The durability of timber

All timber breaks down eventually (Table 10.9). This can happen either through oxidization or through reaction with micro-organisms. These processes of deterioration usually work together. Timber that is submerged in water is more durable because of the lower availability of oxygen; in swamps, timber can lie for thousands of years

Table 10.9 Durability of timber

Species

Always dry (years)

Sheltered outside (years)

Unsheltered outside (years)

In contact with earth (years)

Underwater (years)

Ash

300-800

30-100

15-60

Less than 5

Less than 20

Aspen

-

Low

-

Low

High

Beech

300-800

5-100

10-60

5

More than 300

Birch

500

3-40

3-40

Less than 5

20

Elm

1500

80-180

6-100

5-10

More than 500

Juniper

-

More than 100

100

-

-

Larch

1800

90-150

40-90

9-10

More than 1500

Maple

-

-

-

Less than 5

Less than 20

Oak

300-800

100-200

50-120

15-20

More than 500

Pine

120-1000

90-120

40-85

7-8

500

Poplar

500

3-40

3-40

Less than 5

-

Spruce

120-900

50-75

40-70

3-4

50-100

Willow

600

5-40

5-30

-

-

without deteriorating. Timber seems to be resistant to aggressive air pollution-as evidence of such damage occurring in timber has never been found.

Timber thus endures 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 607 AD. There are also completely intact timber beams in the 2000-year-old ruins of Pompeii. Norwegian stave churches are up to 900-years-old.

However, some factors are now beginning to threaten timber's reputation. The extensive use of artificial fertilizers is probably reducing its durability, since the fast growth of cells produces a spongier, more porous timber. Fast-growing species were introduced in the 1950s and have proven to yield lower quality timber. These conditions also led to a greater need to impregnate timber with chemicals, see Chapter 19.

Was this article helpful?

0 0

Post a comment