Non-durable timbers

Non-durable timbers have a low resistance to decay and insect attacks, and they are classified as such based on the performance of their heartwood in ground contact. The durability of most timbers varies widely, and even pieces cut from the same tree can show significant differences. Timbers have been classified into five broad grades based on the performance of their heartwood in ground contact, and non-durable timbers have an approximate life of 5-10 years in contact with the ground.

Examples of non-durable timbers:
 * Birch and Beech: These are considered Class 5, which means they are not durable and have a life span of 0-5 years.
 * Ramin: This is one of the least sustainable woods and has a low natural durability.

The durability assessment is only based on the tree's heartwood and not its sapwood, as only the heartwood, due to its extractives, has any appreciable degree of durability.