|Random street in London, the UK is particularly fond of townhouses that they called "terraced house", nearly 70% of the population lives in attached homes
Even though the Japanese have plenty of high-density areas full of single-family houses, these areas almost always steer clear from townouses. They do have a few of them, mostly in older areas, and some developers build apartments in townhouse format rather than in the typical format.
|Apartment building built in a townhouse format in Sendai
|This is an image from Osaka
The basic logic of the townhouseThere is a simple logic behind townhouses and attached buildings in urban areas. The biggest attraction point of single-family housing over multi-family is the promise of one's own personal yards, access to a small portion of land that is shared with no one. The back yard is the single most important selling point of single-family housing. The front yard is still important in preserving privacy and offering a customizable façade for the house, so that's another big selling point.
If we look at a single-family house schema, we'd get this:
|Basic schematic representation of a single-family house
A typical house tends to be wide but shallow, a way to increase density is thus to rotate it, so the shorter side is facing the street.
|This achieves nearly twice the density of the house above
For urbanists focused on "feeling" or on the look of areas, the presence of buildings wall-to-wall reinforce a feeling of enclosure, of unbroken lines of buildings forming walls for the street, which they frequently seek as it evokes European cities.
The problem with townhousesTownhouses seem to make a lot of sense, but they have one big flaw: the lack of exterior walls on which windows can be installed.
It is a factor that may be often forgotten, but windows are crucial for proper living quarters. It's not just about the view, but about air flow and natural illumination. In some jurisdictions, it is downright illegal to have a bedroom without a window to the outside, and even when it is legal, people avoid them like the plague, with good reason. Even a window opening on a wall within a few feet of it is considered much more desirable than no window at all.
Of course, in the past, before efficient house heating, building houses side-to-side reduced heat loss in winter and made it easier to keep living areas warm. However, today we no longer have problems with heating, so that advantage is much less significant than in the past.
If you look at the picture of the Japanese homes, you can notice windows on the side walls, even with the tiny amount of space available. I also have seen such windows in Tokyo Hotels, for example:
|Photo from the inside of a Tokyo hotel room
|With the window opened
|A picture taken right out of the window, showing what space there is between the two walls
|The blue bars indicate where windows can be installed, the red bars show where they can't
This also means that the detached house can have more bedrooms for a same floor area as bedrooms need to be located next to an exterior wall with windows.
There is a major difference between Japan and North America that may explain partly why the Japanese favor small detached homes over townhouses. In North America, parallel streets are often separated by 60 meters (200 ft) or more, as a result, lots tend to be very deep. In that context, reducing width is essential to get some density. Meanwhile, Japanese streets are built much more tightly together, separated only by 35 or 40 meters (120 to 130 feet), so the Japanese don't need to build narrow townhouses to get high density in single-family areas, the lots can be wider because they are a lot shallower:
|Left: townhouses in a typical North American street grid, right: small detached homes in a Japanese street grid, both images have the same density
|Left: a random neighborhood of Minneapolis, right: a recent random single-family area in the small city of Sano in Japan, yes, the images are to scale
This is true for townhouses, but also for apartments. Apartments built in depth with little frontage will also struggle to find ways to have many bedrooms because of the lack of windows. This is why Montréal, which housing stock is primarily made up of low-rise apartment buildings built side-to-side, struggles to have more than 2 bedrooms per unit in that type of housing, as it is very hard to design an apartment that has three bedrooms with a townhouse-style floor space with windows only on the narrow front and back.
In the past, people have found a way to go around this problem by using a fat, reversed L- or T- shape.
|Apartments with a T-shape in Montréal, separating the walls in the back of the buildings to create more exterior walls and opportunities for windows
|Another example in Montréal, more of an reversed L-shape here
|Now an American example, Philadelphia, with its traditional rowhouses with L-shapes
A compromise: the semi-detachedThe semi-detached is a compromise between the attached buildings and detached buildings. With just one shared wall, the semi-detached can still have plenty of windows while reducing the lateral buffers between buildings. This can provide for greater density while maintaining some of the attraction of detached houses, it can also provide a way to deal with the deep North American lots by allowing for the construction of very deep houses or apartments, increasing building coverage to the lot that would hardly be possible in an attached context, and increasing the possibility of building more bedrooms per unit.
|Semi-detached houses in the UK, where the style is quite common in more suburban areas
|Semi-detached houses in Boucherville, double the density of typical bungalows, but each unit is still wide enough that it doesn't necessarily require side windows
|Typical condos found around Montréal, which are basically two semi-detached triplexes built in one building, providing big (1000+ square feet), affordable housing options in suburbs
ConclusionIf attached buildings and townhouses represent a very efficient spatial organization and are typically associated with urban areas, especially in Europe, they are not necessarily required for density and good urbanism. Though they are also well adapted to the typical deep North American lot, townhouses' lesser access to air and light may be a turn off for a generation born in suburbia who may crave more density but who still remains attached to a detached lifestyle (pun not intended). This may also explain why I personally find residential areas in Japanese cities more attractive than European cities, due to better aeration and light access, as I was raised in a North American suburb and am more used to the more open, less enclosed feel of them.
Oh, and finally, a last point about why the Japanese skirt around attached buildings: remember that the Japanese think that buildings have a limited life expectancy, that they should be torn down and replaced every few decades, whereas the European/North American approach is to consider buildings to be built to last at least a few lifetimes. The Japanese approach of tearing down and rebuilding is much easier to do with detached buildings than with attached buildings where tearing down a building without affecting the ones on either side with which it shares walls and which belong to different owners can require a lot of attention and care.