Written by: Donald Peckover
Question: I have heard about Shou-Sugi Ban, but what the heck is it?
Shou-Sugi Ban is a Japanese cladding technique that preserves wood (making it resistant to fire, vermin, and decay) by first charring it, then cooling it, cleaning it, and finishing it with natural oil. We have used this technique on our very own METHOD.TO test shed, charring the wood ourselves; but for other projects in Toronto we have left the fun to the professionals.
Wood cladding remains a popular choice for many projects, by many people. It is a natural product from a renewable source – forests are abundant in Canada, and with the prevalence of the Mountain Pine Beetle in BC threatening and terrorizing our forests, we simply cannot cut down trees fast enough. This seems like a bad thing, but in fact we are saving the forests from decay and replanting at a faster rate with more diverse, resilient species for the future. This may sound counter-intuitive, by cutting down trees we are sequestering the carbon and greatly reducing carbon released into the atmosphere through decay and forest fire.
Wood cladding inherently requires maintenance. Factory coatings and sealants can make wood cladding more durable, but these chemical finishes are often harmful to the environment. Shou-Sugi Ban uses a lot of elbow grease and natural finishes to create a durable, natural cladding option from a renewable source.
Charring the wood creates a layer of carbon on the exterior face of the wood. This carbon is resistant to further fire damage, making the cladding much more safe in dense urban settings (where fires can leap across property lines) or in rural forested areas (where forest fires can jump from the forest to the home). Further, the layer of carbon provides a robust protection layer against vermin and pest infiltration – termites, ants, and mice. And lastly, charring the wood and sealing with natural oil provides a durable and sophisticated finish to the wood which can last for years with minimal maintenance.
For cladding applications cedar is typically used. “Clear” cedar without knots is more expensive but has a smooth, uniform appearance. Lower grades of cladding with knots add more character and variation to the finish, and are what SUSTAINABLE.TO likes to use as an attractive, varied, and cost-effective alternative.
Tongue-and-groove cladding is best – wood expands and contracts with heat and moisture, and when fully charred the tongues-and-grooves present a continuous charred surface regardless of expansion and contraction.
Other types of cladding are also used, such as board-and-batten or shiplap, but extra care is required during installation.
The process of charring the wood should be carried our prior to installation of the boards on the house or structure, for a few key reasons: it is easier to perform the process on the ground rather than on a ladder, and it reduces the overall fire risk. Here we stacked the cladding on pieces of non-combustible ROXUL insulation.
Step One involves charring the surface of the wood. A roofing membrane torch can be used for this step, and can be rented from Home Depot. Make sure your “tongues” are exposed in order to achieve full char coverage – we didn’t when we did Shou-Sugi Ban for our METHOD.TO test shed and had to go back for touch-ups prior to installation.
Step Two involves cooling down the wood, either by dunking into a long trough of water or pouring a bucket of water over the wood. This stops the burning process, lowers the temperature of the wood and makes for safer storage.
Step Three is cleaning, and may be considered an optional step by some, depending upon the type of finish you desire. By leaving the char uncleaned it imparts a rough “alligator skin” finish. This type of finish is typically darker and blacker then cleaned finishes. Cleaning with a stiff wire brush – brushing with the grain – smoothens and shines the surface and can create a silvery glow depending upon lighting. Cleaning the wood creates a warmer, lighter surface which picks up on the rich red undertones of the cedar without any change to the durability to fire, vermin, and decay.
On one recent project we lightly “toasted” the wood, leaving much of the natural wood grain exposed. Finished with a natural oil this achieves a similar low-maintenance cladding, but with slightly less protection than is offered by a full layer of char.
The last and most important step is the finishing. We use a natural tung oil, which can be found at Home Depot or at your local paint store. The natural finish coats the wood and protects it for the long term as well as during construction. The oil keeps the char from splintering and turning to dust during cutting, drilling, and installation – much safer for the workers. The oil also prevents the char from rubbing off, maintaining a smooth finish over time and ensuring your clothes and fingertips remain clean.
“... and why should I care?”
While Shou-Sugi Ban siding has a lot of “sweat equity” built into it, the longevity and low maintenance of the cladding material over time means fewer costs and headaches down the road. Natural resistance to fire, vermin, and decay means lower need for replacement. Natural oil finishes don’t need yearly re-applications. Overall, Shou-Sugi Ban is one of SUSTAINABLE.TO Architecture + Building’s favourite materials, and we would be happy to speak with you about installing it on your home or structure.