The story of shou sugi ban (yakisugi) goes back centuries.
What is Yakisugi or “shou sugi ban”?
Yakisugi is wall and ceiling cladding made exclusively from cypress and intensely burned as a preservative heat treatment through a traditional Japanese process.
What isn’t Yakisugi?
Yakisugi is a thin-plank product only used for wall, fence, and ceiling cladding, not a burning technique or surface treatment. It is never made from reclaimed wood, driftwood, or chemically treated wood. We have only had good results using Japanese Cypress. Yakisugi cannot be replicated without the traditional drying and contained heat treatment process. It is not burned with a torch, kiln dried, made from tongue and groove profile, burned on both faces as standard, or burned after installation.
Yakisugi or “shou sugi ban” are finished products, not a verb or adjective.
How is shou sugi ban made?
Historically, shou sugi ban has been made by the project general or siding contractor on each jobsite. Only in the last several decades has yakisugi manufacturing transitioned to lumber mills such as us due to modernization of the construction market. A holistic and narrow manufacturing protocol has been developed over hundreds of years to ensure dimensional stability and maximum longevity.
The process starts off with careful log selection, grading for straightness and diameter, grain density and quality, and wood color. The logs are resawn plain or quartersawn only, and the moulder blanks are air or sun dried, not by kiln. The heat treatment is intense and the wood is quenched at the right moment. After drying again, the wood can be used as-is or brushed to knock down the soot layer in order to achieve the desired appearance. Standard traditional products include Suyaki (original charred), Gendai (brushed once), and Pika-Pika (brushed twice).
How does the heat treatment work and does the wood truly become a no-maintenance siding?
The heat treatment improves siding longevity by preventing decay and insect infestation, makes the planks more dimensionally stable, and improves fire retardancy. Yakisugi is a maintenance-optional exterior wood siding, either re-oiled periodically to slow down the weathering process, or simply replaced after its lifetime is reached.
By weight wood is mostly structural lignin, with a balance of hemi-cellulose carbohydrates that are food for fungi and insects. Heat treatment of yakisugi burns off the cellulose, minimizing rot and infestation. The heat treatment also case hardens the planks, and in combination with air drying, reduces dimensional movement in severe weather exposure. The soot layer increases the temperature threshold needed for combustion, dramatically reducing flame spread, while also adding a hydrophobic protection against weathering.
All yakisugi surfaces start off with the planks being deeply heat treated to Suyaki. They can then be brushed next to achieve Gendai and Pika-Pika style surfaces. Suyaki’s thick soot layer will keep the same color for 40 to 80 years depending on burn quality and site conditions. However, the Gendai and Pika-Pika brushed surfaces will weather in color same as any kind of wood material.
It is important to differentiate between wood and color longevity. While heat treatment preserves the wood, a re-oiling schedule is necessary to maintain color. In Japan, the “sabi” patina is valued for its beauty. We ask our customers to live with their siding for several years before considering re-oiling, given the chance they will enjoy how the product develops a rich patina with time — not to mention avoiding the unnecessary maintenance.
What makes Japanese Cypress best for yakisugi?
Though hinoki cypress, pine, larch, oak, camphor, and other species are abundant in Japan, yakisugi is exclusively made from sugi cypress. Cypress is straight-grained, fast-drying, flexible, tannin-rich, and strong—all desirable characteristics for siding. Critically, it has a thick, dense latewood growth ring, which burns to a more substantial, longer-lasting soot layer. Compared to other species, cypress’s chemical properties respond well to fire and it becomes incredibly dimensionally stable when milled, dried, burned and quenched by traditional protocol.
Our traditional Japanese heat treatment process requires the use of Japanese cypress. Despite access to quality affordable Siberian Larch and being the largest Radiata Pine timberland owner in New Zealand, Japanese Cypress remains our material of choice. While hardwoods or chemically modified woods with faux finishes might promise greater longevity, we have found that none live up to our environmental standards or respond appropriately to our traditional process.
When considering these alternatives we can’t help but take the long-term perspective. Cypress is time-tested by centuries of Japanese tradition. We trust our siding to look great without any maintenance for its lifetime. Chemically treated wood, hardwoods, or faux finishes will always weather inconsistently.
“Yaki” means burnt, charred, or heat treated, and “Sugi” refers to the Sugi Cypress indigenous to Japan
What is the difference between Yakisugi and Shou Sugi Ban?
The heat treatment of wood has been common around the world in various applications for millennia. Japanese yakisugi is only one of many variations and has very specific manufacturing parameters and applications. Yakisugi is thin-plank wood siding and paneling heat treated in a traditional Japanese process. Unfortunately yakisugi has been mis-labeled as “shou sugi ban” in the West due to poor translation. At the same time there is common misunderstanding of what yakisugi actually is, how it is made, and what applications it is suitable for.
“Yaki” means burnt, charred, or heat treated, and “Sugi” refers to the Sugi Cypress indigenous to Japan (often called “Japanese Cedar”). So, “Yakisugi” translates to “charred cypress”, “burnt cedar”, or “heat treated cypress”. The term “shou sugi ban” likely originated in the early oughts, and is a combination of Japanese and Chinese pronunciations of the ideographs used for the term yakisugi. “Shou sugi ban” is a mistaken mixture of Chinese and Japanese. The word is not even recognized or understood in Japan.
As burning treatments have become more popularized online, there have been a proliferation of products, both DIY and retail, labeled as shou sugi ban. These instances mistake yakisugi, or shou sugi ban, as a method or a verb, which it is not. While any wood can be burned as a surface treatment, there is a holistic manufacturing protocol that must be followed in order to produce (via dramatic transformation by fire) straight, long-lasting, and beautiful yakisugi planks suitable for exterior application under harsh elements.
According to traditional protocol yakisugi can only be made from sugi trees. While heat treatment works well on many types of wood, such as low-temperature thermal modification of various species by the Finnish process, cypress works best for the Japanese high-heat, thin-plank cladding technology. In order to achieve a high yield of planks that are long, straight, and flat enough to install on an exterior wall plane, and will hold a consistent surface appearance and structure over the long term, a holistic manufacturing process must be followed.
We start with careful log selection, intentional millwork, and atmospheric drying. Resaw pattern must be through and through, not random. Square edge or shiplap profiles must be used, not T&G or dutch lap. For proper heat treatment there must be a contained fire to reach the temperature necessary to burn off hemi-cellulose, and therein thermally modify the wood surface. A weed burner does not generate enough intense or prolonged heat for thorough, consistent heat treatment. A similar appearance can be achieved initially, but the poor quality of the soot layer allows for premature weathering.
Burning the surface of any dimension of most materials will probably make them hydrophobic and case hardened. However, burning wood to the high heat as done in Japan makes dramatic moisture content differences core to surface on material more than around 9/16” (15mm) thick, causing thicker stock to dramatically warp and twist. Very large timbers may not move in the same way and probably respond with a positive surface preservative effect, but this practice does not occur in Japan and is not yakisugi. Surface treatment of furniture or artisan applications is beautiful and fun (we love it), but is also not yakisugi.
What is Yakisugi’s architectural history?
Heat treating wood has been practiced by humans worldwide for millennia, every region seeming to have its own application and practice. The exact historical background of heat treated siding in Japan has not been confirmed, but our research indicates that Japanese plank burning technology transferred to siding application from boat building traditions along the Seto Inland Sea. Boats were built on dry docks, and their hulls were burned as a preservative before launch. Cypress production fed both architectural and boat building applications while carpenters worked between the two related industries.
Traditionally in Japan yakisugi is combined with white stucco on exterior walls, each region having a different design aesthetic. Today it is used in residential, commercial, and institutional applications as a healthy, sustainable, and beautiful alternative to inorganic, carbon-intensive modern materials. It is installed as exterior siding either vertically or horizontally, and is also used as exposed roof deck, soffit, and interior wall and ceiling paneling.
Japan has influenced western thought and design for 150 years, and yakisugi has significantly contributed to modern architecture in the form of the contemporary black monolithic wall aesthetic. Yakisugi material itself is finally starting to be accepted worldwide as a sustainable and cosmetically desirable wood cladding option. It has often been interpreted as a chic, high-design building material, but in its home market it is standard, utility wood siding, with improved longevity over untreated wood.