Ice back up..... a nasty problem

 Ice dams will form on a roof when snow melts, and then re-freezes at the roof edges. The cause of ice   dams is due to attic temperature being warmer than outside temperature. The attic should be as cold as it is outside. Therefore, proper insulation is vital, as well as proper ventilation in the roof, which is partly  (50%)  from the soffit, and partially (50%) from the roof vents. It is extremely important to make sure that the soffit area inside the attic are not plugged with insulation, in order to allow the cold air to enter the attic. It is also crucial to make sure that holes for fans, light fixtures etc. are properly sealed to stop heat from flowing up to the attic.  The warm air will continue to escape into the attic, and cause the snow to melt, and then re-freeze, causing ice to form. Eventually, when there is enough ice on the roof, the tar lines on the shingles will let go, and when additional melting occurs, the water will come into the house. In the warm weather, those tar lines will re-seal, so water does not come in when it rains, but it is crucial that the attic issues be fixed in order not to have problems the next winter. The Ontario Building codes stipulates that there be a minimum of 2 inches of air space in the attic.