The two most common replacements for CCA - alkaline copper quaternary (ACQ) and copper azole (CA) - contain two or three times as much copper, in a chemically more active form. And some studies have shown aluminum to corrode too quickly near the coast, even with the less corrosive CCA preservatives of the past. Aluminum has been the go- to flashing for decades, but contact with ACQ and CA preservatives corrodes the metal. But when lumber treated with chromated copper arsenate (CCA) was phased out for most residential applications in 2.įigure 1). It’s inexpensive, widely available, and fairly easy to work with. Why Not Aluminum? Aluminum has long been the flashing of choice for many builders. Plus, it needs to be accepted by the local building official, so the best advice is to check with him or her before making any final decisions on what type of flashing to use. The ideal flashing should not only resist corrosion, but also hold up in sunlight, install easily, and cost a reasonable amount. Though the International Residential Code specifies that “corrosion resistant” materials be used where porches, decks, or stairs are attached to a wall or floor assembly in wood- frame construction, it doesn’t specify what constitutes a corrosion- resistant material. The question is what kind of flashing works best.
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