Civil Engineering Reference
In-Depth Information
Figure 10.4: Principle for solar drying of timber. Source: Hall 1981
When building with logs it is best to fell, notch and use the timber while it is
still moist. Logs with large dimensions have a long drying time - it can take
years! A log building will therefore shrink between 5 and 10 cm on each floor.
When the moisture content has decreased to 15-20 per cent, windows and pan-
elling can be installed. Around 1900 this method of building fell out of favour
because it was labour intensive and slow. If a framework construction is built of
ready-dried timber, there is no noticeable shrinkage.
The durability of timber
All timber breaks down eventually. This can usually happen either through oxi-
dization caused by oxygen in the air, or through reaction with micro-organisms
which attack the proteins and therefore the sugars. These methods of deteriora-
tion usually work together. Timber that is submerged in water is more durable
because of the lower amount of oxygen; in swamps timber can lie for thousands
of years without deteriorating.
Timber keeps as long as it is not attacked by fire, insects or mould. The oldest-
known timber building in existence is the Horiuji temple in Japan, which was
built of cypress in AD 607. There are also completely intact timber beams in the
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