How Timber Durability Ratings Work

All timber suppliers across Australia, are asked often about durability ratings for timber. Believe it or not, they may not be what you think they are. For example, if you wanted to know the durability of work shoes, you would probably want to know how they will stand up to physical stresses and how long they will last.

Timber durability ratings don’t work that way. While they do serve as a good estimate of how long timber will last in many applications, it isn’t the standard physical stresses that timber durability ratings cover. The durability rating of timber is a measurement of how long it will stand up to fungi and insects such as termites or lyctid borers that attack hardwood.

In addition, sapwood of any species provides almost no resistance, so durability ratings only apply to the heartwood of all hardwood species. The ratings are determined by testing and by the experience of experts in the field. For testing, poles and stakes of various timber species are driven into the ground and monitored.

While timber ratings do have numbers assigned to them, they can’t actually predict how long any species will last in any particular application because there are so many variables. Timber durability or lifespan can be affected by a number of factors, including moisture, temperature, weather, use and whether or not the labour was competent.

There are four durability classes. Class 1 is the highest rating or the longest expected lifespan. Class 4 is the lowest rating. All classes of hardwood are expected to survive more than 50 years when fully protected from the elements, meaning they are indoors and there is no termite infestation. Here is a quick table for the durability ratings for timber that is outdoors above ground and timber that is in the ground.

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To learn more or to place an order, call Narangba Timbers today on 1300 477 024.