[porsche930dude]

im not sure if you can use ice & water over the old shingles. Are your tearing it off or going over. if its only one layer youd be fine going over. We dont go over anything 2 or more layers thick. Tearing off is usually the hardest part of doing a roof so if you can avoid that your much better off. And if you get the same size and style shingles you can do what we call "butt and run" very little measuring or thinking at all because you just nest all the new shingles up to the old ones and that is by far the easyest. Obviously you cant do that if youve got ice and water on there