Of all the construction-related topics that young builders need to master, one of the most confusing is flashing. If you don’t yet have much job-site experience, you’ve probably got loads of questions: Where do I need to install flashing? What materials should I use? How do I know if a particular product is appropriate or durable enough for a certain application?
It takes many years to understand proper flashing techniques. I have never come across a comprehensive guide to flashing; that book has not yet been written. (That said, my 2003 edition of Architectural Graphic Standards for Residential Construction has an excellent chapter on flashing.)
In light of the fact that flashing manufacturers come out with new products every year, most students of flashing practices will have to make do with a variety of cobbled-together resources, articles, and videos to master this subject.
Flashing has changed in recent decades
We install flashing to prevent rain from entering a building through cracks. Most of the cracks that require flashing are found where dissimilar materials meet — for example, where a chimney meets roofing, where roofing meets a wall, or where siding meets a window — or at the exposed perimeter of surfaces like roofs and walls.
Originally, flashing was made of sheet metal. When I got my first job as a roofer in 1974, peel-and-stick products did not yet exist — or if they existed, they were still unknown on most job sites.
The roofing company I worked for used four kinds of flashing: galvanized steel for drip-edge flashing, aluminum for step flashing on asphalt shingle roofs, copper for most purposes on slate roofs, and lead for chimney counterflashing.
Many (but not all) types of metal flashing include a bend in the sheet metal to direct water in a certain direction — generally, away…