The last two years I have had water come in due to ice damming under the roof vent from the bathroom exhaust fan. I looked all over the internet and can't seem to find anything on how to prevent this. Huge lump of Ice builds up under the exhaust and any warm days snow will start to melt and find it's way into the bathroom. If I clean the snow out around the ice chunk water immediately stops coming in. Southern Ontario Home attic has blown in insulation (recommended amount for area) R50 I think, no other trouble anywhere else, Shingles are also in worse condition under this exhaust then the rest of the roof How would one go about fixing this, and why don't other people seem to have damming problems at their exhaust, what would different about mine?