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?

Very common to keep the paper down. They can tell a lot about the condition of the wood when walking on it. If its spongy under their feet then they change it as it will not hold nails.

Besides they make money on new plywood and if they had any feeling that the wood should be replaced they would do it.

Be sure to provide proper ventilation with the new roof. Now is the time to do this. Do not worry about the layers of paper.

They should also be using ice and water dam material along the edges and any valleys to assure against leaks.

quote:

Is this a normal practice?

absolutely yes

Yes, this is a normal practice? Or, yes, they should take up the old tar paper?

Not removing the ashphalt paper is common. There are simply way to many nails and staples left behind to begin to pick off the old paper.
It does no harm leaving it behind.