You will notice how the house on the left has it’s gutters full of ice and icicles are overhanging the gutter and it is apparent that there is an Ice Dam happening.  On this house you can see how the snow is melted away from about 2/3rds of the roof also.  This is a sign that they have too much heat getting into the attic space from poor insulation and poor attic ventilation.  Even if you had some heat loss into your attic space, the roof ventilation can help to force that hot air out via, a good roof intake and exhaust system. ​