What is yakisugi

The story of burning timber cladding is centuries old.

Traditionally Yakisugi (Shou Sugi Ban ) is a fence, ceiling or weatherboard cladding made exclusively from Japanese Cypress (Japanese Cedar). This process started over 600 years ago to improve the life of Japanese homes. Like all building materials over time we discover new way and new better materials to produce a product. As such modern charred timber cladding is made from a wider range of timbers each giving different characteristics. Fire conditioning these timbers under immense heat serves as a preservative and has a stabilising effect on the wood.

How is Shou Sugi Ban made?

Historically, charred wood cladding has been made by the Japanese contractor on each jobsite. The contractor would create a 3 board chimney and light a fire inside the chimney. Each chimney would need to be rotated and for a second fire in the opposite end to ensure even charring along the length of the timber. As you can imagine this was a long and slow process.

Only in the last several decades has charred timber manufacturing transitioned to timber mills and professional shou sugi ban manufacturers like us. This is due to the demands of Architects and the need for highly consistent production quality of the construction market. In Japan a holistic and narrow manufacturing protocol has been developed over hundreds of years to ensure dimensional stability and maximum longevity, which we have studied replicated in New Zealand.

The fire conditioning is intense, and the charred wood is quenched at the perfect time. Then it is dried again so the timber is ready for the customer in the charred Suyaki finish. Or the charred timber is cooled then brushed to remove charred layer to reveal the textural beauty to achieve the desired appearance. Standard traditional products include Suyaki (original charred), Gendai (brushed once), and Pika-Pika (brushed twice).

How does Charring timber work?

The heat treatment improves timber cladding longevity by preventing decay and insect infestation, it also makes the boards more dimensionally stable, and improves fire retardancy.

Wood is predominately made of structural lignin, with hemi-cellulose carbohydrates which are food for fungi and insects. Fire conditioning of timber cladding burns off the cellulose, removing the primary food type and minimizing rot and infestation. The charred wood treatment also case hardens the timber, and in combination with air drying, improves dimensional stability in severe weather exposure. How charred wood becomes more fire resistant is that the charred layer increases the temperature threshold needed for combustion, significantly reducing flame spread. The charred layer is also a natural hydrophobic (repells water) protection against weathering.

Does the wood truly become a no-maintenance timber product?

In Japan the answer is yes. In New Zealand Not always. What effects the oil maintenance requirements is primarily the species of timber selected. There is a 1 timber type that never requires oil maintenance, and for other timbers this is a very low maintenance finish which only needs to be re-oiled at least every 5 years to slow down the weathering process.

All charred wood cladding surfaces start off with the boards being deeply charred to about 1 - 1.5mm of char.

From there we either oil coat the boards for out suyaki finish, or brush the boards to achieve the Gendai finish. The Pika-Pika finish is brushed again. Suyaki’s thick char layer will keep the same colour for a very long time depending on burn quality and site environmental conditions. However, the Gendai and Pika-Pika brushed surfaces will weather over time and we advise a 3-5 year oiling cycle for a smart appearance.

With charred wood cladding we must differentiate between wood and colour longevity. While heat treatment preserves the wood, with brushed finishes a re-oiling schedule is necessary to maintain colour. We recommend you live with your charred wood cladding for several years before considering re-oiling, given the chance you will enjoy how the product develops a rich patina with time — not to mention avoiding the unnecessary maintenance costs.

Which types of timber are best for Shou sugi ban cladding?

Many timbers are excellent for charring, but some are not suitable as the char layer is too soft and its charred face falls off very quickly. Sone timbers are poor charred but stunning charred and brushed. Below is our preferred timbers for charred timber cladding and charred and brushed.

The ideal characteristics we look for are straight-grained, fast-drying, tannin-rich, stable and strong timber— very much all desirable characteristics for timber cladding. Most importantly a thick, dense latewood growth ring, which burns to a more substantial, longer-lasting char layer. Many timbers in the cypress family have chemical properties that respond well to fire, and it becomes incredibly dimensionally stable when milled, dried, fire conditioned in the traditional Japanese way.

In Japan the largest forestry company who produces Yakisugi is Nakamoto forestry, and they will only use Japanese Cedar.

Our experience has shown that many hardwoods promise greater longevity, but do not char well with very high density but there are some very options.

If you are looking at these alternatives, we stress that you must take the long-term perspective. We trust our cladding to look great without any maintenance for its lifetime in New Zealand.

Best wood types for charring.

Accoya
Alto
Templewood
TMT Pine
Japanese Cedar
Blue Gum
Siberian Larch

Best wood types for char and brush.

Siberian Larch
Accoya
Western red cedar
Templewood
Japanese Cedar
TMT Pine
Lawson Cypress
Californian Redwood