Shou sugi ban (yakisugi, 焼杉) is a traditional Japanese technique of charring cedar to preserve it. The outer layer of char seals the wood against moisture, insects, and fire.
The method: burn the surface until it's deeply charred (3–5 mm), then brush off the ash, revealing a stable carbonized surface. The carbon is inert and resists biological decay.
Properly done, yakisugi exterior cladding lasts 80–100 years without treatment. The aesthetic — dark, textured, weathering to silver-gray — has become fashionable in contemporary architecture.