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What is H4 Treated Pine? (Australian Guide)

H4-rated treated pine protects against severe decay as well as termites.

H4 treated pine is a type of wood that is not only durable and cost-effective, but can be used in many different applications.

Looking to use H4 treated pine in your next project?

This blog post covers everything you need to know.

What is H4 treated pine?

H codes represent different levels of timber preservative treatments. The different levels provide a different level of protection against biological decay.

The codes range from H1 to H6 with each code representing a different required minimum treatment.

H4 is one of the higher levels of treatment and H4 timber is suitable for a range of indoor and outdoor applications.

What are timber hazard levels?

A Hazard level classification determines what level of protection timber has against certain exposures.

These range from H1 – H6, as displayed in the table below.

Timber Hazard level table | Building & Landscaping Materials
This table showing timber hazard level and treatment types has been reproduced with permission of the NSW Environment Protection Authority.

According to QTimber, H4 timber is the “minimum level of preservative treatment required to protect the timber from attack by insects, including termites, and severe decay. H4 treatments are suitable for use in situations where the timber is in contact with the ground or is continually damp. H4 is appropriate for less critical ‘non-structural’ applications and/or where the decay hazard zone indicates a lower in-ground hazard.”

H4 treated pine is a type of timber that’s been chemically treated to withstand decay under severe weather conditions.

It’s moisture-resistant and also protected against insects, including termites.

Because H4 is suitable for outside, in-ground use, it can be used for fence posts, decking foundations, or other applications where the wood will contact the soil.

The table here displays where the H2 Hazard Class sits in the Hazard Class Selection Guide.

What is H4 pine used for?

Treated timber 2 | Building & Landscaping Materials

H4-rated treated pine is suitable for a wide variety of outdoor applications, including:

  • Decks and pergolas
  • Fence posts
  • Garden edging
  • Timber framing
  • Pergola posts
  • Landscaping and retaining walls

Source

What is the difference between H2 and H4 treated pine?

H2 treated pine is used for indoor projects and cannot get wet, whereas H4 treated pine can be used for outdoor projects, either above or in-ground.

H2 treated pine is less expensive than H4 but doesn’t offer as much protection against the elements. It protects against insects, including termites, but not against fungal decay (rot).

H4 treated pine protects against fungal decay because it’s designed to be installed outdoors or in direct contact with soil (like a retaining wall), where damp conditions are more likely.

Source

What is the difference between H3 and H4 treated pine?

H3 Treated Pine is treated against termites, borers and fungal decay. It is suitable for outside, above-ground use only.

H4 Treated Pine provides additional protection to H3, protecting against severe decay that can occur when timber is in contact with water, such as for your decking posts that are in contact with the ground.

Source

How long does H4 treated pine last in the ground?

The lifespan of H4-treated lumber depends on the type of timber and the conditions it’s exposed to.

As explained in this article, the estimated typical service life of H4 treated softwood ranges from 9 years to 60 years depending on the shape and diameter of the wood.

The most common factor that affects the longevity of pressure treated wood is moisture. The more exposure to wet soil, the shorter its life span will be. Protecting your posts from excess moisture can help them last longer.

Can you use H4 treated pine for garden beds?

Raised garden bed | Building & Landscaping Materials

H4 treated pine is suitable for garden beds where the soil may be damp.

This is because it’s designed to resist rot and termites when buried in the ground – as well as above ground.

CSIRO has said that the risk from using CCA treated timber for vegetable gardens is within tolerable limits.

However, for growing vegetables, some people prefer to not use any kind of treated timber.

Some people who used treated timber for vegetable gardens like to line it with plastic or paint the timber with an exterior grade paint.

If you’re building a garden for growing vegetables, the safest option is to use untreated hardwood sleepers like Kwila (Merbau) or Jarrah.

You could also consider using the newer ACQ-treated pine sleepers (which are arsenic-free).

Does Bunnings sell H4 treated pine?

Bunnings stocks a range of H4 treated pine.

Sizes include:

  • 200 x 50mm 1.2m
  • 200 x 50mm 1.8m
  • 200 x 50mm 2.4m
  • 200 x 50mm 3.0m
  • 200 x 50mm 3.6m

At the time of writing, prices for Bunnings H$ treated pine range from $9.40 to $28.40

FAQ

What sizes does H4 treated pine come in?

H4 treated pine timber comes in a range of sizes and is available from many building supplies and DIY stores including Bunnings, Mitre 10, and more. Many different lengths are typically stocked by suppliers but common sizes are 2.4m, 2.7m, 3.0m, and 3.6m. Most suppliers will also be able to offer custom cut lengths if you need a specific size or want to avoid waste from buying a full-length length and cutting it down yourself.

Photo of author

Steve Kropp

Based in Melbourne, Steve's passion is vegetable gardening, and he’s been writing about it for almost 5 years. He also loves all things DIY and is always looking for a new project. When not working on his own garden projects or blogging, Steve enjoys spending time with his family, cooking meals with produce harvested from his garden, and coaching his son’s footy team.

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