Flame Treated Wood

The use of flame treated wood by humans stretches nearly as far back in history as the use of wood itself. People first began modifying wood with fire around 400,000 years ago, using flames to harden the points of wooden spears, arrows and other tools. The exact origin of learning to use fire has been lost to time, though archaeological evidence confirms that nearly every early human civilization used various methods of heat treatment to manipulate wood.

The Clacton Spear is the tip of a 450,000-year-old fire-hardened spear discovered in England.

History of Flame Treated Wood

Many cultures have specific wood burning practices that have survived from ancient times to this day. While the methods may have been modified as modern materials and energy options have been discovered, some historic records exist that can help us understand how wood burning methods have evolved over time. In some cases the traditional techniques are still practiced today.  

Early man moved on from simply using fire to cook, keep warm and make crude tools. We began to find other uses for burning wood. The vikings learned to overcome the shortcomings of natural wood by treating it with fire centuries ago. We used fire to burn the bottoms of fence posts to make them more durable to pests and rot. Soon cultures around the world were burning the bottoms of boats for the same benefits. We began experimenting with using heat and steam to make wood more pliable. Using heat to manipulate boards of wood helped leapfrog technology, ship building and architecture forward. Eventually, the use of fire to make wood planks more pliable for boats and houses became commonplace around the world.


In Asia, the traditional process of bending wooden boards for boats over an open fire is called yakimage. Its origin is unknown, but it is one of the most widespread methods of flame treated wood in history. When done properly, the inside of the wood curve becomes charred over the open flame after hours of thoroughly heating the wood enough to bend. The outside of the hull remains intact and the finished boat will have floorboards that cover the burned inside. Still, it’s common to have significant charring on the inside of the curved hull. Eventually this method was surpassed in popularity by the use of steam to bend the boards.

Yakimage: Using fire, a lever and gravity to slowly bend the boards of a ship. Image source.

Architectural Beginnings

On our most recent trip to Japan we visited the coastal town of Tomonoura. A local museum informed us that many of the town’s historic structures were originally constructed using dismantled boat materials. As we walked through the surrounding streets, we came across multiple homes clad with boards that were curved and warped outward, like the hull of a ship. They were also burned on the outside, which would have been the inside of a boat hull.

It seems that early settlers in coastal areas of Japan may have reused the boards from their boats for buildings. When fires ravaged the towns, they noticed that the buildings constructed using flame treated wood from their ships didn’t catch fire. Putting the pieces together, they developed the flue method of burning wood specifically for siding. Enter the yakisugi, or “shou sugi ban” of today.  

The Benefits of Flame Treated Wood

Using the traditional flue method to burn our own yakisugi siding.

The use of fire on wood surfaces serves several purposes. First and foremost, it makes catching fire again much more difficult. The Edo period in Japan (1603-1867 A.D.) was marked by savage fires destroying a number of villages and towns. Building homes from stone or stucco was expensive and typically reserved for those in the upper class. For farmers and the working class, using siding that had already been charred (shou sugi ban, yakisugi, or yakisugi-ita) helped reduce the risk and damage from fires during this time. 

Second, flame treated wood is incredibly resistant to pests. The cellulose and hemicellulose layers of wood are burned off when exposed to flame. This leaves behind a surface that doesn’t have any food available for insects. Carpenter ants, termites and other critters leave it alone and move onto the next food source.

Third, flame treated wood is more durable and weather resistant than untreated wood. Normal timber would begin to rot or warp due to moisture given time. Charred wood will withstand the elements for far longer before it needs to be replaced. The soot layer also acts as a UV inhibitor, keeping the wood fibers from degrading under harsh sunlight. 

Yakisugi in Modern Life

Throughout its long history, burned wood has proven itself to be an indispensable tool when it comes to building structures. Its durability and longevity, coupled with its aesthetic appeal means it’s a great choice when it comes to cladding your home.

Additional Resources

Want to learn more about shou sugi ban? Get started with one of our related posts!

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DIY: Burning Yakisugi by the Traditional Japanese Flue Method

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