While inspecting the roof of a 14 year old house, I discovered two layers of shingles along the outside edges of the roof. There was only one flashing and the bottom layer of shingles appeared to be the same, color and texture as the top layer. Viewing from the attic hatch did not show double rows of nails. Do roofers sometimes add a layer of shingles arount the outside edge of the roof for extra protection?