Window Flashing

Window flashing is a thin continuous piece of material that is installed to prevent water from getting into a structure from an angle or joint near windows. It is key to preventing water intrusion. Window flashing is arranged in a manner that directs water down and away from the structure. It is typically used on roofs, around windows and doors, and around any opening for pipes or electrical lines. Window flashing can be exposed or concealed. Exposed flashing—as seen on roofs—can be copper, lead-coated copper, aluminum, galvanized steel, galvanized sheet metal, stainless steel, mineral-surfaced roll roof flashing, or ice and water barrier membrane.


The flashing that is concealed within a construction assembly can be sheet metal (as aluminum flashing around in corners) or a water proofing membrane such as bituminous fabric or plastic sheet material (typically used around windows and doors).

Flashing can be used in a number of ways: Roof flashing is used on roof hips or installed around objects that 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. Wall flashing is embedded in a wall to either direct water that has penetrated the wall back outside or installed to prevent the entry of water into the wall. Wall flashing is typically found around windows and doors. Sill window flashing is a concealed flashing that is installed under windowsills or door thresholds to prevent water from entering a wall at those points. Base flashing is found at the base of a wall and usually has weep holes to let water escape. It is installed at the building grade.

Window flashing is important because it is the only way to prevent water intrusion. Improperly flashed roofs, windows, doors, and other openings will leak. A good seal guides water around the opening and keeps the interior wall protected and dry. Properly installed, window flashing will control almost all water intrusion into the structure and will work for the life of the structure.

For more information about window flashing and other trim materials, please visit CertainTeed’s trim products page.

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