What is a Flashing in Construction?

January 26, 2024

Many elements in construction go unnoticed, but without flashing, buildings would suffer from far more leaks and water damage. Flashing is thin sheets of impervious material that prevent moisture from passing through joints and crevices. It is used around chimneys, vent pipes, skylights, windows and doors and other locations in the walls or roofs of a structure. It decreases water penetration to make buildings more durable and reduce indoor mold problems. It can be fabricated from a variety of materials, but copper, galvanized steel, lead or aluminum are most commonly used in exposed/exterior flashing conditions.

Frequently used areas of flashing include roof valleys and ridges, where a lower height roof meets the wall or a masonry parapet wall, at gutter stops, and where a wall or chimney intersects the roof. Chimney flashing includes counter or cap flashing and a cricket or back flashing (see photo). When multiple strips of flashing are employed together the term 'counter-flashing' is commonly used, as is 'cap-flashing' when the pieces overlap each other.

Flashings are fabricated with a large clamp like tool called a brake that is fed an aluminum sheet from a rolled coil. It is bent into various shapes to fit the abutting surfaces. It is also welded where necessary to strengthen the connection. In shingle roofing, it is often weaved in between the shingles. In some cases, it is crimped with a vee shaped 'flashing cleat' to add additional strength to the connection.


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