Aluminum flashing is composed of continuous pieces of metal that prevent water from passing through a joint or angle into the interior of a structure. The idea behind flashing is that having an additional barrier put over an area where moisture can penetrate will make it nearly impossible for water to enter because the water must work against gravity. Aluminum and other metal flashings are used on surfaces exposed to weather.
Types of Flashing
Exposed flashing is composed of thin sheet metal. Aluminum is one of the metals most commonly used for flashing. Other metals used for this purpose include copper, galvanized steel, stainless steel, zinc alloy, lead and lead-coated copper. Concealed flashing may also be made of aluminum and other metals, but may also be made of bituminous fabric or plastic sheeting.
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Aluminum flashing is an essential part of a roofing structure because of the numerous valleys and joints involved in its construction. Flashing is essential in roof valleys as water accumulates in low spots through normal runoff as well as through ice dams in winter. Flashing is also placed near eaves and on roofs around objects such as pipes and chimneys that protrude from the surface and form significant angles where water can intrude.
Often manufactured in metal roll form, aluminum flashing can be used in a variety of other construction applications. Angle or wall flashing may be embedded in a wall to prevent moisture seepage, typically around windows and at similar points of structural support. Sill flashing or drip caps, are concealed, and put under windows or door thresholds. Base flashing is found at the bottom of walls and are normally set at a building grade. Foundation straps are found near basements, while sheet flashing can be used in a variety of applications such as decks and sidewalls.
Advantages and Disadvantages
One advantage of aluminum flashing is that its cost is midrange of the varieties of sheet metal flashing. It's soft and workable, holding its shape well and is also easily installed, although it is not as strong as galvanized flashing. Aluminum must be coated to have direct contact with cement-based materials including fiber-cement siding and trim, because of the cement's corrosive nature, which adds to cost. Joints should be lapped, mechanically fastened and caulked to create watertight seams. Aluminum flashing is manufactured in rolls, sheets and pre-formed shapes for chimneys, vents and other specific applications. Some manufacturers offer aluminum flashing in a variety of colors to match exterior paint and trim.