Another option is to make a series of holes in the wall under the cornice or a lot of dormers on the roof. I saw an inexpensive option, and when many existing ventilation pipes cut into the existing roof, I do not know about the efficiency. But yes, you cannot stop existing dormer windows, as it often happens.
Here, for example, on this roof icicles, this winter did not see, and this is a rare exception. Here there is a continuous ventszazor under the cornice, for some reason the cornice was not sewn at all, and on the reverse side in this attic, there are open holes directly in the wall, that is, the air freely walks in the attic. Pay attention that on this roof the snow lies, on the right in the frame the snow on the roof melted.
Still need to be told that the melting snow on the roofs leads not only to the formation of life-threatening icicles but also:
To the winter leaks of the roof, when the water, resting on the ice dam, rises to the level of roof joints and then flows to someone in the apartment and spoils repairs or soaks the wall and leads to a subsequent collapse of the plaster to icing of sidewalks under the pipes and in general along the buildings
Some wealthy homeowners solve the problem of icicles by electrically heating the cornice with a cable. In this case, the question passes under the feet of pedestrians. Slipping, of course, is not as scary as getting under the icicle, but it still cannot be called a full-fledged solution.