Timber Treatment in Australia and What it is Used For

Posted by Daryl Schmidt on 21st Feb 2022

TIMBER TREATMENT LEVELS

From the Timber Preservation Association Australia - http://www.tpaa.com.au/

According to Australian Standard AS/NZS1604 parts 1 to 5, any product claiming to be preservative treated must be branded as specified in the standard. An important part of the brand is the Hazard Class, which indicates the service conditions to which the product is exposed and the level of treatment or level of protection that must be applied to the wood.

The Hazard Classes have been defined as follows:

Hazard Class	Exposure	Service condition	Hazard	Example uses
H1	Inside above ground	Completely protected from the weather, well ventilated and protected from termites	Borers	Susceptible framing, flooring, furniture, interior joinery used across Australia
H1.2 **	Inside above ground	Completely protected from the weather, but with possible exposure to moisture	Borers and decay	Wall framing
H2	Inside above ground	Protected from wetting, no leaching.	Borers and termites	Framing, flooring, furniture, interior joinery used across Australia
H2F	Inside above ground	Protected from wetting, no leaching.	Borers and termites	(Envelope treated) framing used south of the Tropic of Capricorn
H2S	Inside above ground	Protected from wetting, no leaching.	Borers and termites	Framing used South of the Tropic of Capricorn
H3	Outside above ground	Periodic moderate wetting and leaching	Moderate decay, borers and termites	Weatherboards, fascias, pergolas, framing etc.
H3A ##	Outside above ground	Periodic moderate wetting and leaching	Moderate decay, borers and termites	Weatherboards, fascias, pergolas, framing etc. – under a regularly maintained paint coat system
H3.1 **	Outside above ground	Periodic moderate wetting and leaching	Moderate decay, borers	Weatherboards, fascias, pergolas, framing etc. – under a regularly maintained paint coat system
H3.2 **	Outside above ground	Periodic moderate wetting and leaching more critical end uses	Moderate decay, borers	All H3.1 uses plus structural and decking
H4	Outside inground	Severe wetting and leaching noncritical applications	Severe decay, borers and termites	Fence posts, retaining wall less than 1 m high, landscaping timbers.
H5	Outside inground with or in fresh water	Extreme wetting and leaching, critical application	Very severe decay, borers and termites	Piling, house stumps, power poles cooling tower fill, building poles, retaining walls more than 1m high
H6	Marine waters	Prolonged immersion in sea water	Decay and marine wood borers	Boat hulls, marine piles, jetty cross bracing, jetty landing steps.

## Applies to one preservative system used in Australia **Applies in New Zealand only