What is shou sugi ban?

Shou sugi ban is a Japanese technique in which the surface of timber is deliberately charred to create a protective layer of char. In Japan the technique is called yakisugi (焼杉, “burnt cedar”). “Shou sugi ban” is a Western reading of the same characters (plus 板, board) that has become the usual name outside Japan. The original timber was sugi, Japanese cedar (Cryptomeria japonica).

How it works

Burning the wood briefly and fiercely chars the outer layer. That char layer:

• protects against UV, so the wood beneath does not turn grey
• reduces water uptake at the surface
• gives the wood a deep black, crackled or silvery look, depending on the finish

After burning, the wood is brushed. The harder you brush, the more char is removed and the more the grain shows: from deep black and rough (unbrushed) to a smooth, lustrous texture in which the softer growth rings sit lower. The wood is then usually oiled, which fixes the char.

In Europe, larch, Douglas fir and cedar are often charred, alongside (imported) sugi.

Important: not fireproof

It is often claimed that charred wood is fire-safe. That is not true as a general rule. Charred wood is still wood and still combustible. The fire classification depends on the specific product, species, thickness and installation. Where the facade must meet fire requirements, ask the supplier for the tested classification.

Application and tips

• Install with a ventilated cavity. Fix the boards to battens with an air gap behind, so they can dry from both sides
• Use stainless steel screws or nails. Ordinary steel can cause black streaks and rust, especially in tannin-rich timber
• Choose enough thickness. Thin boards warp during burning, and the char layer eats into the section
• Burning it yourself? Mind safety. Work outdoors, away from combustible materials, dry grass and buildings, with an extinguisher to hand. Burn evenly in passes, and let the wood cool completely before stacking it
• Expect soot. Unbrushed boards rub off black when touched at first. Choose brushed and oiled boards wherever people or children walk past the facade
• Maintenance. Oiled finishes need re-oiling from time to time; how often depends on exposure and product

Related terms

• Cladding
• Larch wood
• Douglas fir wood
• Stainless steel
• Fire classification
• Open-jointed cladding system

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