and henry navarro who is the roofing supervisor for the port of san francisco. for 20 years? >> 23 years. >> you have seen roofs come and roofs go. >> 38 years worth. >> how long does a roof usually last? >> dependos the climate and the pitch of the roof. >> uh-huh. from? >> a couple of years. >> from 15. i asbestos roofs go for 15 years. you said you put a roof on your house you expect to last? >> 75 year. i wish you luck. >> only going to do it once. >> people know what they are doing with their roofs that will last for a long time and not have to redo it. is this the same concept as painting where it takes a lot of effort to get ready and the prep work and the materials are such a large part of the expense or the materials are a big piece of the expense. i tell people in painting, buy the best material you can because you don't want to keep redog it. is this the same concept. >> it is the prep work is important if you go over a bad part tell effect the roof. >> going over a bad surface. the implication is most buildings in san francisco are existing buildings. we don't hav