Heating line on roof

[swimmer_spe]

Last year, I had an ice dam about 6''-12'' thick. The problem was lack of insulation in an area around the place where the ice dam occurred. That has since been fixed.
I have a low sloped mansard roof. Should I put up a heat line to prevent an ice dam, or should I be good?

 

[nealtw]

Do you have venting to take the heat away from the top of the wall. I think you might want the heat just for insurance.