Treated vs Untreated and understanding the UC (Use Class) System

Phil Bryant
Jul 2
4 min read

Choosing between treated and untreated timber is a crucial decision for any construction or DIY project. By understanding the key differences in treatment processes and their implications, you can make a more informed choice. This post will explore the details of timber treatment, focusing on Tanalith and Tanalised wood, so you can decide what best suits your needs.

What is Treated Timber?

Treated timber undergoes chemical processes to enhance its durability and protect it from decay, insects, and harsh environmental factors. The preservatives penetrate deep into the wood, allowing it to endure moisture and extreme weather conditions. This quality makes treated timber a top choice for outdoor projects, such as decking, fences, and garden structures.

Fun fact: Treated timber usually has a noticeable greenish hue, which comes from the chemical preservatives. Typically, treated timber lasts two to three times longer than untreated wood, providing homeowners and builders peace of mind.

What is Untreated Timber?

Untreated timber is wood that has not been chemically preserved, allowing it to maintain its natural appearance and texture. While it is generally more eco-friendly and easier to work with for some projects, untreated timber is particularly vulnerable to damage from insects, fungi, and moisture.

For indoor applications—like furniture and interior trim—untreated timber shines. However, when used outdoors, it faces risks such as early decay and frequent maintenance or replacement, which can add unexpected costs over time.

The Tanalith Treatment Process

Tanalith is a well-regarded wood treatment process that utilizes copper-based preservatives to protect timber against deterioration. During this process, a preservative solution is applied under pressure, ensuring that it deeply penetrates the wood fibers.

Benefits of Tanalith Treatment

Durability: Tanalith-treated timber resists fungal attack and insect infestation, making it perfect for outdoor use.
Longevity: This treatment can extend the life of the timber by up to 15–25 years, reducing the need for replacements.
Versatility: Tanalith-treated wood is suited for various applications, including landscaping, decking, and structural support.
Environmentally Friendly: While it uses chemicals, Tanalith adheres to environmental safety standards, allowing for responsible outdoor project use.

Understanding Tanalised Timber

Tanalised wood specifically refers to timber treated with Tanalith preservatives. This term denotes both the treatment process and the materials used for effective protection against environmental elements.

Characteristics of Tanalised Timber

Visual Appearance: Tanalised timber typically has a green or brown tint due to the treatment, making it visually identifiable.
Water Resistance: This type of timber naturally repels water, effectively reducing the risk of rot when placed outdoors.
Low Maintenance: Once installed, tanalised wood requires minimal upkeep compared to untreated timber, making it a time-efficient option for homeowners.

Comparing Treated vs Untreated Timber

Strength and Durability

Untreated timber may be viable for indoor applications, but its lack of protection means it is less durable than treated options. Tanalith-treated timber stands out due to its lasting qualities, allowing for long-term use without significant repairs.

Cost Effectiveness

Initially, untreated timber may seem like a cheaper option. However, when you factor in longevity and maintenance costs, treated timber like Tanalith often proves to be more economical over time. For instance, while untreated timber may cost around $3 per linear foot, treated timber can be closer to $6 per linear foot, but the latter reduces the need for replacements and repairs.

Environmental Impact

Untreated timber is a more sustainable choice for indoor uses, as it retains its natural state. Treated timber, while engineered for durability, involves chemicals that some environmentally-conscious consumers may prefer to avoid. It’s essential to weigh the pros and cons based on your specific use case.

Understanding the UC (Use Class) System

All types of timber have a UC rating, this allows the user to identifiy if the timber is suitable for the project in mind:

UC1: Timber used indoors with no risk of wetting, such as interior structural timber.

UC2: Timber used indoors with a chance of occasional wetting, such as bathroom fittings.

UC3: Timber used outdoors, above ground, and exposed to the weather, such as fencing and cladding.

UC4: Timber used outdoors, in contact with the ground or freshwater, such as fence posts and decking joists.

UC5: Timber used outdoors, regularly submerged in seawater.

Selecting the right timber for a specific application:

Choosing the correct Use Class ensures the timber is adequately protected for its intended environment, maximizing its lifespan.

Determining the appropriate treatment:

Different Use Classes require different levels of preservative treatment to prevent decay and insect damage.

Ensuring the long-term durability of timber structures:

By understanding the Use Class system, you can make informed decisions about timber selection and treatment, leading to more robust and long-lasting structures.

Final Thoughts

When choosing between treated and untreated timber, it’s vital to consider the specific needs of your project. Treated timber, particularly Tanalith and Tanalised wood, offers remarkable durability and extended lifespan, making it suitable for outdoor uses. Conversely, untreated timber is an excellent option for indoor projects that prioritize natural aesthetics.

Ultimately, your choice should align with your project's requirements. By understanding the differences between these types of timber, you can ensure successful results in your next venture. Whether you lean towards the long-lasting benefits of treated timber or the natural appeal of untreated wood, being informed is key to satisfaction in your selections.