HI, and thanks to all who take the time to answer this question. I live in the desert southwest(phoenix) and just purchased a home. Recently I noticed a section of my sheathing has warped. It is a small area, between two rafters. I have never seen anything like this before. My question is this, is it possible to replace the small section by cutting out the warped sheathing and replacing it? Would I have to remove a whole layer of shingles across my roof in order to lay a single sheet of underlayment down? Is there a way to apply just a small piece of underlayment down so as to not have any leaks? If so how would I seal it to the adjacent underlayment? The warped part is one foot from the bottom of my roof, over the eve, and the distance of a rafter length(is between the second and third rafter from edge) from the edge of my roof. I would appreciate any ideas of suggestions you may have, as I am planning on repairing it myself and am a newbie at roofing. Thanks again for any help.