Choosing the Right Timber
Timber Hazard Classes Explained.
The Hazard Class of timber indicates the level of treatment it has received to protect it from various hazards such as decay, moisture, and insect attack.
Understanding Hazard Classes
Choose the Right Timber for Your Environment
When selecting timber for your project, it’s crucial to ensure that the wood is not only treated but also suited to the specific conditions it will face. Timber displaying the WOODmark® stamp is a guarantee of quality, as it indicates the wood has been treated to the highest standards.
Alongside the WOODmark® stamp, you’ll also find the timber’s Hazard Class rating. This rating is key to understanding the level of treatment the wood has undergone, tailored to withstand specific environmental challenges. The dual marking ensures that you can easily identify both the quality of the treatment and its suitability for your particular environment.
What is a Hazard Class?
The Hazard Class of timber indicates the level of treatment it has received to protect it from various hazards such as decay, moisture, and insect attack.
These classes are marked as ‘H’ followed by a number (e.g., H1.2, H4) and are designed to help you choose the right timber for your environment.
How to Choose the Right Timber
When choosing timber, start by assessing the environment where the wood will be used. Will it be indoors or outdoors? Will it be exposed to moisture, ground contact, or even seawater? Use the Hazard Class rating to guide your decision, ensuring the timber you select is fit for the conditions it will face. This will help ensure the longevity and safety of your project, whether you’re building a deck, a fence, or a house.
By understanding and utilising the Hazard Class system, you can confidently select the right timber for any job, ensuring durability and compliance with industry standards.
Why Hazard Classes Matter
Whether you’re a professional specifying timber for a large construction project or a homeowner planning a DIY job, understanding Hazard Classes ensures that you select the appropriate wood for the conditions it will face.
Using the wrong class of timber can lead to premature failure, costly repairs, or even safety issues. Therefore, always check the Hazard Class rating on the timber you plan to use.
Understanding the Hazard Classes
Choosing the right timber for your project is crucial to ensuring its durability and safety. Each type of timber is treated to withstand specific environmental conditions, and these are classified by Hazard Classes. Below, we break down each Hazard Class, providing details on the types of preservatives used, the level of exposure the timber can handle, and the typical applications to help you make the best choice for your needs.
H1.1 - Low Hazard Situations
Typical Preservative: Boron
Exposure: Designed for indoor use, H1.1 timber is protected from the weather and remains dry in service. It’s primarily concerned with resistance to borer, making it perfect for environments where the timber isn’t exposed to moisture.
Typical Uses: Interior linings and trim where the timber remains dry.
H1.2 - Low Hazard Situations
Typical Preservative: Boron, Water Borne Azole
Exposure: This class is for timber that is protected from the weather above ground but may be exposed to occasional moisture, or insect attack from insects such as borer which could lead to decay.
Typical Uses: Ideal for wall framing, floor and ceiling framing, and roof trusses, where there is a slight risk of moisture exposure.
H2 - Termite Protection (Australia Only)
Typical Preservative: Boron, Water Borne Azole (with added insecticidal treatment)
Exposure: Similar to H1.2 but includes additional protection against termite attack. H2 timber is used in areas where termites are a concern, particularly in Australia.
Typical Uses: Timber framing and other interior uses where termite protection is required.
H3.1 - Moderate Decay Situations
Typical Preservative: Boron, Water Borne Azole, LOSP
Exposure: This class covers timber exposed to the weather above ground in non-structural applications. The timber must be painted and used in a vertical plane to ensure longevity.
Typical Uses: Perfect for exterior joinery, cladding, fascia boards, and cavity battens, where the timber is exposed to the elements but not in contact with the ground.
H3.2 - Moderate Decay Situations
Typical Preservative: CCA, Copper Quat, Copper Azole, Copper Naphthenate, Micronised Copper Azoles
Exposure: Timber in this class can be exposed to the weather above ground or be protected from the weather but still at risk of moisture entrapment.
Typical Uses: Ideal for decking, palings, handrails, and structural timber such as joists and bearers for decks and walkways, where moisture exposure is a concern.
H4 - High Decay Situations
Typical Preservative: CCA, Copper Quat, Copper Azole, Micronised Copper Azoles
Exposure: Designed for timber that is in direct ground contact or submerged in fresh water, where exposure to moisture is constant.
Typical Uses: Commonly used for fence posts, horticultural posts, garden edging, and other landscaping timbers where durability is key.
H5 - Severe Decay Situations
Typical Preservative: CCA, Copper Quat, Copper Azole, Micronised Copper Azoles
Exposure: This class is for timber exposed to severe conditions, such as continuous wetting in ground contact or fresh water in critical applications.
Typical Uses: Used for house piles and poles, retaining walls, horticultural posts in severe sites, and fresh water marinas, where the timber must withstand intense environmental stress.
H6 - Marine Environments
Typical Preservative: CCA
Exposure: Specifically treated to endure the harsh conditions of sea water or estuarine ground, where the timber is regularly immersed.
Typical Uses: Ideal for saltwater wharf pilings, marinas, and aquaculture applications, where the timber is exposed to constant immersion in saltwater.
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