Chemically Treated vs Thermally Treated Cladding: What’s Best for Your Build?
- Thermally treated timber uses high heat to improve moisture resistance and stability
- Chemical treatments like LOSP and CCA protect against insects, rot, and decay
- Thermally treated cladding is eco-friendly and low maintenance
Choosing the right timber cladding for your home or commercial project isn’t just about looks, it’s about long-term performance, durability, sustainability, and value. At Villaworx Construction, we work with a range of high-performing materials, and two commonly discussed treatments for timber are chemically treated and thermally treated claddings.
Understanding the difference between these two methods, and the pros and cons of each, will help you make a more informed decision that suits your build, budget, and environmental goals.
What is Thermally Treated (or Thermally Modified) Cladding?
Thermally treated timber is natural wood that has been modified using high temperatures (typically over 180°C) in a controlled, low-oxygen environment. This thermal modification process alters the structure of the timber’s key components, such as lignin, cellulose, and hemicellulose, reducing its ability to absorb moisture. As a result, the wood becomes less prone to swelling, shrinking, or warping and gains impressive dimensional stability.
Because oxygen is restricted during heating, the wood doesn’t ignite, even at high temperatures. Various thermal modification methods exist, such as steam, nitrogen, or hot oil. However, it’s important to note that while thermal treatment boosts durability, it can slightly reduce the timber’s natural strength and flexibility depending on the process used.
Leading NZ Suppliers of Thermally Treated Cladding:
What is Chemically Treated Cladding?
Chemically treated cladding is timber that has been infused with preservatives to improve its performance outdoors. These treatments help protect the wood from rot, insects, and fungal decay, making it highly suitable for cladding and other exterior applications.
Popular treatment types include:
LOSP (Light Organic Solvent Preservative): A low-moisture treatment that helps retain the timber’s natural appearance.
CCA (Copper Chromium Arsenate): A long-established method that offers deep, long-lasting protection.
Chemical treatments come in various levels depending on exposure risk, higher grades are used for harsher conditions or ground contact applications.
Thermally Treated vs Chemically Treated Cladding: Pros & Cons
| Feature | Thermally Treated Timber | Chemically Treated Timber |
|---|---|---|
| Durability | Highly resistant to decay, moisture, and pests; performs well in NZ’s varied climate | Excellent protection depending on treatment level, especially against rot and insects |
| Appearance | Rich, natural tone that weathers beautifully; no chemical smell | Often retains natural grain; some treatments may darken timber or leave a slight odour |
| Sustainability | Chemical-free, environmentally friendly process | Involves synthetic preservatives; disposal must be managed responsibly |
| Maintenance | Low maintenance; may benefit from UV oil for colour retention | Most treatments require resealing or painting depending on exposure |
| Strength | Slight reduction in structural strength due to high heat | Maintains structural integrity unless overexposed to moisture |
| Cost | Typically higher upfront cost due to specialist process | Generally more affordable, especially for large-scale builds |
| Health & Safety | Safe to handle; no chemical leaching | May require PPE during cutting and proper handling/disposal |
Which one should you choose?
Both cladding types offer excellent performance, but the right choice comes down to your priorities:
- Choose thermally treated if you value sustainability, reduced maintenance, and are looking for a chemical-free solution with a modern, natural aesthetic.
- Choose chemically treated if budget is a major factor, or you want a larger variety to choose from..
At Villaworx Construction, we work with both material types and can recommend the best fit for your specific project, from architectural homes to long-lasting renovations.
Contact Villaworx Construction today to chat about cladding options or request a project consultation. We’ll help you navigate your options and bring your vision to life with expert craftsmanship and trusted materials.