2nd Apr 2024 -

The construction industry is under pressure to adopt sustainable practices across all operations. One innovative solution that is gaining traction is the use of treated timber. Treated timber boasts strong durability and aligns with the principles of eco-friendly construction. This feature outlines the potential of treated timber, exploring its unique properties for sustainable building projects. 

What is treated timber?

Treated timber is wood that has undergone chemical or physical treatment processes. These aim to enhance its durability, resistance to decay and overall lifespan. Also, treatment processes ensure it withstands environmental conditions, insect infestations and fungal issues. 

These issues can compromise its structural integrity and shorten its lifespan. Treated timber is used in various applications, including residential, commercial and industrial projects. It is commonly used for outdoor structures such as decking, fencing, landscape features and garden furniture. 

In some cases, treated timber is used for structural components such as posts and framing. Below are several methods used to treat timber.

  • Pressure-treated timber: Also known as tanalised timber, this method involves forcing preservative chemicals deep into the wood under high pressure. Timber pressure treated materials offer protection against rot, insects and fungi.
  • Heat-treated timber: In this process, wood is exposed to high temperatures. This alters its chemical composition and makes it more resistant to decay and dimensional changes.
  • Acetylated timber: Acetic anhydride is used to chemically change the wood. It replaces free hydroxyl groups and enhances its durability and dimensional stability.

You can read more about treated timber with our comprehensive guide.

Which treatment is most sustainable?

When comparing the sustainable properties of each treatment option, there is no one-size-fits-all approach. Each method has its benefits and drawbacks. The most sustainable choice depends on various factors. Here is a breakdown of the sustainability considerations for each treatment.

Timber treatmentSustainability factors
Pressure-treated timber - Commonly treated with copper-based preservatives like alkaline copper quaternary (ACQ) or copper azole (CA-B). 
 - Copper is a naturally occurring element. It is less toxic than alternatives like chromated copper arsenate (CCA). 
 - Effective against fungal decay and insects. 
 - Potential for copper leaching over time, which can impact soil and water quality.
- Allowing the timber to air dry is more environmentally friendly. Kiln-drying requires energy input, typically using electricity or fossil fuels.
Heat-treated timber - Sustainable treatment process that uses high temperatures.
 - No chemical preservatives used, reducing toxicity concerns.
 - Improved dimensional stability and resistance to rot and insects.
 - Higher production costs and energy consumption during heat treatment.
 - Limited effectiveness against wood-boring insects.
Acetylated timber- Treated with acetic anhydride, a non-toxic chemical derived from plant biomass.
- Highly durable and dimensionally stable due to decreased moisture absorption.
- No potential for toxic leaching or environmental contamination.
- Energy-intensive acetylation process, resulting in higher embodied energy.
- Limited availability and higher costs compared to other treated timber options.

Why is treated timber more sustainable? 

A treated timber batten or board offers a range of sustainable pros. This makes it an attractive choice compared to untreated timber, steel and concrete. These benefits contribute to environmental preservation and boost resource efficiency. 

1. Renewable and carbon-sequestering

Treated timber is developed from renewable wood sources that can be sustainably managed and replenished through responsible forestry practices. The timber-treating processes do not alter the renewable nature of the wood material itself. 

Also, the carbon isolated by the living trees remains locked within the preservative-treated wood even after processing and construction. This directly offsets greenhouse gas emissions throughout its lifetime compared to non-renewable materials like steel and concrete.

2. Energy efficiency

​​While all wood provides natural insulation value, chemically treated timber offers enhanced energy efficiency benefits. This is because of its increased resistance to moisture, rot and insect damage over time. For example, untreated wet wood is more susceptible to these elements which can degrade its insulative properties. 

Treating the wood with preservative compounds like CA-B or ACQ extends the thermal performance. Properly treated carcass timber framing, siding and roof materials maintain superior insulation capabilities for longer periods compared to untreated wood. 

3. Recyclability

Properly treated timber can last 20-50 years or more before replacement is needed because of its rot and insect resistance. This longevity cuts down on material waste. After use, treated wood can be recycled into products like landscape mulch and wood-polymer composites. 

4. Low embodied energy 

The embodied energy of timber accounts for the energy used in extraction, transport, manufacturing and installation. Because wood requires relatively little processing compared to energy-intensive materials like steel and concrete, treated timber has lower embodied energy. This is around 3.5 megajoules per kilogram (MJ/kg) vs over 30 MJ/kg for steel.

5. Design versatility

Treated carcassing timber can be used for structural framing, deck and fencing areas, outdoor furniture and decorative interior elements. This offers many sustainable options. Its workability allows for complex designs, decorative finishes and integration with other natural materials not possible with concrete or steel.

How to improve sustainability with treated timber

Treated timber offers durability, longevity and reduced maintenance to minimise the need for frequent replacements. By incorporating treated timber, you contribute to the overall sustainability of a building project. Here are some specific considerations and steps to follow. 

Choose the right treatment process

Select timber treated with eco-friendly preservatives that are free from harmful chemicals like chromium, arsenic and creosote. Alternatives such as CA-B and ACQ treatments are more environmentally friendly and can extend the lifespan of timber without compromising its structural integrity.

Understand application suitability

Different timber treatment processes are suitable for specific applications. For example, CA-treated timber is ideal for above-ground applications like a deck area, a garden fence and outdoor furniture. At the same time, ACQ is suitable for both above-ground and ground-contact applications, such as a fence post or framing structures.

Maximise lifespan with maintenance 

Regularly inspect treated timber for signs of deterioration, such as cracks, splits or rot. Apply coatings or sealants to protect the timber from moisture, UV radiation and other environmental factors that can accelerate degradation. Also, using paint or stain products helps enhance its appearance and offers protection against decay. 

Consider reuse and recycling

When possible, prioritise the reuse of treated timber components from demolition or renovation projects. If reuse is not feasible, explore recycling options for treated timber. Preservatives used in timber treatments are less hazardous and can be safely disposed of or recycled.

Responsible sourcing

Make sure to source treated timber from suppliers who practice sustainable harvesting practices. Look for certifications like Forest Stewardship Council (FSC) which ensure that the timber is sourced from well-managed forests.

Boost design and construction

Seek advice from architects and designers to optimise the use of treated timber in construction projects. Explore techniques like prefabrication, modular construction and efficient material use. This will minimise waste and increase resource consumption.

Sawn vs CLS: Which is more sustainable?

The choice between CLS treated timber and treated sawn timber can have significant implications. Both options offer durability and longevity. However, they differ in their manufacturing processes and environmental impact. Below is a comparison to help determine the more sustainable option.

CLS treated timber

CLS treated timber is manufactured by sawing logs into standard sizes and then subjecting the pieces to pressure treatment with preservatives. This process offers several sustainability benefits.

  • Efficient material usage: CLS timber production maximises the use of raw materials by converting logs into standardised sizes. It reduces waste and ensures optimal resource utilisation.
  • Consistent quality: The standardised manufacturing process ensures consistent quality and dimensional accuracy. This lessens the need for rework or replacement because of defects.
  • Lower transportation emissions: CLS timber is often produced closer to the construction site. It reduces the carbon footprint associated with transportation over long distances.
  • Recyclability: At the end of its lifespan, CLS treated timber can be recycled or repurposed. This further contributes to a circular economy and reduces the demand for newer materials.

Sawn treated timber

Sawn treated timber is produced by sawing logs into various sizes and edge profiles, often customised to dimensions. While this approach offers flexibility, it may have some sustainability drawbacks.

  • Higher material waste: The process of sawing logs into custom sizes can result in more material waste compared to the production of CLS timber.
  • Inconsistent quality: Quality and dimensional accuracy of rough sawn treated timber can vary. It potentially leads to higher rejection rates and added material consumption compared to CLS and planed treated timber. 
  • Longer transportation: Sawn treated timber may need to be sourced from more distant suppliers. This increases the transportation emissions.
  • Limited recycling potential: Because of the variability in sizes and dimensions, sawn treated timber may have limited opportunities for recycling or repurposing at the end of its lifespan.

Is treated timber available at Building Materials Nationwide?

Yes. We are your one-stop shop for treated timber, from sawn treated timber to green treated timber battens. Our selection is available in various dimensions and grades, making it suitable for framing, structural components and more. Whether you need to buy C16 treated timber or C24 treated timber, we offer top sustainable solutions.

We welcome trade customers to open trade accounts with us, providing a range of benefits tailored to your needs. By opening a trade account, you gain instant access to competitive trade pricing, dedicated account management and quick UK delivery options. Opening a trade account ensures access to high-quality materials and exceptional customer service. Sign up today or contact the team for a chat.

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