The Top 10 Myths About Shou Sugi Ban Charred Wood Siding

Over the years we’ve seen a lot of mixed information circling the web surrounding what shou sugi ban is, how it is used, and wood siding in general. As industry leader since the 1970’s we feel it’s our responsibility to set the record straight. So here are the top 10 myths we’ve come across and the truth about each one:

Myth #1 Cost: You get what you pay for -or- Shou sugi ban is expensive

While both are true at the extremes, shou sugi ban is a vernacular material maximizing millwork tradecraft, so making it is more knowledge-based than expense-based. That means it should have good value compared to other cladding options and a vendor’s high cost might more reflect custom millwork, high overhead, or pricing strategy.  The Japanese heat treatment process does not add that much production cost to the wood product, and shou sugi ban should not be much more expensive, if at all, compared to other stain-grade wood siding options.  Also when long term durability and little need for maintenance is taken into account, long term cost performance is fantastic. Since this is a vernacular material, affordability has always been associated with shou sugi ban in Japan.

 

 

Myth #2 – Sustainability: Regional wood has a lower carbon footprint and costs less

The modern supply chain is varied and driven by economics.  Lumber is sold on an international market and can be efficiently transported.  Finished products are more efficient to ship than raw materials. Ocean freight has a much lower carbon footprint than regional trucking or even transcontinental rail freight in terms of pound moved per mile (ratio is ocean = 1, trucking = 7.1, rail = 4.9).  Case by case local or non-local materials can have lower cost or a lower carbon footprint.  Assuming regional materials check both of these boxes is a false assumption and allows “greenwash”.

 

Myth #3Species: Many species work for making shou sugi ban

Any species can be burned with varying degrees of success and appearance. But for several reasons only cypress (often colloquially called cedar) is used exclusively for shou sugi ban in Japan. Since shou sugi ban is made to be used as exterior siding, it should be dimensionally stable throughout all seasons, last a long time in various climates, have good cost performance, and be great looking.

The following characteristics are why we find certain sub-species within the cypress genus have best performance for shou sugi ban exterior siding:

  • Light, porous softwood works best due to deep heat treatment penetration, dimensional stability, and a fast dry time in wet weather
  • Hard or dense wood species often twist, cup, and split over the long term when burned at high temperature and then exposed to exterior weather
  • Thick latewood growth rings turn into a solid, longer-lasting protective soot layer after burning
  • Tannin, mineral content, and essential oils (not resin) are natural biocides that prevent rot and repel insects
  • Good grain pattern and color variation are considered beautiful when brushed or after decades of weathering

 

Myth #4 – Level of Char: Different shou sugi ban finishes are made by burning to a shallow or deep char

All shou sugi ban is burned deeply to heat treat the wood, then after burning different surface treatments can be used to achieve varied appearance.  The sooty, textured surface can be left alone for protection and character (Suyaki), it can be brushed lightly for a smooth and more refined appearance (Gendai), or it can be wire-brushed to show more of the grain texture and color (Pika-Pika).

Cosmetic “shallow” or “light” burning is similar to aburi, a traditional Japanese wood darkening technique done with a torch on furniture or interior millwork.  This carbonizes the less dense earlywood growth rings only, not the dense latewood. “Deep” shou sugi ban heat treatment followed by wire brushing leaves latewood growth rings carbonized and black, and the blonde and red earlywood growth rings can be exposed by brushing off the soft soot.  This is our Pika-Pika product. If you know what to look for it is easy to tell the difference between shou sugi ban and “faux” sugi ban (ie aburi labelled shou sugi ban) since the striped grain patterns are negative images of each other. It is confusing and counterproductive to use the words “shallow” or “light” as burning options since that is a faux finish for interior applications, not for heat treated exterior shou sugi ban.

Myth #5 – T&G for Exterior: Tongue & groove is necessary for vertical applications since it keeps water out best, and should be blind nailed for best appearance

Exterior siding is meant to shed water and protect the vapour barrier from UV degradation, not to be waterproof.  Water will always get behind siding and dry time equates to siding longevity, so it is critical that the cladding weeps and dries quickly.  T&G profiles create more water tension at the joint so weep and dry more slowly than shiplap or square planks. T&G was not used for exterior siding until the post-WWII construction boom targeted a low price point and traditional millwork know-how was left by the wayside.  Millwork and heat treatment correctly executed for shou sugi ban will produce a dimensionally stable material, so a locking-type T&G pattern is not necessary. Additionally, the square edges on T&G (or channel lap) will melt if thoroughly burnt and wavy parallel lines simply do not look good.

Blind nailing is also not recommended for exterior wood applications since hidden fasteners cannot be tightened during future maintenance.  The wood will always move over time due to moisture fluctuation and latent instability in the planks.  Face-nailed siding will move less and look better over time since headed fasteners have higher strength and can be easily tightened up periodically with a hammer. Also, due to the high-temperature heat treatment process shou sugi ban is by nature a thin-stock material too thin for hidden fasteners.

Myth #6 – Installation Cost:  Shou sugi ban must be installed by carpenters that have experience with it, and so labor cost will be high

Shou sugi ban is simply wood siding installed with the same carpentry skillset as any other wood siding.  Unbrushed shou sugi ban will slow the installers down since it is delicate and must be handled carefully, but brushed shou sugi ban will actually install faster than most other wood siding options.  This is due to shiplap or square edge boards laying out with less effort than tongue and groove, and since the specific millwork and heat treatment process makes the boards straighter than most kiln dried lumber.  It is best to work with a known conscientious contractor instead of searching for someone that has experience installing shou sugi ban.

Myth #7 – Underlayment: Mesh/drain wrap is an acceptable underlayment instead of furring strips

This myth is related to all siding and not only shou sugi ban.  Mesh or drain wraps can allow enough air flow between the siding and water-resistant barrier, but they do not offer a rigid structure under the siding.  Therefore they will not keep the siding in a flat plane as a standalone underlayment. Mesh can be used for venting under horizontal rigid furring when the siding is installed vertically. But to keep the wall plane flat over the long term the siding planks must be held between fasteners acting as clamps and a rigid furring bed acting as a flat anvil.

Myth #8 – Durability and Color Longevity: Shou Sugi Ban will stay black without maintenance and will last up to 80 years

Unbrushed shou sugi ban will remain black for about 50 years due to the carbonized soot layer, but if the soot is brushed off during manufacture it will be brown and weather in color just like any other stain grade wood siding. As a basic premise shou sugi ban is designed not to ever need an oil finish.  But to keep it a black, brown, or gray color permanently, an oil finish must be reapplied as maintenance every several years just like any other wood siding.

Shou sugi ban will last at least 80~120 years without maintenance and even longer if re-oiled. The durability limitation is that ultraviolet radiation will degrade the surface wood fibers over time and the planks will erode thinner and thinner.  Eventually the siding splits out and falls apart.  Re-oiling maintenance will slow down the weathering process since pigments in the oil offer UV protection and the oil moisturizes the wood.  When the wood reaches its lifespan it is simply replaced.

Myth #9 – Dimensions:  Burning wood is called shou sugi ban and is done by torch on all kinds of species, dimensions, and profiles

There are many wood heat treatment technologies worldwide and shou sugi ban is only one of them.  Shou sugi ban is deeply heat-treated thin-stock planks used primarily for exterior siding. Aburi is a surface burning treatment done by torch to many species or dimensions such as furniture or beams for a darker appearance.  Thermally modified wood by the Finnish low temperature process penetrates more deeply into the wood and can be used on thick-stock for improved durability in exterior applications.  Carbonization by the Chinese process is a high-temperature, hardening process used mainly for flooring. Etcetera.

Shou sugi ban siding is made to last as long as possible under challenging exterior conditions and therefore it is a form-follows-function material. For optimal durability, stability, and fire-resistance performance, certain cypress sub-species are put through a specific millwork and high-temperature manufacturing process.  A torch does not have the necessary BTU energy needed to burn off enough hemi-cellulose in the wood for proper shou sugi ban heat treatment.  A traditional triangular or quadrangular flue, or modern hotbox method, is necessary to apply enough energy to the wood for thorough treatment.  Only thin plank dimensions will stay straight through the hot process due to moisture content fluctuation.  Additionally, the manufacturing process will melt both edges of tongue & groove, fineline, or channel lap profiles, and therefore only shiplap and square edge plank profiles are used to make shou sugi ban.

Myth #10 – SSB vs YS: Charred Japanese siding is called “shou sugi ban”

It is actually called “yakisugi” and the word “shou sugi ban” doesn’t even exist in Japanese.  The term “shou sugi ban” originates around the year 2000 and is a Westerner’s misreading of the Japanese written word “yakisugi”.  People are using the term since either they don’t know better or they are forced to due to keyword metrics!

Leave a Reply

Your email address will not be published.

error: Alert: Content is protected !!