Recently I was asked by an Architect in Wellington how long will the char layer last on the timber. I told him what I tell everyone, I have seen many 30-40 year old examples in Japan that still hold their full char and this is without the protective oils we use.
He replied, but what about New Zealand's unique climate and weather conditions? I had to admit the effect of this on our charred timber was an unknown to me, but I thought we must have similar weather patterns.
I decided to do some research in Japan's weather and climate in direct comparison to New Zealand's. What I found surprised me, with Japan being a notability wetter country with more extreme cold and heat, New Zealand had a slightly higher wind speed, and both countries have the same number of rain days per year.
Japan VS New Zealand Land features
Japan is made up of 5 main Islands with the largest being Honshu, this is where Tokyo, Hiroshima and Kyoto are all found. Honshu is surprisingly similar to New Zealand in size and position. I decided to look at this island for the comparison, you can see in the images below that it's very similar to NZ.
Land Mass. Land Area: Length
Honshu - Japan 227,960 1200km
New Zealand 268,021 1600km
Honshu - Japan 230km 3754m (Mt Cook)
New Zealand 450km 3776m (Mt Fuji)
Map Overlay to scale of Japan and New Zealand.
I was surprised at just how physically similar New Zealand is to Honshu Japan, 22 meters difference in the tallest point!
This was a very encouraging find, given both countries are long thin Island masses sitting in the middle of a large ocean, I was really interested to see how our weather and climates compared. But first I wanted to see if we sat in similar proximity to the polar caps and equator. I have tried to use comparable major population centres that sit at similar latitudes.
Distance to Polar cap
New Zealand 5420.92 km (Wellington 41°S)
Honshu 5484.74km (Aomori 41°N)
3916.79 (Kerikeri 35° S)
3906.52 (Kyoto 35°N)
Another significant box ticked, now based on location, size, length and width we can safely say New Zealand and Japan are uncannily as close as two countries can ever be. I realised that Japan's major difference is the massive land mass to the north-west, and this would have effects on its weather. With the countries being comparable land masses to understand if New Zealand has more adverse weather, all I needed was a simple weather data comparison.
12 month Rainfall: mm
Kerikeri 1049 Kyoto 1677
Auckland 1114 Kitaibaraki 1435
Wellington 1249 Aomori 1353
Queenstown 741 Tokyo 1500
Average number of Rain Days
NZ wins by a hair.
New Zealand 117.3 days
Honshu Japan 115.7 days
12 month average Wind Speed: KM/H
New Zealand wins
Kerikeri 22 Kyoto 17.4
Auckland 20 Kitaibaraki 20.2
Wellington 29 Aomori 23.8
Queenstown 16.1 Tokyo 10.1
12 month temperature Range:low/high
NZ ` Japan
Kerikeri 9°/23° Kyoto 1°/33°
Auckland 7°/24° Kitaibaraki -2°/27°
Wellington 7°/21° Aomori -5°/28°
Queenstown -1°/22° Tokyo 2°/31°
One factor not captured here was the humidity, which is higher on average by 10% in New Zealand. Humidity will have an effect on timber but not on char, which is why I have not included the data.
In conclusion, shou sugi ban charred timber should last as long in New Zealand as it does in Japan, in fact longer as we apply oil stain every 7 years. New Zealand and Japan are highly comparable in climate and weather, you might even say Japan has a harsher climate with its higher rainfall and more extreme temperatures.