Flashing and caulking in damp areas.

Flashing is designed to keep moisture from penetrating wood and other porous materials. Counter-flashing is used to protect against wind blown rain. Books on Slate roofing installation guides give you a great deal of information on protecting your roof and wet areas around the home. When  Caulk needs used oil based urethane which will outlast water base every-time.Remember water runs downhill but driving wind can force water uphill . Membranes under you shingles can save you a lot of money and grief if some shingles blow off  your home during a storm.Don't forget to use lead boots on roof penetrations they can last 10x longer than  plastic ones.