Our roof was replaced less than ten years ago and two years ago the bottom half of the shingles on the south side of the roof started falling off. Is there a way to repair the roof or should we just have it redone? We sent a shingle to CertainTeed and they said it wasn't theirs. If we have it redone do we use the asphalt shingles again? If not, what and then we have to do the whole roof if we use something else.