This picture of an English village shows a row of houses that appear to share walls. Is there a reason why they were built this way? 20th century condos in the US share walls, but this is primarily because they are built by a single developer and it’s more cost effective. The houses in the photograph linked above appear to have different architectural styles, so it’s unclear that they were built by a single developer. Why share walls then?
On a slight tangent, those houses look more like from the 16th century than from the 18th century to me. However, I suspect that doesn’t affect the answer.
You’re probably right, on both counts.
I think the OP answered his own question. It’s cheaper and faster to build houses that share a wall.
I’m wondering why they curved that building in the photo? That seems pretty difficult to get a smooth curve.
It’s also a much more efficient use of limited land. Same reason they built them just that way in Boston and many other US cities, most notably New York.
Because the Earth is curved, duh 
I can see that cost-savings might be a reason. But if I’ve already built a house, my future neighbor may have a tough time convincing me to piggy off my already-built wall.
Exterior walls require windows and brick or stucco finishes. Insulation is used in modern homes.
The people in the interior section of homes only have 2 exterior walls (front,back). That should keep the home warmer. A big factor before modern central heating.
The curved appearance is a result of combining several photos into a panorama. The row of houses is on the south side of the High Street in Lacock, Wiltshire, which you can see is pretty straight in Google Maps
What makes you think they weren’t all built by the same developer, albeit not all at the same time?
Prior to the 20th century, most houses in Britain were owned by the landlord, and in a smallish village, most houses would be owned by the same landlord (“developer”).
The Brits other popular style is the semi-detached.
We have duplexes in the US. Usually they are fairly low rent places. Sometimes large houses that were divided to generate extra income.
The Brits build very large and expensive semi-detached. They seem to like sharing a wall.
I forgot about those. Those types of buildings are rare out here in the west coast.
There are multiple reasons (most of them economical) for building semi-detached, but I think the main one is that land here is expensive.
[ul]
[li]If you want to build houses that have a driveway or at least local pedestrian access to the rear, they need a gap to the side - a gap to the other side would cost more (and would either be useless if narrow, or redundant if broad.[/li][li]Also, services (water, sewage) can be connected from street to two houses via a shared trench and pipework (shared between houses, not shared between water and sewage, I mean).[/li][li]And there’s a slight saving in terms of building and roofing materials[/li][/ul]
(not all of these might apply to all examples)
Most people would prefer to live in a detached house, but semi-detached houses are significantly cheaper to buy.
The houses linked in the OP may not have originally been owned by the people who lived in them - they may well have been built by the landowner and rented out (and thus, the question of accepting a new house built on the side of your own may have been moot) - with additional residences being added on the end to increase the accommodation capacity.
It sounds like this was the case for this location (Lacock) - the village was part of an estate, owned at one point by one of the pioneers of photography. Lacock - Wikipedia
ETA: notice the doors and window frames are all painted the same colour - this often indicates that the houses are still part of an estate and are rented, not owned by their residents.
True in some cases no doubt, but we also build the smallest new houses in Western Europe.
There isn’t a lot of land over here. A detached house (no shared walls) is generally speaking very expensive. In my neighbourhood, I’d guess the cheapest detached house would cost about $600,000-800,000 and you’d mainly be paying for the fact it was detached than the house being particularly impressive
Not in San Francisco, they’re not. We have 25-ft wide lots and 25-ft wide houses. Here’s a sample in my neighborhood.
Land is very expensive here. However. note that the walls are not shared. Each house has separate walls, but the side walls butt up against each other. It saves re-painting them all the time. Actually it makes it impossible to re-paint them, ever. I seem to recall, on one of the rare occasions I was on my roof, that there is something across the “gap” between the walls to prevent rain going down and giving dry rot a chance to get started.
They are called terraced houses and the Brits built them like that to save space.
https://lh4.googleusercontent.com/fLbOojJERynBDCykdhZ1_mmU149IWyGLQxbo6eSiE2lt=w539-h363-p-no
What others have said. They take up less space, and they’re cheaper to construct and to heat, once constructed.
In a typical English village, few of the residents owned their own houses; they rented them from landlords who typically owned, and had developed, much of the village. There would be a small number of larger, free-standing houses for, e.g., the vicar, but most of the residents were labourers, craftsmen or traders on a small scale, and low or low-ish cost housing was the priority.
Do a Google Image search for San Francisco Row Houses to see some actual pictures.
Here’s one of some ornately painted houses in Haight Ashbury, from the Wiki page Painted Ladies.
A very substantial portion of San Francisco consists of row houses. Many are like Roderick Femm describes: Each house actually has its own walls on all sides, but they are hard up against the neighboring houses’ walls. In other places, the houses are very close together, with only a few inches separating them, as the houses in this picture appear to be.
The prospect of such houses catching on fire must be a perpetual nightmare for all who live in those neighborhoods. If one house goes up, the entire block might go up.
I think most people in Britain will have lived in a terraced house at some point in their lives. I’ve lived in several - my current house is a late 19th century terrace (looks like this). The Victorians built loads and loads of them and many still populate urban centres.
We’re a very over-populated island. Land is very expensive, and there are strict laws in many parts against building on ‘green belt’, ie land which has never been built on previously, such as farm land.