Yakisugi Aesthetics and Sustainability

Lately, I have become fascinated with the super dark black wood siding that I see on buildings along the rural highways of upstate New York. I find the very dark tones to provide an earthy grounding effect and know that the wood itself makes a connection to the forests of these Catskill Mountains. In some cases, there is also black standing seam metal roofing, which creates a uniform effect between the walls and roof of the building. I’ve also been going through my material research catalogue of samples from the lab in past years and have a handful of material samples consisting of biochar. These samples are made from burning bamboo or other natural materials.

The wood siding that is dark black in appearance is also the result of a charring process, known as yakisugi or shou sugi ban in Japanese. Other types of wood-burned building materials exist too, such as the French-burned and char-wood. All of these result in a blackened finish! But this is not just for aesthetics. The Japanese applied this technique to traditional housing with a procedure of creating the charred surface by combining three planks of wood to form a chimney shaft between them where a flame would run upwards. The wood planks were then splashed with water to remove the flame and cool them quickly.

The resulting burned surfaces of the wood planks actually provides a natural fire-retardant! So there is no need to apply other chemicals or toxins. In addition, the charred surface is insect repellant and water resistant, giving durability and maintenance benefits for using the building material on exteriors as well as interiors. Finally, because most biochar materials are utilized for filtering particulates from air or water, yakisugi gives this benefit to the ambient air too while also adsorbing carbon dioxides. Of course, the traditional burning techniques for creating yakisugi create some carbon emissions, but modern kilns utilize carbon recapture techniques to mitigate this effect.

Yaki means to char, while sugi means cedar in Japanese. So traditional yakisugi methods were applied primarily to cedar wood types. But today, the charring process can be applied to many different species of wood, including cypress which is fast-growing in forests of Japan. The wood that is sourced for these building products should come from sustainable forestry certified practices, ensuring that older lumber (80-100 years of age) is sourced with thin-cutting rather than clear-cutting. Many of the sustainable forest practices also apply afforestation (rather than deforestation) by expanding the range of the forest with new plantings every year.

The charred wood building siding material is a great sustainable substitute to other building sidings that are manufactured as plastic composited with toxin-based chemistry. Maintenance of yakisugi is minimal, but to maintain the same appearance beyond 30-years, repeat coatings of zero-VOC (volatile organic compound) finishes or natural oils. Installation of the siding occurs as the final layer on exterior walls, with a simple wood frame sub-layer to nail the planks into, providing an air-gap between the exterior weatherproofing and the yakisugi planks. The wood should not remain wet for long periods of time, so it does not bode well for extremely humid or consistently rainy climates. Nor should the wood planks touch the ground as moisture could be constantly wicked up by capillary action. The planks also don’t fare too well in super dry or arid climates as a warping of the wood will tend to occur.

Natural weatherization can occur and lends to its own aesthetic known in Japan as wabi sabi, or an appreciation for beauty found in slight decay and deterioration. Ultraviolet rays from the sun, such as those hitting the south-facing wall of a house, can eventually cause the black char to wear away and the wood to turn a reddish-brown shade. North-facing walls of a house, with little exposure to direct sun (in the northern hemisphere) will result in weatherization of the wood turning to a light-grey shade. These subtle changes occur over many years and can be otherwise prevented with more consistent refinishing of protectant oils. Roof eaves and overhangs can also provide an additional layer of protection for the wall siding from harsher weatherization exposures. Most yakisugi exterior siding materials last more than 100-years according to documentation of numerous historic examples across parts of Japan.

If you are planning any exterior siding replacements for your house and want to know the best selection for your location and climate, reach out to AIDA, LLC today for a consultation. You can always find more information and healthy home resources at Aletheia Ida Design and Architecture, LLC (AIDA, LLC) at www.aletheiaida.com.