Life in an old Japanese house Vol.6: The durability of wooden structures and the effects of humidity

Japan is a humid place full of acidic soil making rot and termite damage an ongoing concern for owners of wooden homes. By making structures with brick and mortar like in Europe though these problems would be reduced, with Japan’s high humidity levels mold growth from condensation would be a different headache. Compound this with the ever present risks of earthquakes, and wooden homes were the norm right up to recent times.  

Herein lies the fundamental difference between the concepts of durability in Western masonry structures and Japanese wooden structures. For masonry structures where once built, the structure will last over 100 years, the quality of construction materials and thickness of the walls in a building’s design will directly influence the structure’s durability. Whereas in the case of Japanese structures, no matter how high the quality of wood is implemented, there is no denying the risk of rot and decay from moisture and termites. Therefore homes can be thus maintained by simply replacing any damaged wood. In fact homes built before the 20th century were often constructed with the kumiki method of joining grooved wood together. Such homes can have their wood switched out without even leaving any marks on the surrounding wood provided one possesses the knowledge and skill of kumiki.


Image from the Illustrated Blueprints of Western and Japanese Architecture.  Depicted is the method of constructing a four-way foundation on a pillar with only 4 pieces of wood and no nails or hardware.
A&B: Wooden bar under the floor. C: Hole for the Sleeper. D: Another example of how to fix the post without Sleeper. E: Fixing slit for the Sleeper(大引) and Joist(根太). 

It’s easy to find many old homes that were originally built without indoor plumbing, a bath, or toilet that later had them installed during Japan’s modernization after WWII. It’s also common to see an entrance or guest room added onto the sunny side of the home with plumbing installed on the opposite side. In these darker parts of the home such as under the floorboards, in the plumbing of the bath, kitchen, or toilet, and in the closets, it is particularly easy for air to stagnate making them likely places for moisture to collect and decay.

Considering that patriarchy was ever present in traditional households of the past, the customary decision for male homeowners to place the plumbing and the kitchen on the underlit side of the house was in part motivated by a lack of respect for women. Nowadays, women are more a part of the conversation for home remodeling so it’s more common to see kitchens built on the sunny side of the house. When considering remodeling an old home you reside in, you may also find it’s a good idea to do heavy renovations to the layout.

adf-web-magazine-underlit-northside-of-the house

Doing the washing in the cold underlit northside of the house was certainly miserable for housewives.


When extensions are added onto the side of a home, it was commonplace to build the addition slightly lower than the rest of the home so the lower roof would overlap with the main roof. This meant that the floor was lower to the foundation making it much harder for air to flow sufficiently.  No matter where your kitchen or plumbing is located in the home, it is always ideal to have the floor properly elevated so air can flow sufficiently. After revisions to the Building Standards Act after WWII, homes foundations changed from having independent footing to continuous footing which meant the wide open spaces under the floor became just a tiny air vent. This is why it is important to be aware of having proper airflow in your home and never block or obstruct any vents or put things under the floorboards. Some homes may place moisture absorbent packets to help curb moisture damage but it would be just a drop in the bucket for homes built on a lowland or wetland where moisture is sure to collect quickly. It is more practical to improve air flow and use moisture resistant building materials instead.



Here is a traditional home built on independent footing. You may find boards were put up to block animals entering, but it is better to replace them with wire netting instead.


Here is a vent built into a continuous footing foundation, maintaining sufficient airflow here proves to be challenging.

Now that AC units are an indispensable part of every home, making rooms airtight is ideal for making a comfortable environment. That said, changing the home for this purpose without ensuring proper air flow or proper insulation will shorten the lifespan of your house from damage caused by excess condensation. It is worth repeating that you should bear this in mind when renovating to add proper insulation and air vents to the appropriate places.

As the efficiency of air conditioning equipment and reinforced concrete improved, homes built from reinforced concrete became more common. The concrete used in buildings constructed from post-WWII and throughout the economic bubble mixed in sea sand that contained salt resulting in rust forming on the metal bars. In addition, the steel bars in reinforced concrete are said to last only 50 years that specified by the ministerial ordinance so this is why you should be careful when purchasing old buildings made with reinforced concrete. On the whole, I would say avoid buying homes constructed with reinforced concrete. Even if you find a building that uses properly constructed concrete, though general upkeep is easy, maintenance on the structure is far more challenging than a wooden structure. In fact, there are cases that a whole reinforced concrete structure has to be taken down and rebuilt when just one part of it fails. If you are considering choosing an old home to repair and maintain, then I would say wooden structures are the smarter choice. In addition, modern wooden homes often use cheap and inferior wood in their structure so in fact an older wooden house that uses stronger wood would in fact be a better choice. Wooden structures may need more upkeep than a concrete structure but when properly maintained, they can last longer providing you years of comfortable living.