Slate Roof Central, which gives a great tutorial on identifying and caring for slate.
One of the more common of the PA black slates is "Bangor" slate from Bangor, PA. It is a smooth surfaced finely grained slate that lasts about 90 years. - from Slate Roof CentralSo every year or two we'd get some maintenance repairs done. The problem is, 173 is a tall house with a steep-pitched roof and I gotta tell ya - I ain't goin' up there!
And my neighbor's house:
After removing all the old Pennsylvania Bangor Slate, they put down a new roof deck...
Then of course...the underlayment (felt paper):
Then they did all their stuff and in two days time, a new roof!