described as sloping, straight, spiral, irregular, wavy etc.

Hardness – refers to the resistance of the timber to penetration. This is an important parameter for flooring, with harder species wearing better and requiring less maintenance than softer species. It may also be an important parameter for some cabinetry and joinery.

 Density – is influenced by cell structure and size, thickness of the cell walls and moisture content. The density of timber at specific moisture content (usually 12%) is the amount of wood substance in a given volume, expressed as kilograms per cubic metre. Density is one of the most reliable indicators of stiffness, joint strength, and hardness, ease of machining, fire resistance and drying characteristics.

·                     Thermal properties – timber is a natural insulator. Air pockets within its cellular structure make timber a natural barrier to heat and cold. As thermal conductivity increases with density, lightweight timber is a better insulator than dense timber. Thermal conductivity also varies slightly with moisture content, and natural characteristics such as checks, knots and grain. Air spaces between building elements, such as studs in a framed wall, are effective heat barriers and are considered when determining the thermal resistance of building assemblies. An advantage of timber framed construction is that additional insulating material can be placed in the spaces between framing members without increasing wall, ceiling, roof or floor thickness.

·                     Acoustic properties – an important property of timber is its ability to damp vibrations. Its cellular network of minute interlocking pores converts sound energy into heat energy by frictional and viscous resistance within these pores and by vibration of their small fibres. Because of this high internal friction, wood has more damping capacity than most other materials. This damping reduces the tendency of structures to transmit vibrations long distances and is suitable for use in applications requiring acoustic separation such as MRTFC. Timber also reduces the magnitude of resonant vibrations, so is used extensively where good acoustics are required eg concert venues, music suites, halls and meeting rooms. Some acoustic panelling may have arrangements of holes to further increase damping.

·                     Chemical resistance – timber offers considerable resistance to attack by a wide variety of chemicals including organic materials, hot or cold solutions of acid or neutral salts or dilute acids.
Resistance to chemical attack is greater in softwoods than in hardwoods. Timber is commonly used for vats and tanks for chemical storage and for structural members in factories where corrosive vapours are present.
Direct contact with caustic soda should be avoided. Strong acids and alkalis will destroy timber in time, but the process is relatively slow.

·                     Fire resistance – is influenced by density, and type of extractives. It can be enhanced by various treatments including pressure application of fire retardants or surface application of intumescent coatings. These treatments are not common, and may require special production runs. Plenty of lead time needs to be given for the supply of these products.

·                     Termite resistance – is influenced by cell size, and type of extractives. Termite resistance can be improved by treatment processes.

·                     Electrical resistance – varies greatly with moisture content. Moisture meters use this property to measure the moisture content of timber. Seasoned timber is normally regarded as a non-conductor for most practical purposes. Timber can be heated by subjecting it to a high frequency electrical field. Some adhesives can be heat cured by this process and are used in the manufacture of laminated timber and plywood.

·                     Mechanical damping – This property is important in the evaluation of vibration in structures, and in determining earthquake response. Timber itself has relatively high internal damping due to its cell structure as discussed under “Acoustic properties” above, but in normal framed construction, the large numbers of semi-flexible nailed connections lend further damping to the assembled structure.