Healthy Environment, Healthy Community, Healthy Business

Environment Protection Authority

Environmental Issues

Chemicals and pesticides

Timber treatments

If possible, choose an arsenic-free alternative.

blue pine and yellow laminated veneer lumber

House frame built with blue pine and yellow LVL beams.

Many factors affect how well timber treatments work, including:

  • what chemical or mixture of chemicals is used
  • the concentration of chemicals
  • which part of the timber is being treated
  • how the treatment is applied
  • how long the chemicals stay in the wood

The harsher the environment, the deeper, longer lasting and stronger the treatment needs to be.

To choose the best treatment for the job take into account location, the type of pests and fungi the timber will be exposed to, and the purpose of the final product.

Hazard levels

In Australia six main hazard (H) levels help you choose the most appropriate treated timber for the job. The levels are determined by the environment the timber is to be placed in (interior, exterior, above ground, in ground, in fresh water or in salt water), the types of pests the timber is exposed to and its intended use. Hazard levels are defined by Australian Standard 1604.1.

The H levels are also determined by chemical type and strength, penetration depths and retention rates. See the Hazard levels and chemical treatment types chart for more information. 


Preservatives are applied to timber in a number of ways, including dipping and spraying, or as an additive to glue for laminated veneer lumber (LVL) products.

They can also be forced into the timber via vacuum pressure impregnation (VPI). To do this a ‘charge’ (stack) of timber is placed inside an air-proof cylinder. A vacuum is then applied to remove as much water as possible. Treatment chemicals are then pumped in under pressure until the nominated uptake is achieved. A final vacuum extracts any remaining preservative.

Page last updated: 12 May 2016