The All Saints, Chevy Chase, church was built in 1901 with Virginia Buckingham slate. They put on additions in the 1940's and 1950's with Pennsylvania Black slate, and then another addition in the 1990's with Spanish Black slate.
Unfortunately, Pennsylvania Black slate doesn't wear as well as Virginia Buckingham and that material difference was becoming obvious; the newer roofs were leaking and shedding slates. Since the original roofs - almost a century old - were still in excellent condition, the additions would be repaired with Virginia Buckingham.
To this end, we removed all of the Pennsylvania Black slate from the additions and replaced them with Virginia Buckingham. We also replaced all the copper flashings and gutters with 20 ounce copper.