What do you know about thermally modified wood?

With so many types of wood available, each crafted for specific purposes, choosing the right one can feel overwhelming. Not all of them are simple untreated softwood and hardwood lumber. Some of them have been specially modified to enhance their durability, stability or appearance. One of these modified lumber types is called thermally modified wood. But what exactly is thermally modified wood? What are the pros and cons of thermally modified wood decking and thermally modified wood siding? Are there any particular problems specific to thermally modified wood and how much does it cost? Let’s break it down and get to the heart of the matter.

What is thermally modified wood?

As the name suggests, this is a process that uses heat to change the wood. Thermal modification involves heating wood in a controlled environment to high temperatures of approximately 320-450°F degrees C with very little or no oxygen. This process completely transforms the wood’s chemical structure by breaking down hemicellulose and extracting moisture. Hemicellulose is something that feeds fungi that causes decay in wood.

What does thermal modification do to wood?

Thermal modification increases the durability of softwood by making it more resistant to decay, insects and fungi. Thermally modified wood is also more stable than traditional softwoods because after thermal modification, the wood absorbs less moisture, so it doesn’t swell, warp or shrink like untreated wood might. This makes it a good choice for high-temperature spaces like saunas and also in outdoor and humid environments.

A side effect of thermal modification is that it turns the wood richer and darker in tone. While initially thermally modified wood has a richer and darker color, over time, when exposed to UV rays, it will turn a silver-grey patina, just like untreated woods. To maintain the darker color, a UV-protective finish will need to be applied regularly.

Thermally modified wood decking

Thermally modified wood has many uses. It is extensively used for external decking due to its improved stability, durability and increased resistance to moisture, warping and swelling. Also, being exposed outside, often under harsh conditions, the thermal modification process makes it more resistant to the elements, insects, water ingress and rotting. Thermally modified decking is eco-friendly as only heat and steam is used in the modification process.

Thermally modified wood problems

Thermally modified wood does however come with a few drawbacks. Despite being stronger and more durable than untreated softwoods, thermally modified wood problems include:

• In comparison to Accoya, thermally modified wood can be brittle and weak, meaning it may not be strong enough for higher load-bearing use.
• Moisture can still be absorbed into the wood which, over time, can cause splitting and cracking.
• The darker tone created by the thermal modification process can actually fade in time meaning a UV protective treatment will be needed for exterior applications.

Thermally modified wood price

Budget often comes into play when specifying building materials, especially lumber, so the thermally modified wood price point is important. All said and done, is thermally modified wood a cost-conscious value choice? The answer is that everything is relative. Untreated softwood is cheaper than thermally modified wood, however, softwood doesn’t have the strength and durability. Does that make thermally modified wood the ideal choice? To make the best choice, you need to consider performance, maintenance, and long-term value. That’s why Accoya deserves a spot in the comparison.

What is Accoya?

Accoya is a modified wood, but instead of undergoing thermal modification, it is transformed through a unique acetylation process. This process alters the wood at a molecular level, enhancing its durability and stability and maintaining its natural beauty, strength and character. Made from fast-growing, certified sustainable timber, Accoya is one of the few building materials to achieve Cradle to Cradle Gold certification, with a Platinum rating in material health.

Although technically a chemically modified wood, Accoya is non-toxic, as its process increases the naturally occurring levels of acetic anhydride, rather than introducing harmful substances. The result is a high-performance wood with superior dimensional stability and durability, surpassing thermally modified wood alternatives.

Thermally modified wood vs Accoya

Whilst Accoya is more premium in price, when you put thermally modified wood vs Accoya head-to-head, Accoya does has several significant advantages:

•  Accoya acetylated wood has far superior, strength, durability and long-term value and it is backed by an unrivalled 50-year above ground warranty for wood durability.
• Compared to thermally modified wood, Accoya offers exceptional stability with minimal shrinking, swelling or warping – ensuring that boards arrive straight and stay straight.
• Accoya performs highly in wet conditions and is ideal for decking, siding, windows, doors and even swimming pools.
• Accoya is manufactured in the United States and is sustainable with FSC® Accreditation and Cradle to Cradle Gold certification™. It is also the only construction material in the world to achieve C2C Platinum certification™ for Material Health.
• Tests with thermogram images showed that Accoya wooden decks stay pleasantly cool, even on the hottest days. Accoya performed significantly better than comparable decking materials.

Accoya or Thermal Modification? The Smart Choice is Yours

You have heard the pros and cons of thermally modified wood vs Accoya, but ultimately, you need to make the choice between higher performance, longevity, sustainability and durability vs good performance, shorter lifespan and a lower price.

To see Accoya in real-life, visit a location near you.