Timber Hazard Levels

 In Timber Education Blog

When purchasing timber there are a few things to take into consideration, hazard levels and treatment type. Hazard levels are indicators for appropriate use of treated timber. The degree of what timber is exposed to is known as the “hazard”. There are appropriate treatments defined for each hazard class. Timber treatments are used to prevent deterioration by insect, fungal attacks and to preserve the quality of timber.

Hazard class can also depend on other factors such as temperature, moisture prevailing in the location of exposure environment. The higher hazard class number is indicative of a more severe hazard.

Hazard levels:

Untreated Timber

This timber is used where there is no risk of dampness. It is used in production, delivery and storage applications where there is low risk of exposure to external or internal moisture conditions. An example of untreated timber in use is our Kids Kitsets.

Untreated timber is high temperature kiln-dried untreated radiata pine.

H1 Hazard Level

H1 timber is when timber is protected from weather above ground. This is the minimum level of preservative treatment required to protect timber from these circumstances and attack by insects, including termites. This hazard level is suitable for in above-ground well ventilated applications protected from weather and wetting.

H3 Hazard Level

H3 pine is treated to resist moderate decay, borers and termites. It is suitable for outside above ground use. Depending on the application, H3 preservative treatment can involve two different levels (H3.1 and H3.2).

H3.1 Hazard Level

H3.1 timber is submerged into treatment and forms an envelope seal. This timber can be exposed to weather, but only in vertical (water-shredding applications) such as weatherboards where the water does not penetrate the timber. Cut ends must be resealed with paint-on timber preservative such as Metalex.

 H3.2 Hazard Level

H3.2 hazard level timber has been pressure treated inside a sealed chamber. Treatment penetrates the inside of the timber as well as protecting the outside. H3.2 Timber is used outdoors above ground where there is risk of water entrapment. For example, decking and fencing.

H4 Hazard Level

H4 timber is used for exterior in-ground or in direct contact with ground use. For example, landscaping applications, fence posts, pergola posts and garden walls. H4 timber is exposed to weather, in ground or in fresh water. It is appropriate for less critical “non-structural” applications.

H5 Hazard Level

H5 timber is used for critical major structural components in ground contact. Exposure of this timber is in contact with the ground or concrete. Items that use this hazard level are retaining wall poles, house piles and crib walling.

H6 Hazard Level

H6 timber is only used in marine applications where timber is either in contact with seawater or estuarine ground. It is suitable for critical major components built in these areas. For example, sea walls and wharf piles.





Hazard levels of timber used at MLC Group

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