I was at the hardware store this morning and I noticed this ice damming on the roof line. This occurs when the heat from inside meets with the cold on the outside and voila, ice forms. Over time this ice builds up and the weight of the ice itself stresses the structure. During the spring melt this ice simply melts into the walls and creates all sorts of additional damage let alone from the weight. I see this forming on plenty of houses and it can easily be fixed with proper insulation and sealing. This is another great reason to buy a house in the winter.