Monday, April 20, 2015

Attached or detached: townhouses and density

One of the big differences that is immediately obvious to anyone visiting Japan is the almost total absence of what is a clear favorite of European and American planners and urbanists: the townhouse. This form of high-density family housing where houses' lateral exterior walls are joined is clearly beloved by a lot of them.

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
The presence of these buildings built wall-to-wall is common to almost all European cities, it is typical of European classical urbanism.

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
But in most cases, the Japanese avoid shared walls at almost any cost, even in areas where it would seem to make a lot of sense:
This is an image from Osaka
These houses have been built at the same time, probably by the same developer (traditionally, the Japanese built their own homes, but in recent years, developers have taken to building entire neighborhoods of single-family houses and selling them), yet despite their proximity, they are not attached, with the smallest of space between each of their exterior walls.

The basic logic of the townhouse

There 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
Now, considering in general the depth of the plot is imposed by the street network and that there is only one household on that plot of land (let's ignore accessory units here), then the only way to achieve higher densities is to play with width, to make the plot narrower.

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
But people can look at this and say: "The back yard has value to the owner, the front yard also... but what about the pieces of land on the side of the building? They are too narrow and small to be of any use, they're not really visible from the street and they don't really help much for privacy". So a seemingly obvious solution is to simply get rid of them, just build homes wall-to-wall.

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 townhouses

Townhouses 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
So, visually let's compare a small detached house with a townhouse of the same size:
The blue bars indicate where windows can be installed, the red bars show where they can't
In this case, supposing a 7m x 7m (23ft x 23 feet) detached house with a 5m x 10m (17 ft x 33 ft) townhouse, the detached house has 28 linear meters of walls per story that can be equipped with windows, of which 14 meters are the front and back, with better air flow and light. The townhouse on the other hand has only 10 linear meters of walls per story that can be equipped with windows.

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
The result of this effect is that it is a very clashing experience to live in a detached home and in a townhouse. The lack of windows on the townhouse can be downright claustrophobic for one used to living in a detached house, like the younger generation is.

A compromise: the semi-detached

The 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
A multi-family type of semi-detached, each floor has two units built in depth with windows mostly on the side of the building, as a result on a 30m-deep lot (100-ft), the buildings are 15-m deep (50-ft) and the apartments manage to be just 5m-wide (17-feet) yet have 2 bedrooms each, which would be impossible in an "attached" situation without making one bedroom just 2m-wide or less (around 6 feet)
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


If 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.


  1. Your examples leave something out: with 200ft spacing between streets, or 100ft lot depth, you can't really have a lot smaller than about 2000sf, with 20ft wide spacing. With 100ft spacing and 50ft depth, you can easily have a 1000sf lot, and indeed houses in urban areas are often on 500-600sf lots.

    Japan has a long tradition of rebuilding from simple necessity. Hurricanes, earthquake, fire, war, flood and debris flows, and volcanic eruptions affect virtually every urban area large and small, so you often don't get more than 40 years out of a building even if you would like to.

    1. Indeed, there is a limit to how narrow you can make a house before it becomes infernal to live in, you can get greater densities by shorter street spacing (or by building a house in front and another in back). But there are plenty of rowhouses in the UK that are 15 feet wide only, so it's a bit smaller than what you said.
      For example:

      The Japanese do have a history of losing entire cities to fires, earthquakes or other disasters, which may have shaped their mentality around houses' life expectancy. Going to history museums in Japan, it's funny how for almost every building, there is always a mention "it was destroyed in a fire in 17XX and 18XX, but rebuilt each time".

    2. Hanoi has tube houses that are typically 10 ft wide but probably developed world residents/Westerners wouldn't put up with 10x80 ft apartments.

      15ft wide homes might still be ok with 7ft wide bedrooms. A 15x40 ft building footprint could be workable and it's pretty close to the dimensions of the townhouse I grew up in which still had windows for each room. It was technically 19x30ft I think, but you probably could have reconfigured it to work with 15x40ft by having more rectangular (rather than square) rooms.

      But yeah, if you have shallow lots, you can make them wider and have row houses that have relatively high densities and good lighting.

  2. I definitely think this is more of an European thing than American. When my cousins from Europe saw all the close packed detached SFHs in Toronto's suburbs, they didn't understand why not just have row houses instead.

    I think when there's less than about 5ft of separation there aren't any windows on the side in Toronto, although I'm not sure if that's by choice or regulations.

    I think a lot of it is a status thing. North Americans see the detached single family home as a status symbol, row houses not so much. Many of the new infill townhouses in Houston are (barely) detached. There's also fire concerns, so Chicago has small apartment buildings with small side setbacks, unlike those of Montreal which are typically attached.

    Going denser though, it seems you get a lot of L shapes, and T shapes for apartment buildings, but also H shapes and fully enclosed courtyards. You'll see these to an extent in the densest older American neighbourhoods, and some newer ones like in LA, but especially in Europe, like in Paris, Budapest or Madrid. These can be large courtyards shared by an entire block of buildings,14.4444059,276m/data=!3m1!1e3
    Or small airshafts enclosed by a single narrow building, which can sometimes be covered (sky light), like at this hotel I stayed at in Prague.!prettyPhoto[gallery01]/1/

    1. For the denser buildings, I know some have argued that courtyard buildings are more efficient for lighting than point buildings/towers. I'm not sure if those arguments took into account the need for streets though.

    2. Another reason may be the lack of regulation regarding shared walls. Shared walls' ownership is confusing, so you need good regulation to clear the air, but even then, some people may prefer not bothering with it. Even a small gap simplifies property issues tremendously.

      I have already touched on what I call the "Traditional European Urban Bloc" (maybe I should shorten it to just Euro-bloc), but I hope to write an article only about them soon (with a mention of some adaptations of it in North America and that one neighborhood in Japan).

      The last article you posted is actually a perfect example of what annoys me with French urbanists. The guy outright says that building higher doesn't increase density, because then you just build things spread out. Which is BS but is a myth commonly parroted by the French, as if Paris was as dense as can be (Barcelona and Hong Kong would disagree)

    3. Yeah, Paris could be denser. It's true that you get diminishing returns with height because trying to have a 0.7 floor plate:lot area ratio with 50 storey buildings is going to be pretty dystopian but I think you could achieve at least 2 times the built density of Paris with high-rises. And you could do that while still having mid rises in between, either as podiums or separate buildings filling a similar role.

  3. It appears to be a legistlation that state that buildings have to be separated form each other 20cm, more or less.
    This way, on case of an earthquake buildings can move independently avoiding damage.

    I still have to find a reliable reference for this.