Timber Durability

Timber durability is a measurement of how long certain species of timber would last if a 50mm x 50mm cross section was left in the ground unprotected.

An untreated oak beam, which is classed as ‘durable’ will last 15-25 years depending on environmental conditions.

The following scale of durability was outlined by TRADA, the Timber Research And Development Association.

Durability	Class Designation	Average timber service life	Example Timber
5	Not durable	less than 5 years	American Ash
4	Slightly durable	5-10 years	American Popular Tulipwood
3	Moderately durable	10-15 years	American White Oak
2	Durable	15-25 years	–
1	Very durable	more than 25 years	–