It is an effect of closed perimeter block development.
The address 'Arendalsgata No 3: Sagene working class society' looks like this from above:
Orientation is the same as in the photo in question, so the building we want is in the lower right. The buildings to the left of that 'empty' edge with the small shed/garage are of a very different and later, post-...
In the USA, in the city of Philadelphia, Pennsylvania, there are vast regions containing what are called "row houses", houses built touching their neighbors on either side, extending for many square miles. I lived for most of my childhood in a "duplex" house, which had a side yard on one side connecting the front and back yards, and on ...
Because in many cases, as here (see below), the complex is built to within an inch or two of the property line. Why you ask? A few reasons:
Zoning allows it.
Property value is a sum of the value of three things:
a. the building;
b. the lot green space; and
c. the lot built-up space.
When value of the building is, or is expected soon to be, much greater ...