The upturned leg of the step flashing is behind the vertical drainage plane or sealed to it with adhesive membrane and sheathing tape. Step flashings are interwoven with the shingles and act essentially as shingles with an upturned leg to allow a transition of the vertical drainage plane of the wall to the drainage plane of the roof. Stepped flashing is used where a sloped shingled roof intersects a vertical wall. Flashings are about reducing moisture loading on the building enclosure.
![flash a roof to a vertical wall flash a roof to a vertical wall](https://i.pinimg.com/originals/04/57/40/0457406263614b9d8328becaedf5f13f.jpg)
Flashings must not direct water onto another building element in a way that concentrates moisture loading. To shed water over protruding building elements (such as window/door/trim flashing), orįlashings are needed wherever a drainage plane is terminated as at a roof edge or bottom of wall, or interrupted as at openings, intersection of assemblies, control joints, or penetrations of the drainage plane. To protect an interface between two different enclosure elements (such as roof to wall step flashing), or To direct water that has penetrated behind the cladding back out to the exterior (such as wall base flashing), or Metal flashings on buildings serve a multiple of similar yet slightly different functions. Flashings are integrated with drainage planes creating, for all practical purposes, a flashing for the entire assembly. Flashings are the most under-rated building enclosure component and arguably the most important. The most elegant expression of this concept is a flashing (see Roof to Wall Flashing with Foam Sheathing). Sooner, may not always be practical-such as at window openings where draining a window into a drainage space behind a cladding is often more practical than draining them to the exterior face of the cladding. In general, the sooner water is directed out the better. The “down” direction harnesses the force of gravity and the “out” direction gets the water away from the building enclosure assemblies, openings, components and materials.
![flash a roof to a vertical wall flash a roof to a vertical wall](https://lib.store.yahoo.net/lib/vintagewoodworks/ei-install-shignles-1-1.gif)
Gravity is the driving force behind drainage.