Timber Truths: Why So Many Timber Playgrounds Fail

Across Australia, councils and asset owners are increasingly cautious about specifying timber playgrounds due to concerns around splitting, peeling, deterioration and maintenance. But while timber failures certainly exist, the industry often treats all timber systems as though they perform equally.

The reality is that timber performance varies enormously depending on what is actually supplied, and that, in turn, depends on what was specified. Too often, specifications rely on familiar terminology that sounds robust but leaves critical questions unanswered.

One of the most commonly used and frequently misunderstood terms in the recreation industry is ‘Class 1 Hardwood’. On its own, the term sounds reassuring. However, a durability classification (i.e. Class 1) describes only one aspect of timber performance. It is not, by itself, a complete specification.

Further, the term ‘Hardwood’ simply describes the botanical category of tree that a specific timber comes from. It says nothing about how durable that timber will be in an exposed outdoor environment. Some hardwoods perform exceptionally outdoors, while others do not. The category alone tells you very little about a timber’s suitability for a playground
application.

The difference between a timber asset that delivers decades of service and one that deteriorates prematurely can come down to just a few words in the specification.

So how can you be confident that the timber play equipment you are specifying will deliver the service life you expect? The answer starts inside the timber itself.

Understanding Timber Structure

Although timber is often discussed as though it is a single material, not all parts perform the same way. As a tree grows, it develops distinct layers, each serving a different biological function. From the outside in, these are the bark, sapwood and heartwood.

The bark forms the tree’s protective outer layer. Beneath it sits the sapwood — the living outer band responsible for transporting water and nutrients from the roots to the canopy.

As the tree matures, older sapwood cells gradually cease this transport function and become
heartwood. During this natural process, the timber accumulates naturally occurring extractives that significantly improve its resistance to fungal decay, termite attack and other forms of biological deterioration.

Although both originate from the same tree, heartwood and sapwood perform very differently
when exposed to the demanding conditions of Australian public play environments.

This distinction is fundamental because the durability characteristics commonly associated
with timber species relate only to the heartwood. But how is that durability actually measured?

Natural Durability Classifications

Natural durability classifications provide a valuable framework for comparing timber species. However, they are also one of the most misunderstood aspects of timber specification.

In Australia, the natural durability of timber is classified in accordance with AS 5604:2022 Timber – Natural durability ratings. The Standard classifies the heartwood of timber species according to their natural resistance to biological deterioration, including fungal decay and insect attack.¹

Natural durability ratings range from Class 1, representing the highest level of natural durability, through to Class 4, representing the lowest. In Australia, these ratings also provide an indication of expected life both in and above ground.

Adapted from Australian Standard 5604 (2022). Timber — natural durability ratings. Standards Australia, Sydney.

The important point to note is that these classifications apply to the heartwood only. They do not apply to sapwood, which does not possess the same natural durability characteristics. In fact, the Standard expressly states that untreated sapwood of all species is regarded as non-durable (i.e. Class 4), regardless of its classification.¹

This principle is further recognised throughout Australian guidance, including Timber Queensland Technical Data Sheet 25 (TQ TDS-25), which notes that natural durability ratings apply to heartwood and should not be assumed for sapwood.²

For specifiers, this distinction is critical. A durability classification describes the natural properties of the timber’s heartwood. It does not, on its own, describe the composition of the finished product or how it has been manufactured.

What This Means for Specification

A supplier can truthfully market a product as ‘Class 1 Hardwood’ while retaining significant sapwood. However, the presence of retained sapwood means the finished product cannot be expected to perform in the same way as one manufactured entirely from the durable heartwood on which the Class 1 rating is based.

Why does this matter?

Because sapwood absorbs moisture more readily, it is more vulnerable to biological attack and is significantly more prone to deterioration. Over time, retained sapwood can accelerate asset deterioration, affecting appearance, longevity and maintenance requirements. As deterioration progresses, it can also create safety risks that require remediation or replacement.

The ground line is where deterioration becomes a safety issue fastest. But sapwood will fail
wherever it is exposed to the Australian climate. It’s why even timber on mounted stirrups fails, and in fact, becomes a greater risk for structural failure.

Surely all suppliers remove sapwood?

Unfortunately, this is not the case. Sapwood removal is expensive and time-consuming. It is a manual, labour-intensive process requiring specialist craftsmanship. Unlike milled timber — where the machining process removes sapwood as a byproduct — round log playground posts must be stripped by hand, a process that demands skill and care to retain the natural organic form that makes the aesthetic valuable in the first place.

There is also a material cost. Removing sapwood means losing diameter. A significantly larger log must be sourced to achieve the same finished post size — and larger logs cost more. Suppliers working with smaller-diameter material, or buying in bulk without individual selection, simply cannot remove sapwood and remain price competitive.

The result is a market where the majority of timber playground products retain sapwood simply because removing it is harder and more expensive. That cost saving is passed on at purchase, resulting in what appears on the surface to be better value for money — but a product that is not fit for purpose in Australian public play environments where long-term durability, safety and asset performance are critical. An early cost saving ends up transferred to the asset owner in the form of increased maintenance, premature remediation and early replacement — costs that dwarf the original saving many times over.

Specification Implications

If your design intent is to achieve long-term performance associated with Class 1 Australian
hardwood, equipment specification should explicitly require sapwood to be removed.

Rather than specifying: Class 1 Hardwood

Consider specifying: Class 1 Australian Hardwood with sapwood fully removed.

This provides greater certainty that the finished product reflects the durability characteristics on which the Class 1 rating is based.

Key Takeaways

• Hardwood simply describes a botanical category of trees. It does not indicate durability for outdoor application.
• A Class 1 durability rating is not the same as a Class 1 finished product.
• Natural durability ratings apply to heartwood only; they do not apply to sapwood.
• A product marketed as ‘Class 1 Hardwood’ may still contain non-durable sapwood.
• Long-term timber performance depends on the complete specification, not the durability rating alone.

Read the full white paper

This article is an excerpt from Specifying with Confidence: Rethinking Timber in Public Play, an educational white paper exploring the considerations, challenges and opportunities of specifying timber in public play spaces. Discover practical insights and expert guidance to help inform material selection, design decisions and long-term performance.

Download the full white paper via the link below to explore the complete guide.

References

1. Australian Standard 5604 (2022). Timber — natural durability ratings. Standards Australia, Sydney.
2. Timber Queensland (2014). Technical Data Sheet 25: Outdoor Timber Performance. Timber Queensland, Brisbane.

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