Timber Durability Scale and Rating

Timber durability header

Durability is a measurement of how long specific 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', for example, 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 Siberian Larch
3 Moderateley Durable 10 - 15 Years Douglas Fir
2 Durable 15 - 25 Years European Oak
1 Very Durable More Than 25 Years Teak

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