Ice and water barrier is a self adhering rubberized membrane that protects your roof from leaking due to excessive water conditions. These conditions occur during wind driven rain and even more so during water back from ice dams. There are several areas of your roof especially susceptible to the water penetration that ice and water barrier will serve to prevent. The entire perimeter of your roof near the eaves is the most obvious during the winter when you can sometimes see the ice dams from the ground. Other areas you may not think about skylights, chimneys, and all the “channels” where roof lines merge.