Timber Durability Classifications

 

Timber durability refers to a species of heartwood natural resistance. Most timbers will last over 50 years if they are indoors and protected from insect attacks and moisture.

 

It is essential to know the timber classification if the timber will be used outdoors, as timber durability varies a lot from one species to the other.

 

There are two types of outdoor usage, in-ground and above-ground. One species is common to have a different classification between the two uses. For example, white cypress has class 1 durability above ground and class 2 in-ground.

 

Timber species have been classified into four different durability classifications.

 

Class 1: Species that make this classification will last at least 25 years in-ground and over 40 years above ground. Here are the most popular timber species of this classification, Tallowwood, Grey & Red Ironbark, White Mahogany and Forest Redgum.

 

Class 2: Species that make this classification will last up to 20 years in-ground and 40 years above ground. Here are the most popular timber species of this classification, Red Mahogany, River Red Gum, Blackbutt, Spotted Gum, White Cypress, Jarrah and Turpentine

 

Class 3: Species that make this classification will last up to 15 years in-ground and up to 15 years above ground. Here are the most popular timber species of this classification, Red, Yellow, White & Brown Stringybark, Southern Mahogany, Sydney Blue Gum, Silvertop Ash, Kwila (Merbau), Karri, Western Red Cedar, Mountain Grey Gum and Messmate

 

Class 4: Species that make this classification will last up to 5 years in-ground and up to 7 years above ground. Here are the most popular timber species of this classification, Mountain Ash, Douglas Fir (Oregon), Myrtle Beech and untreated Radiata Pine.