Black roof stains

[Jimbo]

I don't know the actual how-to, but my father lives in Yarmouth and had his roof replaced last year. The contractor looked at a house nearby and pointed out the black stains. He said it can be taken care of by putting strips of zinc along the top of the roof. I don't know if it's true, just something I heard. My brother works out on Long I sland and he said they do it there, too.