Bowens - The Builders Choice

What You Need to Know About Treated Pine Sleepers

Building Advice
Jeff Harvey

Recently while holidaying in Queensland, I was little surprised to see Treated Pine Sleepers used in many situations. Thankfully in non-critical situations.

Why did I mention noncritical? Because the product should never be used in structural circumstances, particularly if it has been designed for structural retaining walls.

The regulation indicates that if a retaining wall is 1 metre or higher, it should be designed by a structural engineer and requires a building permit. The structural engineer should also specify a strength stress rating for the wood product that is selected. Also, they will generally specify hot dipped galvanized iron channel posts and depending on the job, at no more than 1.5 to 2 meter intervals.

Now to explain why the standard H4 200×75 treated pine product is not suitable for structural retaining walls.

“Now to explain why the standard H4 200×75 treated pine product is not suitable for structural retaining walls.”

Pine producers have always had trouble obtaining a reasonable return for the fast-growing middle of the pine log. This is because the fast-growing immature center lacks structural integrity. This wood also generally contains a large amount of non-treatable heartwood.

Summarising the above:

  • The 200×75 section is too fast-growing, lacks structural integrity and cannot achieve a structural stress rating
  • Being unseasoned, it is often not stable and can twist
  • Because it generally contains a significant amount of heartwood, the cell structure is clogged with substances that subsequently will not allow treatment penetration. For this reason, care needs to be taken when using H4 treated Sleepers for in general in-ground use. It would not matter if the treatment level was higher than H4 the heartwood cells still would not allow penetration.

We at Bowens are not saying the product should not be used, but only in appropriate situations. Accordingly, the product is described on our delivery dockets/invoices as a “Garden Grade Non-Structural” product.

Suggested uses are:

  • Non-structural retaining walls, below 1 meter
  • Garden surrounds
  • The product we sell is a non-arsenic treatment and can be legally used in public situations such as schools and playgrounds
  • Like all treated pine products, all cuts should have an end seal coating applied.

Furthermore, one can easily identify the treatment penetration difference by viewing the end grain; the heartwood is a light green shade and the treatable sapwood a deep green indicating penetration of treatment.

As always, we recommend referring to the installation guidelines for reference.

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