Treated timber for fencing projects

July 17, 2015

We are often asked what type of treated timber is required for a residential timber fence.

The most commonly purchased timbers for fencing projects are:

CCA H3 Pine Palings & Colonial Pine Palings
CCA H3 Pine Rails
CCA H4 Pine Posts
CCA H4 Hardwood Posts
CCA H4 Pine Sleepers
CCA H4 Hardwood Sleepers

So what do these “CCA” & “Hazard Class” Classifications mean?

The below guide assists in clarifying the Hazard Class & Suitable timbers for such projects:

Service Condition	Hazard Level	Possible Hazards Encountered	Appropriate Applications	Requirements for Hardwoods & Softwoods
Outside Above Ground	H3	Moderate decay conditions (rot), borers & termites.	Fence palings & rails, cladding, decking, fascias, pergola rafters, beams & battens, handrails & balustrades, posts not in ground.	Hardwoods of Above Ground Durability Class 1 or better with sapwood preservative treated to H3. (Small proportions of untreated sapwood may be permitted by some grading standards. Some Above Ground Durability Class 2 & 3 timbers are suitable in some locations for non-structural uses in these applications depending on climate, detailing & maintenance of the project coating. Softwoods preservative treated to H3 or better with untreated heartwood limited.
Outside In-Ground	H4	Severe decay conditions, borers & termites.	Non critical applications such as fence posts, landscaping, garden walls & pergola posts.	Hardwoods of In-ground Durability Class 2 or better with the sapwood limited or preservative treated to H4. Softwoods preservative treated to H4 or better with untreated heartwood limited.
In-Ground Contact or Fresh Water	H5	Very severe decay conditions, borers & termites.	Critical applications such as house piles & posts, structural retaining walls, deck posts, poles, decking close to or on the ground & similar.	Hardwoods of In-ground Durability Class 1 with the sapwood removed or preservative treated to H5. In-ground Class 2 rounds with a complete envelope of sapwood preservative treated To H5. Softwoods preservative treated to H5 or better with untreated heartwood limited.

For more information regarding “Natural Durability Class” & “Species Durability Ratings”

Timber Queensland - Outdoor Timber Performance

Resource: Timber Queensland

What is CCA Timber Treatment

CCA treated timber has been impregnated with Copper, Chromium and Arsenic salts.

CCA is impregnated into timber using a vacuum/pressure cycle & is designed to react with the wood cell components so that the active elements, copper (Cu), chromium (Cr) and arsenic (As) are fixed into the wood's structure.

These are chemical preservatives used to protect non-durable wood from rotting, fungal degrade, termites & other wood boring insects. The treatment is also resistant to leaching and therefore it can be used on timber that will be exposed to the elements or used in-ground.

Example of CCA H3 Treated Pine Palings.

Is it safe?

All treated timber manufactured by reputable companies & handled correctly is safe. CCA treated timber has been world-wide for more than 70 years without evidence of harm to human or environmental health.

Restrictions on sale of CCA preservative treated timber for some uses

Under an agreement that the timber industry has with the Australian Pesticides and Veterinary Chemical Authority (APVMA) timber treated with CCA before 7th June 2006 can continue to be sold for all applications.

The APVMA requires that after 7th June 2006, timber may not be treated with CCA preservative if it is to be used for certain uses and the timber industry has imposed voluntary restrictions on the sale of timber treated with CCA for certain uses.

Those uses are:

Children's play equipment
Garden furniture
Picnic tables
External seating
Domestic decking boards or
Handrails

In addition to these restrictions, CCA treated products must be individually and legibly marked with the words "Treated with copper chrome arsenate" to first point of use.

Example of Treatment labelling

Small CCA treated products don't have to be individually marked however the pack must be legibly marked with the words "Treated with copper chrome arsenate" to first point of use.

Small products are:

Fence palings, battens and droppers
Veneers
Timber with a cross section of 1500mm² and less (except light decking)
Timber less than 15mm thick (except light decking)
Timber less than 500mm long

Correct Timber Handling

Working with timber (treated or untreated) produces dust particles which can cause discomfort to skin, eyes & upper respiratory tracts. Therefore the protection of the hands, eyes, nose & mouth when sanding, sawing & planing is always highly recommended.

For more information refer to the following downloads:

Timber Queensland - Outdoor Timber Performance

Timber Queensland - Residential Timber Fences

Timbers Queensland - Recommendations for the use of Treated Pine Outdoors

Timbers Queensland - Timber Garden Walls (Retaining walls up to 1 Metre High)

Timber Queensland - Timber Retaining Walls for Residential Applications

5 Star Timbers - blog