My roof isn't very old (about4years) The roof was done by a "roofer" shortly after it was finished I had a nasty leak upon inspection I discovered no felt!(I asked for complete tear off and new felt durring the bid)I fixed that and had no problems untill Hurricane Rita. To my surprise I was not missing a single shingle and it looked to have only had minor leaks. Now I have random leaks durring long storms (as in days/weeks) I am sure alot of this has to do with the 1 1/2 inch to 12 inch pitch. I was going to do a tearoff myself and go with new 30pound felt and 3tab shingles. Lattly I have been thinking about leaving the roof and just putting another layer on,this would be alot faster and seems like it would be more protection. I was told that areas that have alot of snow that a double layer roof is common because the snow doesn't drain. That seems like the problem I have(can't drain fast enough).