Q: A friend recently mentioned in passing he thought some of the "flashing" on my roof looked as if it were in rough shape. Can you explain exactly what roof flashing is?
—Britney, Fort Worth, Texas
A: Tom Silva replies: Flashing is just material—usually aluminum or galvanized steel—that's used over joints in roof and wall construction to prevent water seeping in and causing damage. Depending on the style of your house's roof, you probably have it in the valleys, around the chimney and pipes, and around any dormer windows or skylights. Most damage shows up either in flashing that's deteriorating due to weathering and oxidizing, or in flashing that has come loose.
I can't say for sure without seeing your roof, but most flashing problems can be patched or repaired fairly easily. Professional roofers typically cut and shape their own flashing from sheet metal, but the most common flashing pieces also come pre-formed and can be applied without much difficulty using caulking or roof cement.
A word of warning: Because of the danger involved, I never recommend people do work on roofs unless they are professionals or they're used to being on roofs and are familiar with the one they're working on. So if your flashing needs any significant repairs, consider hiring a contractor to do it for you.