Land plot size is so small and expensive, that Japanese houses have to be built on a very tight leash, with thin walls (downside: no acoustic insulation, you can hear everything your neighbors do or say, and poor thermal insulation, which has to be compensated by overusing the air conditioner) and poor living conditions.
How does this translate over to building a house though. Debito once wrote an article about his adventures in building his own house, and per Debito-style, went on at length about the retarded Japanese building codes and what not. But I take what Debito says with a micron grain of salt.
Is it really because of building codes that walls have to be so thin? Is it also because of building code that all Japanese homes and buildings have to use the same kind of stone roof tiling?
well, to put things into context, I explained that the building code (and historical events) was the main reason why Japanese houses would be considered illegal in other countries (of course, the differences in law between countries are big).
It's not a shocking thing at all. what is considered legal in a country can be illegal in another, etc etc etc...
I did not read debito's rants, but I have heard japanese architecture teachers claim more than one that the building laws were inadequate and out of step with the modern times.
To clarify things, there is a system a work here, composed of many things.
There is a complex building code with many articles (and some internal conflicts);
There is a historical usage of land space, which caused it to broken up in ever smaller pieces, and it is difficult to "defragment" them in the name of good urbanism;
There is a manufacturing and construction industry, which has deep roots, connections with politicians and promotes standardized manufacturing methods;
These construction companies hire engineers or young architects to create "custom-made" cheap prefabricated solutions, where the client just chooses a color or some basic components and the rest of the house is done for them, at a lower cost than paying an independent architect (who can guarantee a more unique look and solution);
There is a situation where land prices are high;
All of these factors together, generate the majority of the housing panorama in Japan. The laws do not force houses to have thin walls, but the shortage of land area, combined with the minimum room sizes dictated by building law, combined with greedy promoters who want to obtain as much return per square meter by putting as much rooms as possible in a short space, combined with manufacturing companies that want to promote cheap construction solutions do.
roof tiles are a consequence of standardized production processes promoted by companies. On the one hand, land is costly, and after buying the land a family will have to face the choice between a construction company that builds a cheap fabricated house (you simply have to choose from a catalog), or an independent architecture office that cannot compete with those companies in terms of price, and will produce inevitably a costlier solution.
Inevitably, families will go for the cheaper solution, and the japanese desire to "blend in with the crowd" also plays a part in this.
So, there are many things at work at the same time.
EDIT: Often, architects are given a plot of land that is just 2 meters wide per 5 meters in length, and they have to design a house there. just to comply with the building code that gives a minimum corridor width of a meter or so, every milimeter counts, so walls will have to be thinner. But it is also in the middle of such restrictions that the Japanese can be really creative. They have come up many times with elegant solutions that do not solve every problem, but can accomplish a myriad of things.