TL;DR
- The Australian Standard AS/NZS 1604 defines six hazard classes (H1–H6), each suited to specific levels of exposure and moisture.
- H2 timber is designed for dry, indoor framing, while H3 is treated for outdoor, above-ground applications.
- H3-treated pine is commonly used for cladding, handrails and screening because it resists fungal decay, insect attack, and weather exposure.
- H4 timber is required for in-ground or constant moisture contact to prevent rot and maintain structural integrity.
- Always match the treated timber hazard class to the intended use and environment to comply with Australian Standards and avoid costly mistakes.
Timber is one of the most versatile natural building materials – renewable, strong, and suitable for a broad range of construction applications. But not all timber is created equally. Its performance depends on its timber hazard class, which determines the level of risk posed by biological hazards such as fungal decay and insect attack.
When building homes, decks, or pergolas, it’s vital to choose the right treatment class for your intended use. Whether you’re sourcing treated pine for residential construction or commercial and industrial projects, understanding the treatment process helps ensure structural integrity and compliance with Australian Standards.
What Are Timber Hazard Classes?
A timber hazard class indicates how effectively treated timber products can resist wood-destroying fungi and insects, such as borers and termites. Each class represents a specific treatment required for a given environment – from indoor framing to in-ground exposure.
Following the correct treatment process ensures compliance, long-term durability, and protection for your outdoor applications. Using the wrong class can compromise structural integrity, leading to costly repairs.
Timber Hazard Class Overview
| Hazard Class | Typical Exposure | Common Applications |
| H1 | Indoors, completely protected from moisture | Furniture, flooring battens |
| H2 | Indoors, termite-prone regions | Framing and trusses |
| H3 | Outside, above ground, exposed to weather | Cladding, treated pine decking, pergolas |
| H4 | In ground or fresh water | Fence posts, garden sleepers |
| H5 | High moisture or heavy ground contact | Retaining walls, structural posts |
| H6 | Marine and saltwater contact | Jetties, wharf piles |
Selecting the correct hazard class ensures your timber products are suitable for their intended use and that you avoid costly mistakes during construction.
H2 vs H3 Timber – Understanding the Difference
The main difference between H2 vs H3 timber lies in moisture exposure and environment.
- H2 timber is intended for indoor use in well-ventilated areas, protected from rain. It’s ideal for framing in residential construction, where only termites pose a risk.
- H3 timber is for outdoor use, where timber faces periodic wetting but remains above ground. It’s commonly used in outdoor projects like pergolas and decks.
H3-treated pine undergoes a deeper treatment process. Builders should always match treated timber ratings to exposure levels to ensure durability and long-lasting performance.
What Is H3 Treated Pine Used For?
If you’re wondering ‘what is H3-treated pine used for?’ – it’s one of the most popular choices for outdoor structures where timber remains above ground.
Common outdoor applications include:
- Decking boards
- Pergolas, fences, and exterior beams
- Fascia boards, verandah posts, and cladding
Always ensure you’re buying from trusted building supplies to guarantee proper treatment and compliance.
H3 vs H4 Timber – Choosing the Right Level for Outdoor Applications
When comparing H3 vs. H4 timber, the distinction comes down to exposure level and contact with ground or fresh water.
- H3-treated pine is ideal for outdoor use above ground, like decks, pergolas, and cladding. It provides strong resistance to fungal decay where timber is exposed to periodic wetting and drying.
- H4 timber is required for in-ground applications where timber is in constant contact with concrete or soil – such as fence posts, and sleeper retaining walls.
Using H3-treated timber where H4 is required can cause early decay and loss of structural integrity. For outdoor projects, this distinction is critical to avoid costly mistakes.
Tip for builders: Always check the Australian Standards or supplier guidelines before choosing a treated timber grade. The right treatment class ensures durability and compliance for your construction project.
How to Choose the Right Hazard Level for Your Project
Selecting the correct treated timber starts with assessing your environment and intended use.
- Exposure: Determine if timber will be above ground or in-ground, exposed to periodic wetting, or in contact with fresh water.
- Application: Consider whether you’re building decks, framing, or retaining walls.
According to the Timber Preservers Association of Australia, “Selecting the appropriate hazard class ensures the right treatment required for the environment, preventing early decay and maintaining compliance with Australian Standards.”
Consult your timber supplier before purchase to confirm treatment specifications and ensure you get the right treated pine for your project.
Maintenance Tips for Treated Timber
Even high-quality treated timber benefits from maintenance. Follow these steps to extend its life:
- Seal cut ends after installation to preserve treatment integrity.
- Keep outdoor structures like decks and pergolas clear of soil to limit moisture buildup.
- Re-coat a paint or transparent timber finish every few years for added protection.
- Store unused pine timber in a well-ventilated area to prevent warping.
Ongoing maintenance helps protect your investment and keeps your treated timber looking great for years.
FAQs
What does H3 mean in timber?
It means the timber has undergone a treatment process for moderate outdoor exposure, providing resistance to fungal decay and insect attack when used above ground.
Can H2 timber be used outside?
No. H2-treated timber is designed for indoor applications. Using it in outdoor projects can result in decay and structural damage.
What happens if I use the wrong hazard level?
Using timber with the wrong treatment class can cause rot, moisture damage, and failure to meet Australian Standards.
Does Weatherproof treated timber need painting?
Yes – painting or staining adds an extra layer of protection and helps maintain a maintenance-free finish for longer.
Understanding and applying the correct timber hazard level is essential for every builder. By comparing H2 vs H3 timber and H3 vs H4 timber, you can ensure the treated pine you use matches the environmental exposure of your outdoor applications.
Choosing the right treatment improves durability, prevents decay, and ensures long-lasting performance.
Explore Woodhouse’s treated timber products and source everything you need for your next build from trusted building supplies. Visit Woodhouse Treated Pine to learn more.