Durability wooden buildings: natural duration, actual duration, lasting foundations and some examples
Despite the recent and encouraging the rediscovery of the quality of wood by many designers, in Italy the term "wood in building construction" (speak "wooden architecture" is misleading and overly optimistic) means roofs (at best), railings for balconies, porches or sheds for agricultural use. All right, someone will say, there are also those beautiful polished floors where you can mirror yourself and those coatings that cost a fortune but they do so trendy ... but here the story ends. This is due to a whole range of cultural reserves, or rather, ancient prejudices and unjustified fears that lead to distrust what actually is the material, even the material par excellence. Few people know this, but the Latin word originally meant material fact "timber", and it is not a coincidence that even today wood is translated in Portuguese and Spanish term madeira madeira.
One of the main prejudices that weigh on wood construction concerns the durability (understood as the ability to maintain their resistance over time), as it was deemed precarious and highly perishable over time, despite this belief is unfounded. But believe it or not, know that it is easier to break an atom than a prejudice (Einstein). I, however, regardless of his warning, I intend to try the same.
First of all, the durability is not a trivial concept as it would seem, and this is why you have two different types: the natural durability and durability actual
THE DURABILITY 'NATURAL
The natural durability of wood is that factor that depends fundamentally on its essence (hardwoods are more durable than the sweet ones), and also varies in relation to the cut in question: it is usually higher in the heartwood (innermost layer, dense and compact than in mature trees makes up most of the volume of the stem) than sapwood (the outermost, newly formed and rich in reserve substances - mainly starch - therefore more easily attacked by wood-boring organisms). The greater resistance to biodegradation of the heartwood is mainly attributed to some extractives (organic compounds such as phenol type. Tannins), and it is always useful to remember that this durability, being the Nature never entirely predictable, may also vary within of the same species.
THE DURABILITY 'EFFECTIVE
The actual durability of a product depends not only on the natural durability of its materials, in this case the type of wood, but also on the climatic zone, from its class of use, and especially by the design and installation in a workmanlike manner that must be such as to prevent deleterious phenomena and dangerous such as the condensate.
The wood does not rot because of moisture in fact, but for condensation: it is therefore important to the laying of breathable materials that allow the passage of water, thus avoiding the risk of proliferation of pathogens such as fungi and molds. A classic example is that of the houses in prefabricated panels, where all these technical problems are already solved in the design phase, resulting in installation much easier.
EXAMPLES OF DURABILITY 'WOOD
The fact is that in most cases, contrary to widespread prejudice, wood is an extremely durable material. Some examples? Furniture with inlays of great artistic value found in the tombs of the Pharaohs were perfectly preserved for over 4000 years, and still today Japan boasts admirable architectural wood perfectly intact after 1,300 years of service. In the climate even more severe and rigid in Norway, there are many examples of beautiful churches entirely of wood (Stavkirker) built about 800 years ago by the best carpenters who ever lived, the Vikings, and have survived to this day.
We should not forget even the homegrown mountain huts centuries old and still inhabited, or even the old buildings with wooden framework, generally in oak, pine or larch, found mainly in Northern Europe and North America, as well as an entire neighborhood in the port Bergen (Norway), whose houses, built entirely in wood, are three age-old and still in excellent condition.
THE DURABILITY 'FOUNDATIONS OF WOOD
A further example is that of the foundation piles. Before the concrete foundations were made of timber and many valuable buildings are still supported on wooden poles, both in dry and wet, see about most of the historic houses in Venice or St. Isaac's Cathedral in St. Petersburg, or even two of the most impressive buildings in Amsterdam, Central Station and the Royal Palace, which still rests respectively 9,000 and 13,659 wooden pilings.
Nowadays many works of consolidation of landslide risk areas, escarpments and other soils erosion and steep slope are equally appeal to wood and its durability in the delicate work of bioengineering.
The quality of a manufactured article, especially in architecture, is also measured in relation to the number of problems that its maintenance in time involves, and that of a wooden building is among the less problematic in absolute, for example, is extremely difficult and inconvenient replace affected parts of structures in reinforced concrete or steel, wood vice versa allows considerable flexibility, extending the life of the building. Suffice it to say that the warranty issued by the manufacturer of a building prefabricated wood is on average 30 years compared to 10 years in a building of traditional masonry. The durability of wood products is even greater when you consider the possibility that now offer some modern wooden buildings necessary to be dismantled and rebuilt elsewhere with the same materials, reusing / recovering any waste. This possibility simply does not exist or would be economically and physically impractical for conventional masonry buildings and structures in steel or reinforced concrete.
Sources |
Jordan G. Wood Technology - Vol 1., The raw material, UTET, Turin, 1981
Dulbecco P., D. Luro, L'essentiel sur le bois. CTBA, Paris, 1998
Berti S., Piazza M., R. Zanuttini, Timber structures for sustainable construction. Raw materials and products. Design and implementation. Series: Manuals building. Tools for designers and contractors, Il Sole 24 Ore, 2002
20/03/2012
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Translated via software
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Source:
Italian version of ReteIngegneri.it