Life in an old Japanese house Vol.10: Japanese Houses Walls part. 1
As you may know, buildings with masonry walls constructed of brick and stone support the structure and thus destroying a wall directly impacts the building. However, Japanese wooden homes are built on a frame of pillars and beams and thus if the frame is intact, destroying a wall doesn’t mean the building is ruined.
This is why provided the pillars and beams aren’t touched, it is relatively simple to knock out the walls and remodel the layout of a Japanese home as you please. On the other hand, although walls can be added to further divide up the space of a masonry structure, it is rather difficult to greatly change the layout of a masonry structure since consideration for retaining the load-bearing walls is critical. This flexibility that allows the layout to be freely changed, unique to framing structures, is what I believe led to Japanese homes being constructed on a structural frame.
This is also one key reason that renovating old Japanese homes is seeing a surge in popularity nowadays.
While modern Japanese wooden homes have walls made of plywood or drywall, most walls in old homes were made of dirt.
Traditional dirt walls are constructed by the wattle and daub method wherein crosspieces of bamboo or thin pieces of wood are interlaced between pillars and held in place by rope to form a lath which is a backing material used to hold the dirt. Finally fiber including straw and paper are mixed into the dirt and this plaster like mixture is applied to the wall. Since it takes a long time for the dirt to dry, making dirt walls with this traditional construction process can take anywhere from a few months to up to a half a year! First a rough first coat of dirt is applied to the lath and left to dry for a few weeks or even months, then an intermediary coat is applied and also left to dry for weeks or months and then finally a top coating of Japanese plaster is typically applied to finish the wall. The know-how of properly making these traditional walls requires the expertise of a professional plasterer which means they are costly to build. Old buildings such as tea houses and registered cultural properties will contract a professional plasterer to repair their walls but a new building built with traditional dirt walls is almost unheard of.
Homes built around WWII for the most part have their dirt walls still intact, but when these homes are renovated new walls are hardly built with dirt and instead plywood or drywall is employed. Though it is attractive to use dirt since it is a renewable and sustainable material, because dirt used in walls if left to soak in water will eventually turn to mud. Plus it is true the bamboo and wood used for the lath are easily acquired, however, due to the time and expertise required, few would elect to build these walls nowadays.
Earthquake resistance is an ongoing concern so there are many instances of dirt walls being converted into load-bearing walls by tearing down the wall and installing cross-bracing with structural plywood. This isn’t to say that old homes have no earthquake resistance since dirt walls can absorb quakes and tremors plus the cross pieces help stabilize the home from collapse. However, the home can still collapse if the overall balance of the structure isn’t sufficient. Suppose a two-story home were to have more walls on the second floor than the first, then the weight of the dirt walls would therefore become a liability increasing the risk of collapse. However, if the number of walls were even then a traditional home wouldn’t collapse that easily.
I myself have on numerous occasions pulled down homes and cellars without heavy machinery just as people did in the past, trying to pull down an old home with its dirt walls still intact won’t move an inch. If the walls were knocked down but the cross-pieces were still intact then the home would greatly sway. Finally, if the cross-pieces were severed then with the help of a few people the home will easily collapse.
I had known that when there were no fire trucks during the Edo era (1603-1868) that the homes surrounding a fire were pulled down in order to prevent a fire further spreading but I was rather surprised when I actually did it myself to see how easy a home comes down if the walls and cross-pieces are first removed.
Though buildings built on a frame are structurally reliant on their pillars and beams, when faced with the force of an earthquake or heavy winds, it is easy to see these non-load bearing dirt walls also serve a purpose.
Bear in mind when considering major renovations to a home, that though anyone can easily knock down dirt walls, when considering adding cross-bracing and structural plywood to improve a home’s earthquake resistance it is of the utmost importance to consider a home’s overall structural balance according to the location of its walls and other kinds of reinforcement and how it will impact the overall strength of the home.