Basic info is found in Chapter 10.
Timber has been the main structural material for the nomad's tent as well as the sedentary farmer's house in all corners of the world, especially for roof construction, where its lightweight and structural properties have made it more attractive than any alternative.
On the basis of relative weight, high quality timber is stronger than steel. The safety factors needed in the design of wood structures are, however, high. The average strength is ten times higher than the design strength. The reason for this over-engineering is the occasional irregularity in the wood that means that it may be weak in a few places. Good selection can reduce this.
Timber structures have usually been limited to small buildings because of the fire risk; although there are many developments in the use of timber in much larger buildings. The reasons for this are the improved possibilities for technical fire protection and the revised view of timber's own properties in relation to fire, which are better than previously thought. In timber of a certain size, the outer layer chars and then effectively stops further burning of the inner core of the timber.
Building in timber entails much lower environmental pollution and energy use than construction systems in steel, concrete or brick. Substituting these materials with timber would considerably reduce the overall environmental impact of the construction sector. To this can be added timber's function as a carbon sink. As timber grows, every kilogram of wood binds between 1.5 and 1.8 kilograms of carbon dioxide from the atmosphere. This will remain 'stored' until the building is burned or decays. It is thus desirable to maximize use of timber especially in the most long-lasting parts of buildings, such as the structural system.
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