Shou Sugi Ban.
How long does it last?
How long does it last?
The short answer is it will outlast you and your kids. All the timber species we use meet the New Zealand standards as fit for cladding. With our fire conditioning we improve on that rating.
In Japan many examples can be found that are over 80 years old and are still weathertight. Incredibly, they have never been oiled or stained. In New Zealand, recommend stain every 7 years for a full charred finish which will give that char more strength and longevity.
We are always asked how long does shou sugi ban last, and is it true it can last 80 years without maintenance. The answer is yes it can. The first thing we tell customers is the single most important factor in any cladding having a long life, is good installation.
Below is a little more detail from Japan.
I’ve travelled a lot all over Japan looking at how cladding is fixed, how it performs when very old and how it weathers in different environments. Japan is the birthplace of charred timber cladding and its easy to find many 100 year old examples. When I was last there in 2018 I travelled by motorcycle from Hokkaido to Kyoto to see new and very old examples of yakisugi. Many appeared to be well over 50 years old, and many still in great condition.
But as a kiwi timber professional I am not skilled in old yakisugi, and I needed to find someone who was. William Beleck the General Manager of Nakamoto Forestry is an expert, and the following is what is what he had to say about how long yakisugi will last. - Please note all photos are of very old and unmaintained Yakisugi.
From The GM of Nakamoto Forestry
Before my life as GM at Nakakoto I used to be a remodel carpenter so can age buildings with some accuracy. The question of how long yakisugi will last is a good one, so I decided to spend some time to clarify this 80-year longevity rumour since it is an important topic.
First of all it is difficult to give a blanket longevity statistic for any kind of building material, especially cladding which is affected so dramatically by install spec, maintenance, local environment, and each specific wall’s orientation. Also, how do you define cladding longevity, especially when rot is not a factor? (Correctly installed cladding doesn’t rot.)
Houses are rebuilt on average every 34 years in Japan, every 72 years in North America, and 50 years in New Zealand, so what does it matter if yakisugi lasts 80 years or 120 years without maintenance?
Note we are discussing wood longevity here, and it is important to differentiate between wood and colour longevity. Colour is more dependent on oil stain maintenance.
INSTALLATION EFFECT ON LONGEVITY OF CHARRED TIMBER CLADDING.
Let’s start with installation since this is hands-down the most important factor in cladding longevity. If cladding is not installed correctly–for example not flashed correctly or installed directly over a resin vapour barrier without a cavity –then it can start to rot immediately. Whether it’s cement board, cedar, or yakisugi cypress, if the cladding is not allowed to dry out quickly then it is going to rot.
Cement board that stays wet will start to delaminate after about 6 months. Any kind of softwood will start to rot within a couple of years if it stays wet. So the better the installation, the longer the cladding will last. This is not the longevity limiting factor that I’ve seen in Japan, except on structures where the bottom of the wall is in contact with a stone or cement foundation. Wood wicks water from masonry and direct contact will cause wood to rot.
Age estimate 80 years old; note rot from direct masonry contact, also colour difference between high-UV load center of wall and silvering at the bottom from moisture.
MAINTENANCE EFFECTS ON CHARRED CLADDING.
Wood is degraded over time from UV radiation, the freeze-thaw cycle, abrasive coastal weather, and if it’s not allowed to dry out quickly enough. Oil stains or paint slow down the weathering process, so regular re-oiling will slow down wood degradation over time. Yakisugi is never painted because it is more beautiful stained than painted. Oil stains are hydrophobic causing water to bead and roll off, and pigment in the oil acts as a UV blocker. UV radiation breaks down the wood fibers and then wind and rain wash the degraded wood off of the surface.
Yakisugi is rarely maintained in Japan, and what I’ve seen is that the yakisugi boards get thinner and thinner over the decades from UV degradation. Nails will get more proud of the surface as the wood surface erodes.
Once the boards get too thin, the boards start to split. This takes 80~150 years depending on plank thickness and wall orientation.
Cladding in New Zealand starts at 18.5mm thick, in Japan it is standard 10~15mm thick, and a 10mm plank installed facing south or southwest (North or North West in NZ) orientation will wear through and start to split, exposing the substrate, in about 80 years. So in Japan UV degradation is the defining factor in yakisugi longevity since they traditionally rarely do re-oiling maintenance.
Age estimate 60 years; note uncoated traditional cut nails, ferrous streaking, nails backing out, wood erosion making the nails proud
Age estimate 80 years; note wood thickness erosion and checking, masonry contact, also 30~40 year old Suyaki patches
Age estimate 80-100 years; note intact soot layer where protected from rain, ferrous streaking, 4 nails per board, Suyaki erodes to a Gendai appearance over time, wall is likely north-facing.(South face NZ)
ENVIRONMENT EFFECTS ON LONGEVITY
In terms of geographic location, in our experience, coastal marine and humid subtropical climates are the most challenging in terms of wood cladding longevity. Coastal climates are abrasive with salty air so wear through wood more quickly, and humid climates encourage the growth of fungi in the wood that can cause rot.
Yakisugi lasts longer than un-heat-treated wood in these applications since the surface is case-hardened for abrasion-resistance, and also the cellulose/hemicellulose that fungi grow on is burned off. Arid or cold climates cause wood to dimensionally move (cupping especially) and change colour , but they do not cause as much abrasion or rot as coastal or humid climates. This is why yakisugi is more common along the southern coast in Japan than inland or up north.
Finally there is specific site or wall orientation. What I’ve seen in Japan and North America is that wood will weather differently depending on which direction the wall is facing. In general east and north facing walls (East and South in New Zealand) will evenly bleach out until they are silver in colour , then they will remain an even silver.
South and west facing orientation (North and West for New Zealand) will weather unevenly. The top of the wall is protected from sun and rain by the overhang so will remain the original colour . The center of the wall will turn wood colour from high UV and since it dries out quickly after rain.
Then the bottom of the wall will silver out similar to the east and north (east and south NZ) elevations since it remains wet longer. Keep in mind this only happens if the cladding is not re-oiled.
Age estimate 15 years; note silvering left side from daily exposure to an adjacent river’s morning dew, right side warm wood colour from high UV load.
In conclusion, the 80-year estimate would be from : Japanese standard 10mm thick boards that started out as our Suyaki full char surface (ie Not brushed), were installed correctly, were never oiled or re-oiled, were installed on a south or west-facing (North or West NZ) orientation, and near the coast.
However, if the cladding starts out thicker (our New Zealand standard is 18.5mm this is because yield drops off for any thicker than that), is installed correctly is finished with an oil stain, and re-oiled periodically, it will last even longer. How long is the unknown for New Zealand conditions? But we would hazard a guess that your grandkids will not need worry.