Lean-to

A lean-to is a type of simple structure originally added to an existing building with the rafters "leaning" against another wall.

Free-standing structures open on one or more sides (colloquially referred to as lean-tos in spite of being unattached to anything) are generally used as shelters.

Sometimes, it covers an external staircase, as in a 15th century addition against one of the walls of the large chapter room of the cathedral of Meaux.

[1] A lean-to is originally defined as a structure in which the rafters lean against another building or wall, also referred to in prior times as a penthouse.

This style of lean-to is popular in Finland and Scandinavia, and known as a laavu in Finnish, gapskjul or slogbod in Swedish, and gapahuk in Norwegian.