When you live in a semi-tropical climate with fiercely hot and humid summers, near the ocean with its constant salt loaded winds, and you can only build with wood, how do you build walls with only natural materials to last a hundred years or more without maintenance...?

For the people who lived around the Seto Inland Sea in Japan, the choice was the shousugiban (better known as yakisugiita, 焼杉板): thin planks of cedar wood deeply charred on the outside.

The charred wood is salt water resistant and extremely resistant to heat, protecting the house interior from the summer sun and at the same time keeping bugs and insects out. I've heard of walls lasting over 100 years without any maintenance at all. It's also cheap, easy to make.

These days it is mass produced in kilns, heated to 1300 degrees, but for smaller building projects it is still hand made: boards of cedar tied in triangles and held over a fire a few minutes until fully charred, then extinguished with cold water.

The charred surface is also very fire resistant. In a spontaneous test, untreated cedar boards caught fire after about a minute when held to a blowtorch. The charred cedar boards lasted over ten minutes before the tester ran out of patience. For this reason it is common on kura.

Recently shousugiban (simply another way of reading the characters for yakisugiita) has become popular again with modern architecture, and you can find it even in central Tokyo. It is a low cost non-toxic, easy to instal material. It's only drawback is that it is sooty to touch.

But of course it looks best in traditional Japanese architecture, and especially where it was first implemented, near the ocean, in fishing villages and boathouses.

For almost every human need and predicament, some sort of natural device, sustainable construction method or just material trick, has been invented by our ancestors. By building with nature (fire, water, wood, earth), we can become better stewards of our environment.