Flashing is used primarily in three areas:
- Roof flashing is placed around discontinuities or objects which protrude from the roof of a building (such as pipes and chimneys or the edges of other roofs) to deflect water away from seams or joints and in valleys where the runoff is concentrated.
- Wall flashing may be embedded in a wall to direct water that has penetrated the wall back outside, or it may be applied in a manner intended to prevent the entry of water into the wall. Wall flashing is typically found at interruptions in the wall, such as windows and points of structural support.
- Sill flashing is a concealed flashing placed under windows or door thresholds to prevent water from entering a wall at those points.
- Roof Penetration Flashings are used to waterproof pipes, supports, cables, and all roof protrusions. Stainless steel penetration flashings have proven to be the longest lasting and most reliable roof flashing type.
A structure incorporating flashing has to be carefully engineered and constructed so that water is directed away from the structure and not inside. Flashing improperly installed can direct water into a building.