Water is both the most useful and the most damaging liquid. It needs to be moved off of or out of our buildings almost religiously. These details cover the most common flashings for homes, especially the weatherlap — shingle-style shedding of water from one overlapping component to the next. There are very few sealants or caulks in these details (especially compared to the air-sealing details). When caulks or sealants are exposed to liquid water and the sun, they will eventually fail. And when they do, they can trap as much water as they were intended to keep out. There is seldom just one way to flash any one penetration, and never just one flashing material; these details often represent just one of many best practice approaches.