Friday, 20 August 2010

Construction

In all parts of the developed world, construction is highly controlled. Building codes and regulations, regularly updated to ever more exating standards, specify the materials and methods that are regarded as suitable for safe construction, particularly in terms of fire resistance and stability.In response to such legislation, the construction industry has typically reacted by enhancing the performance of structural elements: one example of this is the treating of lumber with chemicals to promote fire- and moisture-resistance. However, for anyone who is concerned about the environment, treating wood with potentially toxic chemicals to overcome such innate disadvantages is unacceptable.

Timber and timber-frame
Timber construction, which is very common for domestic building worldwide, makes good ecological sense. Wood is a renewable resource and has low embodied energy; timber-frame structures are lightweight , easy to insulate to a high degree of effectiveness and can be readily converted, altered, added on to and remodelled. For builders, timber-frame construction is also both cost-and labour-effective. And because timber construction is relatively lightweight, foundations can be minimal, hence some post-and-beam timber-frame structures rest quite simply on individual concrete pads,rather than on slabs, which means less disruption to the site.
Although timber-frame construction, disguised behind masonary or brick cladding, is very common in housing developements, all-timber  construction is much more the exception in Britain and northern Europe today, because of the perceived risk of fire and the propensity of timber to rot when exposed to moisture. In some areas, timber structures is only permitted for structures of one or two storeys.Over the last 30 years (in Britain) timber has been exhaustively tested for its fire performance than any other material. Such studies have revealed that in the sizes used in construction , timber is slow to ignite,and once ignited burns very slowly. Treated with borax, a naturally occuring salt, timber meets British building regulations for fire-resistance and spread of flame.
 Green oak is the best timber for construction and is also affordable. Whitewoods and redwoods should be avoided if possible. Parts of the structure that might be more at risk from fire or vermin attack can be treated locally with borax paste squeezed into drill holes. Borax can also be applied externally provided it is subsequently stained over. An eco choice for external timber treatent is a non-toxic organic wood stain.
Because of their relatively low thermal mass, timber buildings do not store heat very well but can heat up quickly, while buildings with high thermal mass, which heat up slowly and lose heat slowly, require more energy to reach the desired level of warmth. But the low thermal mass of the timber building need not necessarily be a disadvantage. Such a building can be an ideal solution for modern working families: the heating can be left off during the day when family members are out at work and switched on in the evening to more or less immediate effort.
 Timber also has a role to play in hybrid types of construction. Good energy efficiency can be achieved when the basic structure is a lightweight timber frame, external walls are well-insulated timber and internal walls are made of high-mass materials such as concrete block or brick.

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