I'm having a new roof put on due to hurricane Ike. I noticed the crew that was sent over is simply taking off the old shingles and then laying new tarp paper over the old tarp paper before putting on the new shingles. Is this a normal practice? They did in fact replace one peice of plywood so far on the back of the house. when I asked how they knew to replace it, they said they could feel the sag with their feet. Shouldn't they also take up all the old tar paper to know if there is damage underneath?