Civil Engineering Reference
In-Depth Information
Table 10.7: Durability of timber in years in different situations
Timber
Always dry
Sheltered
Unsheltered
In contact
Underwater
outside
outside
with earth
Pine
120-1000
90-120
40-85
7-8
500
Spruce
120-900
50-75
40-70
3-4
50-100
Larch
1800
90-150
40-90
9-10
More than 1500
Juniper
-
More than 100
100
-
-
Oak
300-800
100-200
50-120
15-20
More than 500
Aspen
-
Low
-
Low
High
Birch
500
3-40
3-40
Less than 5
20
Maple
-
-
-
Less than 5
Less than 20
Ash
300-800
30-100
15-60
Less than 5
Less than 20
Beech
300-800
5-100
10-60
5
More than 300
Elm
1500
80-180
6-100
5-10
More than 500
Silver fir
900
50
50
-
-
Willow
600
5-40
5-30
-
-
Poplar
500
3-40
3-40
Less than 5
-
1900-year-old ruins of Pompeii. An untreated timber surface can last for 150 years
under favourable conditions. As a rule of thumb, heavier timber will last longer.
Timber is very resistant to aggressive pollution in the atmosphere - evidence
of such damage occurring in timber has not been found.
Some factors are now beginning to threaten timber's good reputation. The
extensive use of artificial fertilizer is probably reducing its durability, as the fast
growth of cells produces wide annual rings and gives a spongier, more porous
timber. Fast-growing species were introduced in the 1950s which have proved to
yield lower quality timber. These conditions also led to a greater need to impreg-
nation timber with chemicals.
Recycling
Timber is a recyclable material, and in the form of prefabricated components it can
be re-used in many different situations. The re-use of logs, in part or as a whole,
has been ubiquitous in most of Norway and Sweden. Both log construction and
stave construction are building techniques where the components can be easily
dismantled and re-erected without any waste. The Japanese have developed a
whole series of techniques for timber joints without glue, the most well known
being the so-called 'timber locks'. Most structures in the twentieth century have
been based upon less flexible principles. Gluing and nailing have been the domi-
nant methods of jointing. Modern timber-frame construction is at best firewood
after demolition! Some chemicals, glues and surface treatments make timber
unsuitable for use as fuel, and it has to be considered a problematic waste.
 
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