Timber Durability Ratings: How They Work and What They Mean

At Narangba Timbers, if you are buying timber for decking, flooring, fencing or structural elements, we always recommend the timber that is going to give you the best performance. We want it to be durable, strong and attractive enough that you will love it for the next fifty years. In other words, we put timber selection on autopilot for you.

However, a lot of our customers like having every scrap of information on their building materials. We are always happy to comply and provide as much information as you need to make a decision with which you are going to be comfortable, both now and after the project is completed.

Timber Decking in Brisbane

Timber Decking Lifespan

The lifespan of any timber project is determined by the durability of the timber, the hazard level and what the material is being used for.

An extremely durable piece of timber being exposed to no hazards that is never asked to bear weight, for example, is going to last longer than a piece of timber that has lower durability ratings exposed to more hazards and extensive weight bearing.

Once again, we always like to use strong, durable timber and try to protect it from hazards as much as possible.

Hazard Levels and Applications

H levels represent the level or degree of biological hazard that timber will be exposed to in a specified application.

The low end of hazard level ratings is H1. The high end is H6 or H6SW.

H1 Timber

H1 is for indoor use, above ground in a fully-protected and well-ventilated area.

H1 timber offers protection against borers.

H2 Timber

H2 is also intended for indoor use above ground, in an area protected from leaching and wetting.

H2 timber offers protection against borers and termites.

H3 Timber

H3 timber can be used outside above the ground in an area that allows moderate wetting and leaching.

It offers protection against decay borers and termites.

H4 Timber

H4 timber is designed for use outside and in the ground where there is severe wetting and leaching.

It offers protection against termites, borers and severe decay.

H5 Timber

H5 timber can be used with full contact to the ground. It can be exposed to extreme wetting, leaching or critical use.

It protects against borers, termites and very severe decay.

H6 Timber

H6 timber is for marine use. It can be submerged in saltwater.

It protects against marine wood borers and decay. H6SW is for marine use in Sth waters only.

It also protects against marine wood borers and decay.

Timber Durability Ratings

The durability rating of a species (displayed as a Class) of timber relates to the natural ability of the heartwood of that species to resist decay and insect pests.

Class 1 Timber Durability

Class 1 is the highest durability rating.

Class 1 means that timber is projected to last for 50+ years in a fully protected area and 50+ years outside above the ground.

Class 1 timber lasts for 25+ years if it is in the ground, such as a deck pole.

Class 2 Timber Durability

Class 2 timber also lasts for 50+ years inside and fully protected.

When it is used outside above the ground, its life expectancy is 30+ years.

When it is in the ground, its projected usage is 15-25 years.

Class 3 Timber Durability

Class 3 timber lasts 50 years fully protected, 15 years above the ground and 8-15 years in the ground.

Class 4 Timber Durability

Class 3 timber lasts 50 years fully protected, 5 to 8 years above the ground and less than 5 years in the ground.

Treated Timber

Timber can be treated with CCA, Boron, ACQ, LOSP or CCA and Creosote.

At Narangba Timbers we stock CCA treated timber because it is good for all hazard levels.

CCA, or Chromated Copper Arsenate, is toxic and for recommended applications only.

It can’t be used in situations where people will come in contact with it regularly, especially children.

Burning it to dispose of it is dangerous and releases dangerous toxins into the air.

What it All Means to You

As we stated earlier, we like to put it on autopilot for you by carrying only the best timber.

Most of our timber is Class 1 hardness and the few that are Class 2 are still very durable.

Most of the timber for decking or fencing is going to be rated at H3 or H4, which is perfect for either.

If you are ready to get your project started or you just need some more information, feel free to call us today: (07) 3888 1293.

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Posted in Jack's Blog, Timber Decking Brisbane