They are more properly called cornice returns i think but i d rather call them eave returns.
Roof cornice return.
A cornice return is a triangular piece of material that is placed below the rake fascia on the corner of a roof.
It is a short horizontal extension of the cornice that occurs on each side of the gable end of the building see picture of the härnösands rådhus with two of these.
Eave returns are the decorative extension of the roof eave that wraps around the gable end of the house.
A cornice return is an architectural detail that occurs where the horizontal cornice of a roof connects to the rake of a gable.
Most greek revival buildings have substantial cornices that extended into gable ends as returns below picture.
But there are ways to ensure they are sound.
The greek revival roof return s tyle emulated the temple forms of ancient greece resulting in the creation of straightforward box like buildings we see in historic towns of america.
Heres some terminology for you click to enlarge.
Done properly this is hip cut back to the wall and the eavestrough runs all the way around back to the wall.
If the overhang is 24 then it normally get s returned double that at the gable.
Also called an eave return a cornice return is a graceful way to transition the eave and the main fascia board around the gable end of a house.
This article has some good snobbish info about how cornice returns are supposed to look.
Sometimes this helps with drainage and other times the cornice return is more of a decorative piece.