Any metal roofing experts?

When we get around to finishing our house I am going to have the metal roof removed again....the felt torn up and replaced with the rubberized Ice Dam roofing membrane. Our building has a sealed, non vented style roof. Unless a spray foam insulation, high dollar in this area, is done it is going to be impossible to stop all the heat form escaping. In the heating months we have a bit of water traveling between the felt and the metal. Can't help but wonder how bad it will be if we get several feet of snow again. The Ice Dam membrane is a rubber underlayment. Have talked to my buddy that is going to re-roof the house for us and he told me that he went a full winter with just the Ice Dam membrane on his roof, no metal on top of it. He had zero problems with it. And he lives in the snow belt 25 miles north of us so....