Some timber species are more effective at resisting fungi and termites than other species. This natural resistance or durability depends on the extractives the tree stores in its heartwood. Please note that durability is not determined by the density or ‘hardness’ of the species.

Durability Classes
Class 1 – highly durable
Grey Ironbark
Tallowwood
Cypress
Turpentine
Forest red gum
Grey gum

Class 2 – durable
Spotted gum
Blackbutt
Western red cedar
River red gum
Jarrah
Sydney blue gum
Stringy bark (yellow and white)

Class 3 – moderately durable
Brush box
Rose/flooded gum
Keruing
Messmate
Karri
Silver topped stringy bark

Class 4 – non-durable
Non- durable
Douglas fir
Hoop pine
Slash pine
Radiata pine
Mountain ash / Tasmanian oak
Meranti
Unidentified timbers
Sapwood of any species

The durability class only applies to the heartwood of the species. All untreated sapwood is considered non-durable. Core wood (wood from the very center of the tree) generally also has marginally lower natural durability than the rest of the heartwood as it was laid down when the tree was immature and production of the full range of extractives was not fully developed.
Measured by “graveyard tests” by examining the progressive decay of small wooden stakes buried in the ground, i.e. in-ground situation in an adverse environment - High moisture content, high temperatures and presence of termites.


We neglected maintenance for the relative natural durability. Please note that it is possible for even a Class 1 timber to degrade in service within 25 years if it is intermittently in contact with water. However, it fully protected, all durability classes can be more than 50 years.

Heartwood service life in years if exposed above ground:
class 1, 50+
class 1, 30
class 1, 15
class 1, 5 – 8