What is Class 1 Timber Durability?

Class 1- Timber of the highest natural durability, expected to have a life greater than 25 years in the ground and greater than 40 years exposed above ground.

Class 2 – Timber of high natural durability, expected to have a life of about 15 to 25 years in the ground and 15 to 40 years exposed above ground.

Class 3 – Timber of moderate natural durability, expected to have a life of about 5 to 15 years in the ground and 7 to 15 years exposed above ground.

We don’t recommend using timber above class 2 for exterior use.

Source: https://www.woodsolutions.com.au/glossary/Durability-Class