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Read an article a couple of days ago pertaining to life spans of roofs. trying to find it again with no luck yet.

 It said that the life span is 19.5 years in the northern states basically because of the snow cover in the winter. Southern states life span was , I think 16 years , simply because they bake in the sun year round.

 I have seen many roofs being replaced in 12-15 years.

 As far as 30-40-or50 year shingles, marketing tactics. They prorate them so bad you will not get piddly  if your roof fails in as short as 10 years !!

 Neighbor had to reroof his house 3 years ago. The shingles were 8 years old.
 The shingle manufacturer admitted they had a bad batch of shingles, but they only gave him $900 . He had to fork out $3200 out of his own pocket !

 Roof size 1800 sq.ft. , if I remember right. 

 He actually recieved a letter from his insurance company stating he had so much time to have the roof fixed or they would cancel his policy !