My vent stack is gettting iced up. The stack happens to be directly over the shower. Can I jun hot water in the shower to help melt the vent ice or will this just add to the problem. I do have access to the pipe where it goes through the roof, it is a heated area. Thought maybe warming the pipe in the attic but not sure if that would hurt or help. I don't feel comfortable in attempting to get on the roof metal snow roof with high pitch and lots of snow and ice around.

What kind of pipe?

Sorry I forgot to mention it is 3 in pvc

I am assuming the icing occurs from the warm, moist sewer gases rising creating condensation, which freezes before it can run down the pipe to the warmer area. Running hot water down the drain will not help, may create more condensation, therefore more icing.
Heating the pipe just below where it passes through the roof line should melt the ice but will probably take some time. I would use a hair dryer for that. You could use a heat gun if you are careful not to heat the pipe too much in one area.

Does this occur very often?

I noticed some icing efore but not as severe as this time as our temps at night have been below zero for a couple of weeks now. Certainly I would like to put in a fix that I can use permanently for situations that might develop in the future.

It doesn't get that cold for that long where I live. If it did I think I would move. In the mean time you might want to look around and see what your neighbors may have done. If you don't find any better solutions, you may want to consider the following (in the spring time of course).